Articles de revues : « Cardiac kinematics »

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Cutrì, Elena, Paola Bagnoli, Emanuela Marcelli, Federico Biondi, Laura Cercenelli, Maria Laura Costantino, Gianni Plicchi et Roberto Fumero. « A Mechanical Simulator of Cardiac Wall Kinematics ». ASAIO Journal 56, n^o 3 (mai 2010) : 164–71. http://dx.doi.org/10.1097/mat.0b013e3181d7db0c.

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Tsamis, Alkiviadis, Allen Cheng, Tom C. Nguyen, Frank Langer, D. Craig Miller et Ellen Kuhl. « Kinematics of cardiac growth : In vivo characterization of growth tensors and strains ». Journal of the Mechanical Behavior of Biomedical Materials 8 (avril 2012) : 165–77. http://dx.doi.org/10.1016/j.jmbbm.2011.12.006.

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Damen, Frederick W., David T. Newton, Guang Lin et Craig J. Goergen. « Machine Learning Driven Contouring of High-Frequency Four-Dimensional Cardiac Ultrasound Data ». Applied Sciences 11, n^o 4 (13 février 2021) : 1690. http://dx.doi.org/10.3390/app11041690.

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Automatic boundary detection of 4D ultrasound (4DUS) cardiac data is a promising yet challenging application at the intersection of machine learning and medicine. Using recently developed murine 4DUS cardiac imaging data, we demonstrate here a set of three machine learning models that predict left ventricular wall kinematics along both the endo- and epi-cardial boundaries. Each model is fundamentally built on three key features: (1) the projection of raw US data to a lower dimensional subspace, (2) a smoothing spline basis across time, and (3) a strategic parameterization of the left ventricular boundaries. Model 1 is constructed such that boundary predictions are based on individual short-axis images, regardless of their relative position in the ventricle. Model 2 simultaneously incorporates parallel short-axis image data into their predictions. Model 3 builds on the multi-slice approach of model 2, but assists predictions with a single ground-truth position at end-diastole. To assess the performance of each model, Monte Carlo cross validation was used to assess the performance of each model on unseen data. For predicting the radial distance of the endocardium, models 1, 2, and 3 yielded average R2 values of 0.41, 0.49, and 0.71, respectively. Monte Carlo simulations of the endocardial wall showed significantly closer predictions when using model 2 versus model 1 at a rate of 48.67%, and using model 3 versus model 2 at a rate of 83.50%. These finding suggest that a machine learning approach where multi-slice data are simultaneously used as input and predictions are aided by a single user input yields the most robust performance. Subsequently, we explore the how metrics of cardiac kinematics compare between ground-truth contours and predicted boundaries. We observed negligible deviations from ground-truth when using predicted boundaries alone, except in the case of early diastolic strain rate, providing confidence for the use of such machine learning models for rapid and reliable assessments of murine cardiac function. To our knowledge, this is the first application of machine learning to murine left ventricular 4DUS data. Future work will be needed to strengthen both model performance and applicability to different cardiac disease models.

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Fassina, Lorenzo, Giovanni Magenes, Roberto Gimmelli et Fabio Naro. « Modulation of the Cardiomyocyte Contraction inside a Hydrostatic Pressure Bioreactor:In VitroVerification of the Frank-Starling Law ». BioMed Research International 2015 (2015) : 1–7. http://dx.doi.org/10.1155/2015/542105.

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We have studied beating mouse cardiac syncytiain vitroin order to assess the inotropic, ergotropic, and chronotropic effects of both increasing and decreasing hydrostatic pressures. In particular, we have performed an image processing analysis to evaluate the kinematics and the dynamics of those pressure-loaded beating syncytia starting from the video registration of their contraction movement. By this analysis, we have verified the Frank-Starling law of the heart inin vitrobeating cardiac syncytia and we have obtained their geometrical-functional classification.

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Fassina, Lorenzo, Marisa Cornacchione, Manuela Pellegrini, Maria Evelina Mognaschi, Roberto Gimmelli, Andrea Maria Isidori, Andrea Lenzi, Giovanni Magenes et Fabio Naro. « Model of Murine Ventricular Cardiac Tissue for In Vitro Kinematic-Dynamic Studies of Electromagnetic and β-Adrenergic Stimulation ». Journal of Healthcare Engineering 2017 (2017) : 1–7. http://dx.doi.org/10.1155/2017/4204085.

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In a model of murine ventricular cardiac tissue in vitro, we have studied the inotropic effects of electromagnetic stimulation (frequency, 75 Hz), isoproterenol administration (10 μM), and their combination. In particular, we have performed an image processing analysis to evaluate the kinematics and the dynamics of beating cardiac syncytia starting from the video registration of their contraction movement. We have found that the electromagnetic stimulation is able to counteract the β-adrenergic effect of isoproterenol and to elicit an antihypertrophic response.

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Rozzi, Giacomo, Francesco P. Lo Muzio, Camilla Sandrini, Stefano Rossi, Lorenzo Fassina, Giuseppe Faggian, Michele Miragoli et Giovanni Battista Luciani. « Real-time video kinematic evaluation of the in situ beating right ventricle after pulmonary valve replacement in patients with tetralogy of Fallot : a pilot study ». Interactive CardioVascular and Thoracic Surgery 29, n^o 4 (9 juin 2019) : 625–31. http://dx.doi.org/10.1093/icvts/ivz120.

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Abstract OBJECTIVES The timing for pulmonary valve replacement (PVR) after tetralogy of Fallot repair is controversial, due to limitations in estimating right ventricular dysfunction and recovery. Intraoperative imaging could add prognostic information, but transoesophageal echocardiography is unsuitable for exploring right heart function. Right ventricular function after PVR was investigated in real time using a novel video-based contactless kinematic evaluation technology (Vi.Ki.E.), which calculates cardiac fatigue and energy consumption. METHODS Six consecutive patients undergoing PVR at 13.8 ± 2.6 years (range 6.9–19.8) after the repair of tetralogy of Fallot were enrolled. Mean right ventricular end-diastolic and end-systolic volume at magnetic resonance imaging were 115.6 ± 16.2 ml/m2 and 61.5 ± 14.6 ml/m2, respectively. Vi.Ki.E. uses a fast-resolution camera placed 45 cm above the open chest, recording cardiac kinematics before and after PVR. An algorithm defines cardiac parameters, such as energy, fatigue, maximum contraction velocity and tissue displacement. RESULTS There were no perioperative complications, with patients discharged in satisfactory clinical conditions after 7 ± 2 days (range 5–9). Vi.Ki.E. parameters describing right ventricular dysfunction decreased significantly after surgery: energy consumption by 45% [271 125 ± 9422 (mm/s)2 vs 149 202 ± 11 980 (mm/s)2, P = 0.0001], cardiac fatigue by 12% (292 671 ± 29 369 mm/s2 vs 258 755 ± 42 750 mm/s2, P = 0.01), contraction velocity by 54% (3412 ± 749 mm/s vs 1579 ± 400 mm/s, P = 0.0007) and displacement by 23% (27 ± 4 mm vs 21 ± 4 mm, P = 0.01). Patients undergoing PVR at lower end-diastolic volumes, had greater functional recovery of Vi.Ki.E. parameters. CONCLUSIONS Intraoperative Vi.Ki.E shows immediate recovery of right ventricular mechanics after PVR with less cardiac fatigue and energy consumption, providing novel insights that may have a prognostic relevance for functional recovery.

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Dabiri, John O., et Morteza Gharib. « The role of optimal vortex formation in biological fluid transport ». Proceedings of the Royal Society B : Biological Sciences 272, n^o 1572 (21 juin 2005) : 1557–60. http://dx.doi.org/10.1098/rspb.2005.3109.

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Animal phyla that require macro-scale fluid transport for functioning have repeatedly and often independently converged on the use of jet flows. During flow initiation these jets form fluid vortex rings, which facilitate mass transfer by stationary pumps (e.g. cardiac chambers) and momentum transfer by mobile systems (e.g. jet-propelled swimmers). Previous research has shown that vortex rings generated in the laboratory can be optimized for efficiency or thrust, based on the jet length-to-diameter ratio ( L / D ), with peak performance occurring at 3.5< L / D <4.5. Attempts to determine if biological jets achieve this optimization have been inconclusive, due to the inability to properly account for the diversity of jet kinematics found across animal phyla. We combine laboratory experiments, in situ observations and a framework that reduces the kinematics to a single parameter in order to quantitatively show that individual animal kinematics can be tuned in correlation with optimal vortex ring formation. This new approach identifies simple rules for effective fluid transport, facilitates comparative biological studies of jet flows across animal phyla irrespective of their specific functions and can be extended to unify theories of optimal jet-based and flapping-based vortex ring formation.

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Douglas, A. S., E. K. Rodriguez, W. O'Dell et W. C. Hunter. « Unique strain history during ejection in canine left ventricle ». American Journal of Physiology-Heart and Circulatory Physiology 260, n^o 5 (1 mai 1991) : H1596—H1611. http://dx.doi.org/10.1152/ajpheart.1991.260.5.h1596.

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Understanding the relationship between structure and function in the heart requires a knowledge of the connection between the local behavior of the myocardium (e.g., shortening) and the pumping action of the left ventricle. We asked the question, how do changes in preload and afterload affect the relationship between local myocardial deformation and ventricular volume? To study this, a set of small radiopaque beads was implanted in approximately 1 cm3 of the isolated canine heart left ventricular free wall. Using biplane cineradiography, we tracked the motion of these markers through various cardiac cycles (controlling pre- and afterload) using the relative motion of six markers to quantify the local three dimensional Lagrangian strain. Two different reference states (used to define the strains) were considered. First, we used the configuration of the heart at end diastole for that particular cardiac cycle to define the individual strains (which gave the local “shortening fraction”) and the ejection fraction. Second, we used a single reference state for all cardiac cycles i.e., the end-diastolic state at maximum volume, to define absolute strains (which gave local fractional length) and the volume fraction. The individual strain versus ejection fraction trajectories were dependent on preload and afterload. For any one heart, however, each component of absolute strain was more tightly correlated to volume fraction. Around each linear regression, the individual measurements of absolute strain scattered with standard errors that averaged less than 7% of their range. Thus the canine hearts examined had a preferred kinematic (shape) history during ejection, different from the kinematics of filling and independent or pre-or afterload and of stroke volume.

