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1
Scharf, S. M., L. M. Graver, S. Khilnani, and K. Balaban. "Respiratory phasic effects of inspiratory loading on left ventricular hemodynamics in vagotomized dogs." Journal of Applied Physiology 73, no. 3 (September 1, 1992): 995–1003. http://dx.doi.org/10.1152/jappl.1992.73.3.995.
Повний текст джерелаАнотація:
Exaggerated inspiratory swings in intrathoracic pressure have been postulated to increase left ventricular (LV) afterload. These predictions are