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Kindberg, K., M. Karlsson, N. B. Ingels et J. C. Criscione. « Nonhomogeneous Strain From Sparse Marker Arrays for Analysis of Transmural Myocardial Mechanics ». Journal of Biomechanical Engineering 129, n^o 4 (24 novembre 2006) : 603–10. http://dx.doi.org/10.1115/1.2746385.

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Background: Knowledge of normal cardiac kinematics is important when attempting to understand the mechanisms that impair the contractile function of the heart during disease. The complex kinematics of the heart can be studied by inserting radiopaque markers in the cardiac wall and study the pumping heart with biplane cineradiography. In order to study the local strain, the bead array was developed where small radiopaque beads are inserted along three columns transmurally in the left ventricle. Method: This paper suggests a straightforward method for strain computation, based on polynomial least-squares fitting and tailored for combined marker and bead array analyses. Results: This polynomial method gives small errors for a realistic bead array on an analytical test case. The method delivers an explicit expression of the Lagrangian strain tensor as a polynomial function of the coordinates of material points in the reference configuration. The method suggested in this paper is validated with analytical strains on a deforming cylinder resembling the heart, compared to a previously suggested finite element method, and applied to in vivo ovine data. The errors in the estimated strain components are shown to remain unchanged on an analytical test case when evaluating the effects of one missing bead. In conclusion, the proposed strain computation method is accurate and robust, with errors smaller or comparable to the current gold standard when applied on an analytical test case.

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Loschak, Paul M., Alperen Degirmenci, Cory M. Tschabrunn, Elad Anter et Robert D. Howe. « Automatically steering cardiac catheters in vivo with respiratory motion compensation ». International Journal of Robotics Research 39, n^o 5 (19 février 2020) : 586–97. http://dx.doi.org/10.1177/0278364920903785.

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A robotic system for automatically navigating ultrasound (US) imaging catheters can provide real-time intra-cardiac imaging for diagnosis and treatment while reducing the need for clinicians to perform manual catheter steering. Clinical deployment of such a system requires accurate navigation despite the presence of disturbances including cyclical physiological motions (e.g., respiration). In this work, we report results from in vivo trials of automatic target tracking using our system, which is the first to navigate cardiac catheters with respiratory motion compensation. The effects of respiratory disturbances on the US catheter are modeled and then applied to four-degree-of-freedom steering kinematics with predictive filtering. This enables the system to accurately steer the US catheter and aim the US imager at a target despite respiratory motion disturbance. In vivo animal respiratory motion compensation results demonstrate automatic US catheter steering to image a target ablation catheter with 1.05 mm and 1.33° mean absolute error. Robotic US catheter steering with motion compensation can improve cardiac catheterization techniques while reducing clinician effort and X-ray exposure.

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Hayabuchi, Yasunobu, Akemi Ono, Yukako Homma et Shoji Kagami. « Assessment of pulmonary arterial compliance evaluated using harmonic oscillator kinematics ». Pulmonary Circulation 7, n^o 3 (16 juin 2017) : 666–73. http://dx.doi.org/10.1177/2045893217714781.

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We hypothesized that KPA, a harmonic oscillator kinematics-derived spring constant parameter of the pulmonary artery pressure (PAP) profile, reflects PA compliance in pediatric patients. In this prospective study of 33 children (age range = 0.5–20 years) with various cardiac diseases, we assessed the novel parameter designated as KPA calculated using the pressure phase plane and the equation KPA = (dP/dt_max)2/([Pmax – Pmin])/2)2, where dP/dt_max is the peak derivative of PAP, and Pmax – Pmin is the difference between the minimum and maximum PAP. PA compliance was also calculated using two conventional methods: systolic PA compliance (sPAC) was expressed as the stroke volume/Pmax – Pmin; and diastolic PA compliance (dPAC) was determined according to a two-element Windkessel model of PA diastolic pressure decay. In addition, data were recorded during abdominal compression to determine the influence of preload on KPA. A significant correlation was observed between KPA and sPAC (r = 0.52, P = 0.0018), but not dPAC. Significant correlations were also seen with the time constant (τ) of diastolic PAP (r = −0.51, P = 0.0026) and the pulmonary vascular resistance index (r = −0.39, P = 0.0242). No significant difference in KPA was seen between before and after abdominal compression. KPA had a higher intraclass correlation coefficient than other compliance and resistance parameters for both intra-observer and inter-observer variability (0.998 and 0.997, respectively). These results suggest that KPA can provide insight into the underlying mechanisms and facilitate the quantification of PA compliance.

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Truong, Quynh A., Wai-ee Thai, Bryan Wai, Qing Zhou, Heather Brown, Richard Bennett, Jonathan Beaudoin, Jagmeet Singh, Conor Barrett et Stephan Danik. « A NEW METHOD USING CARDIAC CT KINEMATICS TO REFLECT THE ACTIVATION PATTERN VISUALIZED WITH ELECTROANATOMICAL MAP : CARDIAC CT PHASE TIME VELOCITY ACTIVATION-ENCODED MAP (ACTIVATE) ». Journal of the American College of Cardiology 61, n^o 10 (mars 2013) : E913. http://dx.doi.org/10.1016/s0735-1097(13)60913-4.

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Fassina, Lorenzo, Antonio Di Grazia, Fabio Naro, Lucia Monaco, Maria Gabriella Cusella De Angelis et Giovanni Magenes. « Video Evaluation of the Kinematics and Dynamics of the Beating Cardiac Syncytium : An Alternative to the Langendorff Method ». International Journal of Artificial Organs 34, n^o 7 (juillet 2011) : 546–58. http://dx.doi.org/10.5301/ijao.2011.8510.

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Yip, Michael C., Jake A. Sganga et David B. Camarillo. « Autonomous Control of Continuum Robot Manipulators for Complex Cardiac Ablation Tasks ». Journal of Medical Robotics Research 02, n^o 01 (26 février 2017) : 1750002. http://dx.doi.org/10.1142/s2424905x17500027.

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Continuum manipulators enable minimally-invasive surgery on the beating heart, but the challenges involved in manually controlling the manipulator’s tip position and contact force with the tissue result in failed procedures and complications. The objective of this work is to achieve autonomous robotic control of a continuum manipulator’s position and force in a beating heart model. We present a model-less hybrid control approach that regulates the tip position/force of manipulators with unknown kinematics/mechanics, under unknown constraints along the manipulator’s body. The algorithms estimate the Jacobian in the presence of heartbeat disturbances and sensor noise in real time, enabling closed-loop control. Using this model-less control approach, a robotic catheter autonomously traced clinically relevant paths on a simulated beating heart environment while regulating contact force. A gating procedure is used to tighten the treatment margins and improve precision. Experimental results demonstrate the capabilities of the robot ([Formula: see text][Formula: see text]mm–[Formula: see text][Formula: see text]mm tracking error) while user demonstrations show the difficulty of manually performing the same task ([Formula: see text][Formula: see text]mm–[Formula: see text][Formula: see text]mm tracking error). This new, robotically-enabled contiguous ablation method could reduce ablation path discontinuities, improve consistency of treatment, and therefore improve clinical outcomes.

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Ghosh, Erina, Leonid Shmuylovich et Sándor J. Kovács. « Vortex formation time-to-left ventricular early rapid filling relation : model-based prediction with echocardiographic validation ». Journal of Applied Physiology 109, n^o 6 (décembre 2010) : 1812–19. http://dx.doi.org/10.1152/japplphysiol.00645.2010.

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During early rapid filling, blood aspirated by the left ventricle (LV) generates an asymmetric toroidal vortex whose development has been quantified using vortex formation time (VFT), a dimensionless index defined by the length-to-diameter ratio of the aspirated (equivalent cylindrical) fluid column. Since LV wall motion generates the atrioventricular pressure gradient resulting in the early transmitral flow (Doppler E-wave) and associated vortex formation, we hypothesized that the causal relation between VFT and diastolic function (DF), parametrized by stiffness, relaxation, and load, can be elucidated via kinematic modeling. Gharib et al. (Gharib M, Rambod E, Kheradvar A, Sahn DJ, Dabiri JO. Proc Natl Acad Sci USA 103: 6305–6308, 2006) approximated E-wave shape as a triangle and calculated VFTGharib as triangle (E-wave) area (cm) divided by peak (Doppler M-mode derived) mitral orifice diameter (cm). We used a validated kinematic model of filling for the E-wave as a function of time, parametrized by stiffness, viscoelasticity, and load. To calculate VFTkinematic, we computed the curvilinear E-wave area (using the kinematic model) and divided it by peak effective orifice diameter. The derived VFT-to-LV early rapid filling relation predicts VFT to be a function of peak E-wave-to-peak mitral annular tissue velocity (Doppler E′-wave) ratio as (E/E′)3/2. Validation utilized 262 cardiac cycles of simultaneous echocardiographic high-fidelity hemodynamic data from 12 subjects. VFTGharib and VFTkinematic were calculated for each subject and were well-correlated ( R2 = 0.66). In accordance with prediction, VFTkinematic to (E/E′)3/2 relationship was validated ( R 2 = 0.63). We conclude that VFTkinematic is a DF index computable in terms of global kinematic filling parameters of stiffness, viscoelasticity, and load. Validation of the fluid mechanics-to-chamber kinematics relation unites previously unassociated DF assessment methods and elucidates the mechanistic basis of the strong correlation between VFT and (E/E′)3/2.

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Muzio, Francesco Paolo Lo, Giacomo Rozzi, Stefano Rossi, Giovanni Battista Luciani, Ruben Foresti, Aderville Cabassi, Lorenzo Fassina et Michele Miragoli. « Supervised machine learning classifiers and cardiac kinematics support decision-making during open-chest surgery of Tetralogy of Fallot patients ». Vascular Pharmacology 146 (octobre 2022) : 107053. http://dx.doi.org/10.1016/j.vph.2022.107053.

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Gao, Hao, Andrej Aderhold, Kenneth Mangion, Xiaoyu Luo, Dirk Husmeier et Colin Berry. « Changes and classification in myocardial contractile function in the left ventricle following acute myocardial infarction ». Journal of The Royal Society Interface 14, n^o 132 (juillet 2017) : 20170203. http://dx.doi.org/10.1098/rsif.2017.0203.

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In this research, we hypothesized that novel biomechanical parameters are discriminative in patients following acute ST-segment elevation myocardial infarction (STEMI). To identify these biomechanical biomarkers and bring computational biomechanics ‘closer to the clinic’, we applied state-of-the-art multiphysics cardiac modelling combined with advanced machine learning and multivariate statistical inference to a clinical database of myocardial infarction. We obtained data from 11 STEMI patients (ClinicalTrials.gov NCT01717573) and 27 healthy volunteers, and developed personalized mathematical models for the left ventricle (LV) using an immersed boundary method. Subject-specific constitutive parameters were achieved by matching to clinical measurements. We have shown, for the first time, that compared with healthy controls, patients with STEMI exhibited increased LV wall active tension when normalized by systolic blood pressure, which suggests an increased demand on the contractile reserve of remote functional myocardium. The statistical analysis reveals that the required patient-specific contractility, normalized active tension and the systolic myofilament kinematics have the strongest explanatory power for identifying the myocardial function changes post-MI. We further observed a strong correlation between two biomarkers and the changes in LV ejection fraction at six months from baseline (the required contractility ( r = − 0.79, p < 0.01) and the systolic myofilament kinematics ( r = 0.70, p = 0.02)). The clinical and prognostic significance of these biomechanical parameters merits further scrutinization.

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Imbrie-Moore, Annabel M., Matthew H. Park, Michael J. Paulsen, Mark Sellke, Rohun Kulkami, Hanjay Wang, Yuanjia Zhu et al. « Biomimetic six-axis robots replicate human cardiac papillary muscle motion : pioneering the next generation of biomechanical heart simulator technology ». Journal of The Royal Society Interface 17, n^o 173 (décembre 2020) : 20200614. http://dx.doi.org/10.1098/rsif.2020.0614.

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Papillary muscles serve as attachment points for chordae tendineae which anchor and position mitral valve leaflets for proper coaptation. As the ventricle contracts, the papillary muscles translate and rotate, impacting chordae and leaflet kinematics; this motion can be significantly affected in a diseased heart. In ex vivo heart simulation, an explanted valve is subjected to physiologic conditions and can be adapted to mimic a disease state, thus providing a valuable tool to quantitatively analyse biomechanics and optimize surgical valve repair. However, without the inclusion of papillary muscle motion, current simulators are limited in their ability to accurately replicate cardiac biomechanics. We developed and implemented image-guided papillary muscle (IPM) robots to mimic the precise motion of papillary muscles. The IPM robotic system was designed with six degrees of freedom to fully capture the native motion. Mathematical analysis was used to avoid singularity conditions, and a supercomputing cluster enabled the calculation of the system's reachable workspace. The IPM robots were implemented in our heart simulator with motion prescribed by high-resolution human computed tomography images, revealing that papillary muscle motion significantly impacts the chordae force profile. Our IPM robotic system represents a significant advancement for ex vivo simulation, enabling more reliable cardiac simulations and repair optimizations.

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Cutugno, Salvatore, Valentina Agnese, Giovanni Gentile, Giuseppe M. Raffa, Andrew D. Wisneski, Julius M. Guccione, Michele Pilato et Salvatore Pasta. « Patient-Specific Analysis of Ascending Thoracic Aortic Aneurysm with the Living Heart Human Model ». Bioengineering 8, n^o 11 (4 novembre 2021) : 175. http://dx.doi.org/10.3390/bioengineering8110175.

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In ascending thoracic aortic aneurysms (ATAAs), aneurysm kinematics are driven by ventricular traction occurring every heartbeat, increasing the stress level of dilated aortic wall. Aortic elongation due to heart motion and aortic length are emerging as potential indicators of adverse events in ATAAs; however, simulation of ATAA that takes into account the cardiac mechanics is technically challenging. The objective of this study was to adapt the realistic Living Heart Human Model (LHHM) to the anatomy and physiology of a patient with ATAA to assess the role of cardiac motion on aortic wall stress distribution. Patient-specific segmentation and material parameter estimation were done using preoperative computed tomography angiography (CTA) and ex vivo biaxial testing of the harvested tissue collected during surgery. The lumped-parameter model of systemic circulation implemented in the LHHM was refined using clinical and echocardiographic data. The results showed that the longitudinal stress was highest in the major curvature of the aneurysm, with specific aortic quadrants having stress levels change from tensile to compressive in a transmural direction. This study revealed the key role of heart motion that stretches the aortic root and increases ATAA wall tension. The ATAA LHHM is a realistic cardiovascular platform where patient-specific information can be easily integrated to assess the aneurysm biomechanics and potentially support the clinical management of patients with ATAAs.

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de Tullio, M. D., G. Pascazio, L. Weltert, R. De Paulis et R. Verzicco. « Evaluation of prosthetic-valved devices by means of numerical simulations ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 369, n^o 1945 (28 juin 2011) : 2502–9. http://dx.doi.org/10.1098/rsta.2010.0365.

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The in vivo evaluation of prosthetic device performance is often difficult, if not impossible. In particular, in order to deal with potential problems such as thrombosis, haemolysis, etc., which could arise when a patient undergoes heart valve replacement, a thorough understanding of the blood flow dynamics inside the devices interacting with natural or composite tissues is required. Numerical simulation, combining both computational fluid and structure dynamics, could provide detailed information on such complex problems. In this work, a numerical investigation of the mechanics of two composite aortic prostheses during a cardiac cycle is presented. The numerical tool presented is able to reproduce accurately the flow and structure dynamics of the prostheses. The analysis shows that the vortical structures forming inside the two different grafts do not influence the kinematics of a bileaflet valve or the main coronary flow, whereas major differences are present for the stress status near the suture line of the coronaries to the prostheses. The results are in agreement with in vitro and in vivo observations found in literature.

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Ilewicz, Grzegorz, et Edyta Ładyżyńska-Kozdraś. « Specifying Inputs for the Computational Structure of a Surgical System via Optical Method and DLT Algorithm Based on In Vitro Experiments on Cardiovascular Tissue in Minimally Invasive and Robotic Surgery ». Sensors 22, n^o 6 (17 mars 2022) : 2335. http://dx.doi.org/10.3390/s22062335.

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With the application of four optical CMOS sensors, it was possible to capture the trajectory of an endoscopic tool during an in vitro surgical experiment on a cardiovascular preparation. This was due to the possibility of obtaining a path when a reflective marker was attached. In the work, APAS (Ariel Performance Analysis System) software and DLT (direct linear transformation) algorithm were used. This made it possible to acquire kinematic inputs to the computational model of dynamics, which enabled, regardless of the type of surgical robot structure, derivation of the analogous motion of an endoscopic effector due to the mathematical transformation of the trajectory to joints coordinates. Experiments were carried out with the participation of a practiced cardiac surgeon employing classic endoscopic instruments and robot surgical systems. The results indicated by the experiment showed that the inverse task of kinematics of position for the surgical robot with RCM (remote center of motion) structure was solved. The achieved results from the experiment were used as inputs for deriving a numerical dynamics model of surgical robot during transient states that was obtained by applying the finite element method and by driving dynamics moments acquired through the block diagrams method using a steering system with DC (direct current) motor and PID (proportional–integral–derivative) controller. The results section illustrates the course of kinematic values of endoscopic tools which were employed to apply numerical models as inputs, the course of the driving torque of the model of the surgical robot that enabled the selection of the drive system and the strength values, stresses and displacements according to von Mises hypothesis in its structure during the analysis of transient states that made it possible to establish the strength safety of the surgical robot. For the conducted experiments, the accuracy was ±2 [mm]. In the paper, the employment of optical CMOS sensors in surgical robotics and endoscopy is discussed. The paper concludes that the usage of optical sensors for determining inputs for numerical models of dynamics of surgical robots provides the basis for setting the course of physical quantities that appear in their real object structure, in manners close to reality.

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Dickson, Kathryn A., Jeanine M. Donley, Chugey Sepulveda et Lisa Bhoopat. « Effects of temperature on sustained swimming performance and swimming kinematics of the chub mackerelScomber japonicus ». Journal of Experimental Biology 205, n^o 7 (1 avril 2002) : 969–80. http://dx.doi.org/10.1242/jeb.205.7.969.

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SUMMARYThe effects of a 6°C difference in water temperature on maximum sustained swimming speed, swimming energetics and swimming kinematics were measured in the chub mackerel Scomber japonicus (Teleostei:Scombridae), a primarily coastal, pelagic predator that inhabits subtropical and temperate transition waters of the Atlantic, Pacific and Indian Oceans. New data for chub mackerel acclimated to 18°C are compared with published data from our laboratory at 24°C. Twelve individuals acclimated to each of two temperatures (15.6-26.3 cm fork length, FL, and 34-179g at 18°C; 14.0-24.7 cm FL and 26-156g at 24°C) swam at a range of speeds in a temperature-controlled Brett-type respirometer, at the respective acclimation temperature. At a given fish size, the maximum speed that S. japonicus was able to maintain for a 30-min period, while swimming steadily using slow, oxidative locomotor muscle (Umax,c),was significantly greater at 24 than at 18°C (52.5-97.5 cm s-1at 18°C and 70-120 cm s-1 at 24°C). At a given speed and fish size, the rate of oxygen consumption(V̇O2) was significantly higher at 24 than at 18°C because of a higher net cost of transport (1073-4617 J km-1 kg-1 at 18°C and 2708-14895 J km-1 kg-1 at 24°C). Standard metabolic rate, calculated by extrapolating the logV̇O2versus swimming speed relationship to zero speed, did not vary significantly with temperature or fish mass (126.4±67.2 mg O2 h-1 kg-1 at 18°C and 143.2±80.3 mg O2 h-1 kg-1 at 24°C; means ±S.D., N=12). Swimming kinematics was quantified from high-speed (120 Hz) video recordings analyzed with a computerized, two-dimensional motion-analysis system. At a given speed and fish size, there were no significant effects of temperature on tail-beat frequency, tail-beat amplitude or stride length, but propulsive wavelength increased significantly with temperature as a result of an increase in propulsive wave velocity. Thus, the main effects of temperature on chub mackerel swimming were increases in both Umax,c and the net cost of swimming at 24°C. Like other fishes, S. japonicus apparently must recruit more slow,oxidative muscle fibers to swim at a given sustainable speed at the lower temperature because of the reduced power output. Thus, the 24°C mackerel reach a higher speed before they must recruit the fast, glycolytic fibers,thereby increasing Umax,c at 24°C. By quantifying in vivo the effects of temperature on the swimming performance of an ectothermic species that is closely related to the endothermic tunas, this study also provides evidence that maintaining the temperature of the slow,oxidative locomotor muscle at 6°C or more above ambient water temperature in tunas should significantly increase sustainable swimming speeds, but also increase the energetic cost of swimming, unless cardiac output limits muscle performance.

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Rozzi, G., F. Ranieri, S. Rossi, A. Buccarello, L. Fassina, E. Macchi et M. Miragoli. « Novel evaluation of cardiac kinematics/dynamics parameters for in-situ heart by a high-speed bright-field video mapping validated by epicardial multiple lead recording ». Vascular Pharmacology 75 (décembre 2015) : 68–69. http://dx.doi.org/10.1016/j.vph.2015.11.070.

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Lo Muzio, Francesco Paolo, Giacomo Rozzi, Stefano Rossi, Giovanni Battista Luciani, Ruben Foresti, Aderville Cabassi, Lorenzo Fassina et Michele Miragoli. « Artificial Intelligence Supports Decision Making during Open-Chest Surgery of Rare Congenital Heart Defects ». Journal of Clinical Medicine 10, n^o 22 (16 novembre 2021) : 5330. http://dx.doi.org/10.3390/jcm10225330.

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The human right ventricle is barely monitored during open-chest surgery due to the absence of intraoperative imaging techniques capable of elaborating its complex function. Accordingly, artificial intelligence could not be adopted for this specific task. We recently proposed a video-based approach for the real-time evaluation of the epicardial kinematics to support medical decisions. Here, we employed two supervised machine learning algorithms based on our technique to predict the patients’ outcomes before chest closure. Videos of the beating hearts were acquired before and after pulmonary valve replacement in twelve Tetralogy of Fallot patients and recordings were properly labeled as the “unhealthy” and “healthy” classes. We extracted frequency-domain-related features to train different supervised machine learning models and selected their best characteristics via 10-fold cross-validation and optimization processes. Decision surfaces were built to classify two additional patients having good and unfavorable clinical outcomes. The k-nearest neighbors and support vector machine showed the highest prediction accuracy; the patients’ class was identified with a true positive rate ≥95% and the decision surfaces correctly classified the additional patients in the “healthy” (good outcome) or “unhealthy” (unfavorable outcome) classes. We demonstrated that classifiers employed with our video-based technique may aid cardiac surgeons in decision making before chest closure.

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Wangwittayakul, Visit, Thanainit Chotanaphuti, Saradej Khuangsirikul et Songpol Trakulngernthai. « THE EFFECT OF A TOURNIQUET ON INTRAOPERATIVE SOFT TISSUE BALANCE IN CAS TOTAL KNEE ARTHROPLASTY ». Journal of Southeast Asian Medical Research 2, n^o 2 (26 décembre 2018) : 92–97. http://dx.doi.org/10.55374/jseamed.v2i2.14.

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Background: The acquirement of appropriate soft tissue balancing and accurate alignment is an essential procedure in total knee arthroplasty (TKA). Gap balancing affects the final knee kinematics , and inadequate correction of soft tissue imbalances is considered an important factor for early TKA failure. During total knee arthroplasty (TKA), tourniquets are widely used to provide clear visualization of the tissue. The aim of the present study was to evaluate the effect of a tourniquet on intraoperative soft tissue balance in CAS total knee arthroplasty. Method: In this prospective cohort study , patients were eligible for inclusion when they were scheduled for primary CAS TKA due to osteoarthritis , age between 50 and 75 years. Exclusion criteria were severe cardiac complaints , severe pulmonary disorders, Body Mass Index(BMD) > 35,severe coagulation disorder. Thirty knees operated by TKA using a navigation-assisted system (KICK system, DuPuy) were evaluated the soft tissue tension and compared between the tourniquet released and the tourniquet inflated in full extension (0°) and at 90° knee flexion. Result: In total, 30 consecutive patients undergoing CAS TKA met the inclusion criteria. There were differences but not statistically significant in terms of soft tissue tension in knee full extension medial side (p=0.616) , knee, full extension lateral side(p=0.780) , 90° knee flexion medial side (p=0.573) and 90° knee flexion lateral side (p=0.163) Conclusion: Our preliminary results showed that tourniquet application during CAS TKA did not significantly affect the soft tissue balance.

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Lemire, Marcel, Romain Remetter, Thomas J. Hureau, Bernard Geny, Evelyne Lonsdorfer, Fabrice Favret et Stéphane P. Dufour. « Energy Cost of Running in Well-Trained Athletes : Toward Slope-Dependent Factors ». International Journal of Sports Physiology and Performance 17, n^o 3 (1 mars 2022) : 423–31. http://dx.doi.org/10.1123/ijspp.2021-0047.

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Purpose: This study aimed to determine the contribution of metabolic, cardiopulmonary, neuromuscular, and biomechanical factors to the energy cost (ECR) of graded running in well-trained runners. Methods: Eight men who were well-trained trail runners (age: 29 [10] y, mean [SD]; maximum oxygen consumption: 68.0 [6.4] mL·min−1·kg−1) completed maximal isometric evaluations of lower limb extensor muscles and 3 randomized trials on a treadmill to determine their metabolic and cardiovascular responses and running gait kinematics during downhill (DR: −15% slope), level (0%), and uphill running (UR: 15%) performed at similar O2 uptake (approximately 60% maximum oxygen consumption). Results: Despite similar O2 demand, ECR was lower in DR versus level running versus UR (2.5 [0.2] vs 3.6 [0.2] vs 7.9 [0.5] J·kg−1·m−1, respectively; all P < .001). Energy cost of running was correlated between DR and level running conditions only (r2 = .63; P = .018). Importantly, while ECR was correlated with heart rate, cardiac output, and arteriovenous O2 difference in UR (all r2 > .50; P < .05), ECR was correlated with lower limb vertical stiffness, ground contact time, stride length, and step frequency in DR (all r2 > .58; P < .05). Lower limb isometric extension torques were not related to ECR whatever the slope. Conclusion: The determining physiological factors of ECR might be slope specific, mainly metabolic and cardiovascular in UR versus mainly neuromuscular and mechanical in DR. This possible slope specificity of ECR during incline running opens the way for the implementation of differentiated physiological evaluations and training strategies to optimize performance in well-trained trail runners.

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Battista, Nicholas, Dylan Douglas, Andrea Lane, Leigh Samsa, Jiandong Liu et Laura Miller. « Vortex Dynamics in Trabeculated Embryonic Ventricles ». Journal of Cardiovascular Development and Disease 6, n^o 1 (22 janvier 2019) : 6. http://dx.doi.org/10.3390/jcdd6010006.

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Proper heart morphogenesis requires a delicate balance between hemodynamic forces, myocardial activity, morphogen gradients, and epigenetic signaling, all of which are coupled with genetic regulatory networks. Recently both in vivo and in silico studies have tried to better understand hemodynamics at varying stages of veretebrate cardiogenesis. In particular, the intracardial hemodynamics during the onset of trabeculation is notably complex—the inertial and viscous fluid forces are approximately equal at this stage and small perturbations in morphology, scale, and steadiness of the flow can lead to significant changes in bulk flow structures, shear stress distributions, and chemical morphogen gradients. The immersed boundary method was used to numerically simulate fluid flow through simplified two-dimensional and stationary trabeculated ventricles of 72, 80, and 120 h post fertilization wild type zebrafish embryos and ErbB2-inhibited embryos at seven days post fertilization. A 2D idealized trabeculated ventricular model was also used to map the bifurcations in flow structure that occur as a result of the unsteadiness of flow, trabeculae height, and fluid scale ( R e ). Vortex formation occurred in intertrabecular regions for biologically relevant parameter spaces, wherein flow velocities increased. This indicates that trabecular morphology may alter intracardial flow patterns and hence ventricular shear stresses and morphogen gradients. A potential implication of this work is that the onset of vortical (disturbed) flows can upregulate Notch1 expression in endothelial cells in vivo and hence impacts chamber morphogenesis, valvulogenesis, and the formation of the trabeculae themselves. Our results also highlight the sensitivity of cardiac flow patterns to changes in morphology and blood rheology, motivating efforts to obtain spatially and temporally resolved chamber geometries and kinematics as well as the careful measurement of the embryonic blood rheology. The results also suggest that there may be significant changes in shear signalling due to morphological and mechanical variation across individuals and species.

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Nastenko, Ievgen, Vitaliy Maksymenko, Sergiy Potashev, Volodymyr Pavlov, Vitalii Babenko, Sergiy Rysin, Oleksandr Matviichuk et Vasil Lazoryshinets. « Random Forest Algorithm Construction for the Diagnosis of Coronary Heart Disease Based on Echocardiography Video Data Streams ». Innovative Biosystems and Bioengineering 5, n^o 1 (6 avril 2021) : 61–69. http://dx.doi.org/10.20535/ibb.2021.5.1.225794.

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Background. Recent studies show that cardiovascular diseases, including coronary heart disease, are the leading causes of death and one of the main factors of disability worldwide. The detection of cases of this type of disease over the past 30 years has increased from 271 million to 523 million and the number of deaths – from 12.1 million to 18.6 million. Cardiovascular diseases are the main cause of death among the population of Ukraine and, according to this indicator, the country remains one of the world leaders. Coronary heart disease is the leading factor in the loss of health in Ukraine and modern diagnostic methods, including machine learning algorithms, are increasingly being used for timely detection. Objective. According to the data of speckle-tracking echocardiography using the random forest method, construct classification algorithms for diagnosing violations of the kinematics of left ventricular contractions in patients with coronary heart disease at rest, and when using an echostress test with a dobutamine test. Methods. Speckle-tracking echocardiography was used to examine 40 patients with coronary heart disease and 16 in whom no cardiac pathology was found. Echocardiography was recorded in B mode in three positions: along the long axis, in 4-chamber, and 2-chamber positions. In total, 6245 frames of the video stream were used: 1871 – without cardiac abnormalities, and 4374 – in the presence of pathology during the examination. 56 patients (2509 frames of video data) were examined without the use of a dobutamine test and 38 patients (3736 frames of video data) – using an echostress test with a dobutamine test if no disturbances were found at rest. Dobutamine doses of 10, 20, and 40 mcg were administered under the supervision of an anesthesiologist. The data of texture analysis of images were used as informative features. To build an algorithm for detecting coronary heart disease the random forest algorithm was applied. Results. At the first stage of the study, the diagnostic algorithms norma–pathology for the state of rest and dobutamine doses of 10, 20, and 40 mcg were constructed. Before applying the algorithm the samples were randomly divided into training (70%) and test (30%). The classifiers were evaluated for accuracy, sensitivity, and specificity. According to the test samples, the accuracy of diagnostic conclusions varied from 97 to 99%. At the second stage of the study, to increase the versatility of the models, the classifier was built for all images, without dividing them into dobutamine doses. The accuracy for the test samples also ranged from 96.6 to 97.8%. To construct diagnostic algorithms by the random forest method the data of texture analysis of images were used. Conclusions. High-precision classification models were obtained using the random forest algorithm. The developed models can be applied to the analysis of echocardiograms obtained in B mode on equipment that is not equipped with the speckle tracking technology.

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Mocan, Bogdan, Claudiu Schonstein, Calin Neamtu, Mircea Murar, Mircea Fulea, Radu Comes et Mihaela Mocan. « CardioVR-ReTone—Robotic Exoskeleton for Upper Limb Rehabilitation following Open Heart Surgery : Design, Modelling, and Control ». Symmetry 14, n^o 1 (5 janvier 2022) : 81. http://dx.doi.org/10.3390/sym14010081.

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Following cardiac surgery, patients experience difficulties with the rehabilitation process, often finding it difficult, and therefore lack the motivation for rehabilitation activities. As the number of people aged 65 and over will rise by 207 percent globally by 2050, the need for cardiac rehabilitation will significantly increase, as this is the main population to experience heart problems. To address this challenge, this paper proposes a new robotic exoskeleton concept with 12 DoFs (6 DoFs on each arm), with a symmetrical structure for the upper limbs, to be used in the early rehabilitation of cardiac patients after open-heart surgery. The electromechanical design (geometric, kinematic, and dynamic model), the control architecture, and the VR-based operating module of the robotic exoskeleton are presented. To solve the problem of the high degree of complexity regarding the CardioVR-ReTone kinematic and dynamic model, the iterative algorithm, kinetic energy, and generalized forces were used. The results serve as a complete model of the exoskeleton, from a kinematic and dynamic point of view as well as to the selection of the electric motors, control system, and VR motivation model. The validation of the concept was achieved by evaluating the exoskeleton structure from an ergonomic point of view, emphasizing the movements that will be part of the cardiac rehabilitation.

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Langer, John. « Regression Analysis of the Left-ventricular Isochoric Pressure Decay of the Heart : Four or Five Model Parameters ? » International Cardiovascular Forum Journal 4 (4 décembre 2015) : 53. http://dx.doi.org/10.17987/icfj.v4i0.168.

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BACKGROUND: Isochoric (isovolumic) cardiac pressure decay data were previously described by a four-parametric logistic (tangens hyperbolicus) regression model (Langer model). However, a five-parametric kinematic model (Chung model), according to the differential equation of damped oscillation, was recently introduced to describe the isochoric pressure fall. The present study clarifies (a/) whether these five parameters can be reliably estimated from empirical pressure decay data and if the model excels the four-parametric one, and (b/) whether the kinematic Chung model validly describes these pressure decays. METHODS: High-fidelity intraventricular pressure decay data from 1203 isolated working guinea pig and rat hearts were analyzed by both models. RESULTS: Most cases present with a higher regression error in the five-parametric kinematic model, the median ratio (F value) of its regression variance by those of the four-parametric logistic model is 1.004 (95 per cent confidence interval: 1.002 to 1.006) in in the guinea pig as well as in the rat group. Additionally, the parameters of both models were estimated from the first and second half of the decay phase separately to check for the models' validity. The five-parametric model yields significantly non-constant parameters more often than the four-parametric model. CONCLUSION: (a) the five parameters of the kinematic Chung model remain underdetermined by the empirical pressure data, and {b) this five-parametric model does not provide a valid description of the isochoric cardiac pressure decay.

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Mayer, Hermann, Istvan Nagy, Alois Knoll, Eva U. Braun, Robert Bauernschmitt et Rüdiger Lange. « Haptic Feedback in a Telepresence System for Endoscopic Heart Surgery ». Presence : Teleoperators and Virtual Environments 16, n^o 5 (1 octobre 2007) : 459–70. http://dx.doi.org/10.1162/pres.16.5.459.

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The implementation of telemanipulator systems for cardiac surgery enabled heart surgeons to perform delicate minimally invasive procedures with high precision under stereoscopic view. At present, commercially available systems do not provide force-feedback or Cartesian control for the operating surgeon. The lack of haptic feedback may cause damage to tissue and can cause breaks of suture material. In addition, minimally invasive procedures are very tiring for the surgeon due to the need for visual compensation for the missing force feedback. While a lack of Cartesian control of the end effectors is acceptable for surgeons (because every movement is visually supervised), it prevents research on partial automation. In order to improve this situation, we have built an experimental telemanipulator for endoscopic surgery that provides both force-feedback (in order to improve the feeling of immersion) and Cartesian control as a prerequisite for automation. In this article, we focus on the inclusion of force feedback and its evaluation. We completed our first bimanual system in early 2003 (EndoPAR Endoscopic Partial Autonomous Robot). Each robot arm consists of a standard robot and a surgical instrument, hence providing eight DOF that enable free manipulation via trocar kinematics. Based on the experience with this system, we introduced an improved version in early 2005. The new ARAMIS system (Autonomous Robot Assisted Minimally Invasive Surgery) has four multi-purpose robotic arms mounted on a gantry above the working space. Again, the arms are controlled by two force-feedback devices, and 3D vision is provided. In addition, all surgical instruments have been equipped with strain gauge force sensors that can measure forces along all translational directions of the instrument's shaft. Force-feedback of this system was evaluated in a scenario of robotic heart surgery, which offers an impression very similar to the standard, open procedures with high immersion. It enables the surgeon to palpate arteriosclerosis, to tie surgical knots with real suture material, and to feel the rupture of suture material. Therefore, the hypothesis that haptic feedback in the form of sensory substitution facilitates performance of surgical tasks was evaluated on the experimental platform described in the article (on the EndoPAR version). In addition, a further hypothesis was explored: The high fatigue of surgeons during and after robotic operations may be caused by visual compensation due to the lack of force-feedback (Thompson, J., Ottensmeier, M., & Sheridan, T. 1999. Human Factors in Telesurgery, Telmed Journal, 5 (2) 129–137.).

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Ijiri, Takashi, Takashi Ashihara, Nobuyuki Umetani, Takeo Igarashi, Ryo Haraguchi, Hideo Yokota et Kazuo Nakazawa. « A Kinematic Approach for Efficient and Robust Simulation of the Cardiac Beating Motion ». PLoS ONE 7, n^o 5 (30 mai 2012) : e36706. http://dx.doi.org/10.1371/journal.pone.0036706.

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Mossahebi, Sina, Leonid Shmuylovich et Sándor J. Kovács. « The thermodynamics of diastole : kinematic modeling-based derivation of the P-V loop to transmitral flow energy relation with in vivo validation ». American Journal of Physiology-Heart and Circulatory Physiology 300, n^o 2 (février 2011) : H514—H521. http://dx.doi.org/10.1152/ajpheart.00814.2010.

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Pressure-volume (P-V) loop-based analysis facilitates thermodynamic assessment of left ventricular function in terms of work and energy. Typically these quantities are calculated for a cardiac cycle using the entire P-V loop, although thermodynamic analysis may be applied to a selected phase of the cardiac cycle, specifically, diastole. Diastolic function is routinely quantified by analysis of transmitral Doppler E-wave contours. The first law of thermodynamics requires that energy (ε) computed from the Doppler E-wave (εE-wave) and the same portion of the P-V loop (εP-V E-wave) be equivalent. These energies have not been previously derived nor have their predicted equivalence been experimentally validated. To test the hypothesis that εP-V E-wave and εE-wave are equivalent, we used a validated kinematic model of filling to derive εE-wave in terms of chamber stiffness, relaxation/viscoelasticity, and load. For validation, simultaneous (conductance catheter) P-V and echocadiographic data from 12 subjects (205 total cardiac cycles) having a range of diastolic function were analyzed. For each E-wave, εE-wave was compared with εP-V E-wave calculated from simultaneous P-V data. Linear regression yielded the following: εP-V E-wave = αεE-wave + b ( R2 = 0.67), where α = 0.95 and b = 6 e−5. We conclude that E-wave-derived energy for suction-initiated early rapid filling εE-wave, quantitated via kinematic modeling, is equivalent to invasive P-V-defined filling energy. Hence, the thermodynamics of diastole via εE-wave generate a novel mechanism-based index of diastolic function suitable for in vivo phenotypic characterization.

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Shi, Pengcheng, et Huafeng Liu. « Stochastic finite element framework for simultaneous estimation of cardiac kinematic functions and material parameters ». Medical Image Analysis 7, n^o 4 (décembre 2003) : 445–64. http://dx.doi.org/10.1016/s1361-8415(03)00066-5.

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Bishop, C., et P. Butler. « Physiological modelling of oxygen consumption in birds during flight ». Journal of Experimental Biology 198, n^o 10 (1 octobre 1995) : 2153–63. http://dx.doi.org/10.1242/jeb.198.10.2153.

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This study combines data on changes in cardiovascular variables with body mass (Mb) and with exercise intensity to model the oxygen supply available to birds during flight. Its main purpose is to provide a framework for identifying the factors involved in limiting aerobic power input to birds during flight and to suggest which cardiovascular variables are the most likely to have been influenced by natural selection when considering both allometric and adaptive variation. It is argued that natural selection has acted on heart rate (fh) and cardiac stroke volume (Vs), so that the difference in the arteriovenous oxygen content (CaO2-Cv¯O2) in birds, both at rest and during flight, is independent of Mb. Therefore, the Mb exponent for oxygen consumption (V(dot)O2) during flight can be estimated from measurements of heart rate and stroke volume. Stroke volume is likely to be directly proportional to heart mass (Mh) and, using empirical data, values for the Mb coefficients and exponents of various cardiovascular variables are estimated. It is concluded that, as found for mammals, fh is the main adaptive variable when considering allometric variation, although Mh also shows a slight scaling effect. Relative Mh is likely to be the most important when considering adaptive specialisations. The Fick equation may be represented as: (V(dot)O2)Mbz = (fh)Mbw x (Vs)Mbx x (CaO2 - Cv¯O2)Mby , where w, x, y, z are the body mass exponents for each variable and the terms in parentheses represent the Mb coefficients. Utilising this formula and data from the literature, the scaling of minimum V(dot)O2 during flight for bird species with a 'high aerobic capacity' (excluding hummingbirds) is calculated to be: 166Mb0.77±0.09 = 574Mb-0.19±0.02 x 3.48Mb0.96±0.02 x 0.083Mb0.00±0.05 , and for hummingbirds (considered separately owing to their unique wing kinematics) it is: 314Mb0.90±0.22 = 617Mb-0.10±0.06 x 6.13Mb1.00±0.11 x 0.083Mb0.00±0.05 . These results are largely dependent on the cardiovascular values obtained from pigeons flying near to the minimum power speed of 10 m s-1, but would appear to provide realistic values. Both the measured and the estimated V(dot)O2 for hummingbirds appear to scale with a larger Mb exponent than that for all other birds, and it is suggested that this is as a result of the larger Mb exponent for flight muscle mass as the larger species of hummingbirds try to maintain hovering performance. It is proposed that estimated V(dot)O2 for birds during flight, which is based on Mh in combination with estimates of fh and CaO2-Cv¯O2, gives an indirect measure of relative aerobic power input and, when corrected for the estimated scaling influences of the mechano-chemical conversion efficiency and lift generation with respect to Mb, may be a useful indicator of the relative capacity of the muscle to sustain power output and lift production during flight.

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Yedukondalu, G., Sajjan Patnaik, P. Lakshmi Venkatesh et S. Siva Jagadeesh. « Chest compression with 2-DOF parallel manipulator for cardiopulmonary resuscitation ». International Journal of Engineering & ; Technology 7, n^o 2.8 (19 mars 2018) : 211. http://dx.doi.org/10.14419/ijet.v7i2.8.10411.

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Chest compression process is used for recovering patients who met with a cardiac arrest in emergency situations. Chest compression is the only possibility of rescuing patients during cardiopulmonary resuscitation (CPR). It is hard to achieve the exact chest compression’s depth and rate even by experienced professionals as per the CPR guideline. A 2-DOF 2-RRR translational parallel manipulator was designed for delivering chest compressions. The kinematic analysis is carried out analytically.The workspace of the manipulator is examined in consideration of physical constraints imposed by joints. Finally, the manipulator operates with exact compression depth and rate during CPR.

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Soleimani, Reza, et Edgar Lobaton. « Enhancing Inference on Physiological and Kinematic Periodic Signals via Phase-Based Interpretability and Multi-Task Learning ». Information 13, n^o 7 (7 juillet 2022) : 326. http://dx.doi.org/10.3390/info13070326.

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Physiological and kinematic signals from humans are often used for monitoring health. Several processes of interest (e.g., cardiac and respiratory processes, and locomotion) demonstrate periodicity. Training models for inference on these signals (e.g., detection of anomalies, and extraction of biomarkers) require large amounts of data to capture their variability, which are not readily available. This hinders the performance of complex inference models. In this work, we introduce a methodology for improving inference on such signals by incorporating phase-based interpretability and other inference tasks into a multi-task framework applied to a generative model. For this purpose, we utilize phase information as a regularization term and as an input to the model and introduce an interpretable unit in a neural network, which imposes an interpretable structure on the model. This imposition helps us in the smooth generation of periodic signals that can aid in data augmentation tasks. We demonstrate the impact of our framework on improving the overall inference performance on ECG signals and inertial signals from gait locomotion.

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Sheehan, Florence H., et R. Eugene Zierler. « Simulation for competency assessment in vascular and cardiac ultrasound ». Vascular Medicine 23, n^o 2 (7 février 2018) : 172–80. http://dx.doi.org/10.1177/1358863x17751656.

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Healthcare providers who use peripheral vascular and cardiac ultrasound require specialized training to develop the technical and interpretive skills necessary to perform accurate diagnostic tests. Assessment of competence is a critical component of training that documents a learner’s progress and is a requirement for competency-based medical education (CBME) as well as specialty certification or credentialing. The use of simulation for CBME in diagnostic ultrasound is particularly appealing since it incorporates both the psychomotor and cognitive domains while eliminating dependency on the availability of live patients with a range of pathology. However, successful application of simulation in this setting requires realistic, full-featured simulators and appropriate standardized metrics for competency testing. The principal diagnostic parameter in peripheral vascular ultrasound is measurement of peak systolic velocity (PSV) on Doppler spectral waveforms, and simulation of Doppler flow detection presents unique challenges. The computer-based duplex ultrasound simulator developed at the University of Washington uses computational fluid dynamics modeling and presents real-time color-flow Doppler images and Doppler spectral waveforms along with the corresponding B-mode images. This simulator provides a realistic scanning experience that includes measuring PSV in various arterial segments and applying actual diagnostic criteria. Simulators for echocardiography have been available since the 1990s and are currently more advanced than those for peripheral vascular ultrasound. Echocardiography simulators are now offered for both transesophageal echo and transthoracic echo. These computer-based simulators have 3D graphic displays that provide feedback to the learner and metrics for assessment of technical skill that are based on transducer tracking data. Such metrics provide a motion-based or kinematic analysis of skill in performing cardiac ultrasound. The use of simulation in peripheral vascular and cardiac ultrasound can provide a standardized and readily available method for training and competency assessment.

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Riordan, Matt M., et Sándor J. Kovács. « Absence of diastolic mitral annular oscillations is a marker for relaxation-related diastolic dysfunction ». American Journal of Physiology-Heart and Circulatory Physiology 292, n^o 6 (juin 2007) : H2952—H2958. http://dx.doi.org/10.1152/ajpheart.01356.2006.

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Although Doppler tissue imaging frequently indicates the presence of mitral annular oscillations (MAO) following the E′ wave (E″ wave, etc.), only recently was it shown that annular “ringing” follows the rules of damped harmonic oscillatory motion. Oscillatory model-based analysis of E′ and E″ waves provides longitudinal left ventricular (LV) stiffness ( k′), relaxation/viscoelasticity ( c′), and stored elastic strain ( xo′) parameters. We tested the hypothesis that presence (MAO+) vs. absence (MAO−) of diastolic MAO is an index of superior LV relaxation by analyzing simultaneous echocardiographic-hemodynamic data from 35 MAO+ and 20 MAO− normal ejection fraction (EF) subjects undergoing cardiac catheterization. Echocardiographic annular motion and transmitral flow data were analyzed with a previously validated kinematic model of filling. Invasive and noninvasive diastolic function (DF) indexes differentiated between MAO+ and MAO− groups. Specifically, the MAO+ group had a shorter time constant of isovolumic relaxation [τ; 51 (SD 13) vs. 67 (SD 27) ms; P < 0.01] and isovolumic relaxation time [63 (SD 16) vs. 82 (SD 17) ms; P < 0.001] and greater ratio of peak E-wave to peak A-wave velocity [1.19 (SD 0.31) vs. 0.97 (SD 0.31); P < 0.05]. The MAO+ group had greater peak lateral mitral annulus velocity [E′; 17.5 (SD 3.1) vs. 13.5 (SD 3.8) cm/s; P < 0.001] and LVEF [71.2 (SD 7.5)% vs. 65.4 (SD 9.1)%; P < 0.05] and lower heart rate [65 (SD 9) vs. 74 (SD 9) beats/min, P < 0.001]. Additional conventional and kinematic modeling-derived indexes were highly concordant with these findings. We conclude that absence of early diastolic MAO is an easily discernible marker for relaxation-related diastolic dysfunction. Quantitation of MAO via stiffness and relaxation/viscoelasticity parameters facilitates quantitative assessment of regional (i.e., longitudinal) DF and may improve diagnosis of diastolic dysfunction.

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Bowman, Andrew W., Paul A. Frihauf et Sándor J. Kovács. « Time-varying effective mitral valve area : prediction and validation using cardiac MRI and Doppler echocardiography in normal subjects ». American Journal of Physiology-Heart and Circulatory Physiology 287, n^o 4 (octobre 2004) : H1650—H1657. http://dx.doi.org/10.1152/ajpheart.00269.2004.

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Precise knowledge of the volume and rate of early rapid left ventricular (LV) filling elucidates kinematic aspects of diastolic physiology. The Doppler E wave velocity-time integral (VTI) is conventionally used as the estimate of early, rapid-filling volume; however, this implicitly requires the assumption of a constant effective mitral valve area (EMVA). We sought to evaluate whether the EMVA is truly constant throughout early, rapid filling in 10 normal subjects using cardiac magnetic resonance imaging (MRI) and contemporaneous Doppler echocardiography, which were synchronized via ECG. LV volume measurements as a function of time were obtained via MRI, and transmitral flow values were measured via Doppler echocardiography. The synchronized data were used to predict EMVA as a function of time during early diastole. Validation involved EMVA determination using 1) the short-axis echocardiographic images near the mitral valve leaflet tips, 2) the distance between leaflet tips in the echocardiographic parasternal long-axis view, and 3) the distance between leaflet tips from the MRI LV outflow tract view. Predicted EMVA values varied substantially during early rapid filling, and observed EMVA values agreed well with predictions. We conclude that the EMVA is not constant, and its variation causes LV volume to increase faster than is reflected by the VTI. These results reveal the mechanism of early rapid volumetric increase and directly affect the significance and physiological interpretation of the VTI of the Doppler E wave. Application to subjects in selected pathophysiological subsets is in progress.

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Bhagavan, Druv, William M. Padovano et Sándor J. Kovács. « Alternative diastolic function models of ventricular longitudinal filling velocity are mathematically identical ». American Journal of Physiology-Heart and Circulatory Physiology 318, n^o 5 (1 mai 2020) : H1059—H1067. http://dx.doi.org/10.1152/ajpheart.00681.2019.

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The spatiotemporal features of normal in vivo cardiac motion are well established. Longitudinal velocity has become a focus of diastolic function (DF) characterization, particularly the tissue Doppler e′-wave, manifesting in early diastole when the left ventricle (LV) is a mechanical suction pump (dP/dV < 0). To characterize DF and elucidate mechanistic features, several models have been proposed and have been previously compared algebraically, numerically, and in their ability to fit physiological velocity data. We analyze two previously noncompared models of early rapid-filling lengthening velocity (Doppler e′-wave): parametrized diastolic filling (PDF) and force balance model (FBM). Our initial numerical experiments sampled FBM-generated e′( t) contours as input to determine PDF model predicted fit. The resulting exact numerical agreement [standard error of regression (SER) = 9.06 × 10−16] was not anticipated. Therefore, we analyzed all published FBM-generated e′( t) contours and observed identical agreement. We re-expressed FBM’s algebraic expressions for e′( t) and observed for the first time that model-based predictions for lengthening velocity by the FBM and the PDF model are mathematically identical: e′( t) = γe−α tsinh(β t), thereby providing exact algebraic relations between the three PDF parameters and the six FBM parameters. Previous pioneering experiments have independently established the unique determinants of e′( t) to be LV relaxation, restoring forces (stiffness), and load. In light of the exact intermodel agreement, we conclude that the three PDF parameters, relaxation, stiffness (restoring forces), and load, are unique determinants of DF and e′( t). Thus, we show that only the PDF formalism can compute the three unique, independent, physiological determinants of long-axis LV myocardial velocity from e′( t). NEW & NOTEWORTHY We show that two separate, independently derived physiological (kinematic) models predict mathematically identical expressions for LV-lengthening velocity (Doppler e′-wave), indicating that damped harmonic oscillatory motion is a physiologically accurate model of diastolic function. Although both models predict the same “overdamped” velocity contour, only one model solves the “inverse problem” and generates unique, lumped parameters of relaxation, stiffness (restoring force), and load from the e′-wave.

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Melczer, Csaba, László Melczer, András Oláh, Mónika Sélleyné-Gyúró, Zsanett Welker et Pongrác Ács. « Telemetry Option in the Measurement of Physical Activity for Patients with Heart Failure ». Practice and Theory in Systems of Education 10, n^o 2 (1 mai 2015) : 209–16. http://dx.doi.org/10.1515/ptse-2015-0020.

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AbstractMeasurement of physical activity among patients with heart failure typically requires a special approach due to the patients’ physical status. Nowadays, a technology is already available that can measure the kinematic movements in 3-D by a pacemaker and implantable defibrillator giving an assessment on software. The telemetry data can be transmitted to a central system. The research aims to elaborate the methods that help to compare of the data concerning physical activity both built-in an accelerometer in Cardiac Resychrinisation Therapy (CRT) devices and data obtained from an external Actigraph GT3XE-Plus Triaxial Activity Monitor. 5 persons participated in the pilot study (n=5); mean age: 57+- 13.37; BMI: 90.6+- 7.63. The Actigraph data from CRT device were examined in a 6-day-interval, between February 28 and March 5, 2014. The investigation started conducting a 6-minute walking test and continued with the measurement of daily physical activity. For data analysis descriptive statistics and linear regression analysis were used. It is clear from the data obtained from Actigraph that the MET values (mean: 1.17 ± 0.096) of the patients in the sample were extremely low due to their disease. However, some patients with higher physical activity than average (1.26; 1.28) seemed to be noteworthy, but they showed lower performance than healthy people. The physical activity of the patients during the 6-minute walking test corresponded to 1.9-2.48 MET. The physical activity of patients was found typically in the “light or moderate range” classifying the physical activity by Actigraph. Data from Actigraph are accurate and detailed making the physical activity of the patients measurable and appreciable. The results of the 6-minute walking test were in the category from moderate to very vigorous for individualized moderate physical performance based on Actigraph. It indicates the individual performance differences among patients. However, the daily physical performance is even lower than that of the 6- minute walking. We can conclude from the data related to the percentage of the average activity in CRT system to the average energy consumption and the improvement in the patients’ physical condition. Due to the limitations of the sampling frequency the different time intervals cannot be isolated in the different intensity ranges. Therefore, the percentage of the data of physical activity provided by the device may have a limited use.

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Bousquet, Jean-Claude, et Gianni Lanzafame. « Nouvelle interpretation des fractures des eruptions laterales de l'Etna ; consequences pour son cadre tectonique ». Bulletin de la Société Géologique de France 172, n^o 4 (1 juillet 2001) : 455–67. http://dx.doi.org/10.2113/172.4.455.

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Abstract Mt Etna is cut by numerous fractures (fissures and faults) of very different origin and orientation. They have been used to define the activity and the tectonic setting of the volcano. After a discussion of the proposed tectonic models for Etna, an examination of the fractures, which are linked to the high flank eruptions, was carried out based on the geological and geophysical studies of the recent eruptions (1983, 1989, 1991-93). All of these surface breaks are of strictly volcanic origin; they open and advance very slowly, in relation to the propagation of the dyke, as well as its width and depth from the volcano surface. If the dyke summit is not too far from the surface (about 200-300 m), fissures and normal faults, arranged in a graben, appear. When the dyke intersects the slope of the volcano, a flank eruption follows. Therefore, these fractures do not have a tectonic or volcano-tectonic origin: they do not cut the entire volcanic edifice, and thus cannot be used to define the rift-zones nor to characterise the tectonic regime controlling the functioning of Etna. They give information on the dyke orientation on the slopes of the volcanic edifice and cannot be used as significative markers of extension [Frazzetta and Villari, 1981; Kieffer 1983a and b; Monaco et al., 1997]. The simultaneous opening of radial fractures, according to various azimuths, is frequent and clearly indicates that, in these cases, the regional stress field is not implicated. But high on Etna, the concentration of flank eruptions, on the eastern side, and the orientation change of the fractures (fig. 6), when they travel away from the summit, have been repeatedly indicated. The repetition of flank eruptions and the azimuth changes can be explained, simply, by the closeness of the Valle del Bove [Murray, 1994], which induces a decrease of the confinement pressure. The dyke emplacements of the summit eruptions cause an eastward displacement of the higher part of Etna. Marine geophysical data indicate that this volcano is, however, not the site of a large scale lateral spreading to the Ionian sea. Consequently, an eastward detachment is present only on the superior part of the volcano (figs. 1B and 7C). In fact, an up to 100 m high and oversteepened east-facing scarp, between the towns of Vena and Presa, extends towards the south for some kilometers [Lanzafame et al., 2000]. It is made up of volcanic rocks affected by strong brecciation. Inverse faults are found in front of the scarp. The base of this one is found at the level of the pre-Etnean clays, which would have helped the displacement of the volcanics. The studies on the tectonic setting in which Etna is located has called the attention of numerous researchers. From the earliest studies, the presence of numerous normal faults has supported the idea that this volcano, as many others, is active in an extensional regime. The most recent geological and geophysical data show a more complex situation. Deep under Etna (more than 10 km), a compressive field (sigma 1 N-S) is present according to focal mechanisms [Cardaci et al.; 1990; Ferrucci et al., 1993; Cocina et al., 1997]. More superficially, instead, extension is usual. The importance of the weight of the volcanic edifice, in the spatial (horizontal and vertical) modification of the compressive stress field, must still be clarified. It is very clear, in any case, that Etna cannot be explained by an extensional regime or kinematics in extension [Monaco et al., 1997] using normal faults, which form during the flank eruptions.

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Liu, Hao, João S. Soares, John Walmsley, David S. Li, Samarth Raut, Reza Avazmohammadi, Paul Iaizzo et al. « The impact of myocardial compressibility on organ-level simulations of the normal and infarcted heart ». Scientific Reports 11, n^o 1 (29 juin 2021). http://dx.doi.org/10.1038/s41598-021-92810-y.

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AbstractMyocardial infarction (MI) rapidly impairs cardiac contractile function and instigates maladaptive remodeling leading to heart failure. Patient-specific models are a maturing technology for developing and determining therapeutic modalities for MI that require accurate descriptions of myocardial mechanics. While substantial tissue volume reductions of 15–20% during systole have been reported, myocardium is commonly modeled as incompressible. We developed a myocardial model to simulate experimentally-observed systolic volume reductions in an ovine model of MI. Sheep-specific simulations of the cardiac cycle were performed using both incompressible and compressible tissue material models, and with synchronous or measurement-guided contraction. The compressible tissue model with measurement-guided contraction gave best agreement with experimentally measured reductions in tissue volume at peak systole, ventricular kinematics, and wall thickness changes. The incompressible model predicted myofiber peak contractile stresses approximately double the compressible model (182.8 kPa, 107.4 kPa respectively). Compensatory changes in remaining normal myocardium with MI present required less increase of contractile stress in the compressible model than the incompressible model (32.1%, 53.5%, respectively). The compressible model therefore provided more accurate representation of ventricular kinematics and potentially more realistic computed active contraction levels in the simulated infarcted heart. Our findings suggest that myocardial compressibility should be incorporated into future cardiac models for improved accuracy.

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Rozzi, Giacomo, Francesco Paolo Lo Muzio, Lorenzo Fassina, Stefano Rossi, Rosario Statello, Camilla Sandrini, Maira Laricchiuta, Giuseppe Faggian, Michele Miragoli et Giovanni Battista Luciani. « Right ventricular functional recovery depends on timing of pulmonary valve replacement in tetralogy of Fallot : a video kinematic study ». European Journal of Cardio-Thoracic Surgery, 6 février 2021. http://dx.doi.org/10.1093/ejcts/ezab026.

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Abstract OBJECTIVES Indications for and timing of pulmonary valve replacement (PVR) after tetralogy of Fallot repair are controversial. Among magnetic resonance imaging indices proposed to time valve replacement, a right ventricular (RV) end-diastolic volume index greater than 160 ml/m2 is often used. Recent evidence suggests that this value may still identify patients with irreversible RV dysfunction, thus hindering recovery. Our goal was to define, using intraoperative video kinematic evaluation, whether a relationship exists between timing of PVR and early functional recovery after surgery. METHODS Between November 2016 and November 2018, a total of 12 consecutive patients aged 27.1 ± 19.1 years underwent PVR on average 22.2 ± 13.3 years after tetralogy of Fallot repair. Mean RV end-diastolic volume evident on the magnetic resonance images was 136.9 ± 35.7 ml/m2. Intraoperative cardiac kinematics were assessed by video kinematic evaluation via a high-speed camera acquiring videos at 200 fps before and after valve replacement. RESULTS Patients presenting with RV end-diastolic volume <147 ml/m2 were significantly younger (11.2 ± 5.0 vs 38.4 ± 17.0; P = 0.005) and had a shorter time interval to valve replacement (11.0 ± 5.2 vs 30.1 ± 11.3; P = 0.03). The entire population showed a moderate correlation among energy expenditure, cardiac fatigue, perimeter of contraction and preoperative RV end-diastolic volume index. Both groups showed a reduction in all kinematic parameters after PVR, but those with end-diastolic volume >147 ml/m2 showed an unpredictable outcome. CONCLUSIONS Video kinematic evaluation provides insight into intraoperative RV recovery in patients with tetralogy of Fallot undergoing PVR. Accordingly, functional recovery can be expected in patients with preoperative end-diastolic volume <147 ml/m2.

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Canè, Federico, Lucas Delcour, Alberto Cesare Luigi Redaelli, Patrick Segers et Joris Degroote. « A CFD study on the interplay of torsion and vortex guidance by the mitral valve on the left ventricular wash-out making use of overset meshes (Chimera technique) ». Frontiers in Medical Technology 4 (22 décembre 2022). http://dx.doi.org/10.3389/fmedt.2022.1018058.

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Cardiovascular disease often occurs with silent and gradual alterations of cardiac blood flow that can lead to the onset of chronic pathological conditions. Image-based patient-specific Computational Fluid Dynamics (CFD) models allow for an extensive quantification of the flow field beyond the direct capabilities of medical imaging techniques that could support the clinicians in the early diagnosis, follow-up, and treatment planning of patients. Nonetheless, the large and impulsive kinematics of the left ventricle (LV) and the mitral valve (MV) pose relevant modeling challenges. Arbitrary Lagrangian-Eulerian (ALE) based computational fluid dynamics (CFD) methods struggle with the complex 3D mesh handling of rapidly moving valve leaflets within the left ventricle (LV). We, therefore, developed a Chimera-based (overset meshing) method to build a patient-specific 3D CFD model of the beating LV which includes a patient-inspired kinematic model of the mitral valve (LVMV). Simulations were performed with and without torsion. In addition, to evaluate how the intracardiac LV flow is impacted by the MV leaflet kinematics, a third version of the model without the MV was generated (LV with torsion). For all model versions, six cardiac cycles were simulated. All simulations demonstrated cycle-to-cycle variations that persisted after six cycles but were albeit marginal in terms of the magnitude of standard deviation of velocity and vorticity which may be related to the dissipative nature of the numerical scheme used. The MV was found to have a crucial role in the development of the intraventricular flow by enhancing the direct flow, the apical washout, and the propagation of the inlet jet towards the apical region. Consequently, the MV is an essential feature in the patient-specific CFD modeling of the LV. The impact of torsion was marginal on velocity, vorticity, wall shear stress, and energy loss, whereas it resulted to be significant in the evaluation of particle residence times. Therefore, including torsion could be considered in patient-specific CFD models of the LV, particularly when aiming to study stasis and residence time. We conclude that, despite some technical limitations encountered, the Chimera technique is a promising alternative for ALE methods for 3D CFD models of the heart that include the motion of valve leaflets.

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Young, Bruce A., et Michael J. Cramberg. « Treadmill locomotion in the American alligator (Alligator mississippiensis) produces dynamic changes in intracranial cerebrospinal fluid pressure ». Scientific Reports 12, n^o 1 (12 juillet 2022). http://dx.doi.org/10.1038/s41598-022-15918-9.

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AbstractTo examine the influence of movement on cerebrospinal fluid (CSF) dynamics, intracranial subdural pressure recordings were taken from sub-adult alligators (Alligator mississippiensis) locomoting on a treadmill. Pressure recordings documenting the cardiac, ventilatory, and barostatic influences on the CSF were in good agreement with previous studies. During locomotion the CSF exhibits sinusoidal patterns of pressure change that spanned a mean amplitude of 56 mm Hg, some 16 × the amplitude of the cardiac-linked pulsations. These sinusoidal CSF pulsations were closely linked to the locomotor kinematics, particularly the lateral oscillations of the alligator’s head. Data recorded from the freely moving alligators suggest that fluid inertia, body cavity pressures, and likely other factors all influence the CSF pressure. The clear relationship between movement and CSF pressure described in this study suggests that the paucity of studies examining human CSF dynamics during movement should be addressed.

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Zhou, J., A. G. Leja, M. Salvatori, D. Della Latta et A. Di Fulvio. « Application of Monte Carlo Algorithms to Cardiac Imaging Reconstruction ». Current Pharmaceutical Design 26 (28 décembre 2020). http://dx.doi.org/10.2174/1381612826999201228215225.

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Abstract:: Monte Carlo algorithms have a growing impact on nuclear medicine reconstruction processes. One of the main limitations of myocardial perfusion imaging (MPI) is the effective mitigation of the scattering component, which is particularly challenging in Single Photon Emission Computed Tomography (SPECT). In SPECT, no timing information can be retrieved to locate the primary source photons. Monte Carlo methods allow an event-by-event simulation of the scattering kinematics, which can be incorporated into a model of the imaging system response. This approach was adopted since the late Nineties by several authors, and recently took advantage of the increased computational power made available by high-performance CPUs and GPUs. These recent developments enable a fast image reconstruction with an improved image quality, compared to deterministic approaches. Deterministic approaches are based on energy-windowing of the detector response, and on the cumulative estimate and subtraction of the scattering component. In this paper, we review the main strategies and algorithms to correct for the scattering effect in SPECT and focus on Monte Carlo developments, which nowadays allow the three-dimensional reconstruction of SPECT cardiac images in a few seconds.

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Toosizadeh, Nima, Maryam Eskandari, Hossein Ehsani, Saman Parvaneh, Mehran Asghari et Nancy Sweitzer. « Frailty assessment using a novel approach based on combined motor and cardiac functions : a pilot study ». BMC Geriatrics 22, n^o 1 (14 mars 2022). http://dx.doi.org/10.1186/s12877-022-02849-3.

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Abstract Background Previous research showed association between frailty and an impaired autonomic nervous system; however, the direct effect of frailty on heart rate (HR) behavior during physical activity is unclear. The purpose of the current study was to determine the association between HR increase and decrease with frailty during a localized upper-extremity function (UEF) task to establish a multimodal frailty test. Methods Older adults aged 65 or older were recruited and performed the UEF task of rapid elbow flexion for 20 s with the right arm. Wearable gyroscopes were used to measure forearm and upper-arm motion, and electrocardiography were recorded using leads on the left chest. Using this setup, HR dynamics were measured, including time to peak HR, recovery time, percentage increase in HR during UEF, and percentage decrease in HR during recovery after UEF. Results Fifty-six eligible participants were recruited, including 12 non-frail (age = 76.92 ± 7.32 years), and 40 pre-frail (age = 80.53 ± 8.12 years), and four frail individuals (age = 88.25 ± 4.43 years). Analysis of variance models showed that the percentage increase in HR during UEF and percentage decrease in HR during recovery were both 47% smaller in pre-frail/frail older adults compared to non-frails (p < 0.01, effect size = 0.70 and 0.62 for increase and decrease percentages). Using logistic models with both UEF kinematics and HR parameters as independent variables, frailty was predicted with a sensitivity of 0.82 and specificity of 0.83. Conclusion Current findings showed evidence of strong association between HR dynamics and frailty. It is suggested that combining kinematics and HR data in a multimodal model may provide a promising objective tool for frailty assessment.

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Marom, Gil, Mor Peleg, Rotem Halevi, Moshe Rosenfeld, Ehud Raanani, Ashraf Hamdan et Rami Haj-Ali. « Fluid-Structure Interaction Model of Aortic Valve With Porcine-Specific Collagen Fiber Alignment in the Cusps ». Journal of Biomechanical Engineering 135, n^o 10 (13 septembre 2013). http://dx.doi.org/10.1115/1.4024824.

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Native aortic valve cusps are composed of collagen fibers embedded in their layers. Each valve cusp has its own distinctive fiber alignment with varying orientations and sizes of its fiber bundles. However, prior mechanical behavior models have not been able to account for the valve-specific collagen fiber networks (CFN) or for their differences between the cusps. This study investigates the influence of this asymmetry on the hemodynamics by employing two fully coupled fluid-structure interaction (FSI) models, one with asymmetric-mapped CFN from measurements of porcine valve and the other with simplified-symmetric CFN. The FSI models are based on coupled structural and fluid dynamic solvers. The partitioned solver has nonconformal meshes and the flow is modeled by employing the Eulerian approach. The collagen in the CFNs, the surrounding elastin matrix, and the aortic sinus tissues have hyperelastic mechanical behavior. The coaptation is modeled with a master-slave contact algorithm. A full cardiac cycle is simulated by imposing the same physiological blood pressure at the upstream and downstream boundaries for both models. The mapped case showed highly asymmetric valve kinematics and hemodynamics even though there were only small differences between the opening areas and cardiac outputs of the two cases. The regions with a less dense fiber network are more prone to damage since they are subjected to higher principal stress in the tissues and a higher level of flow shear stress. This asymmetric flow leeward of the valve might damage not only the valve itself but also the ascending aorta.

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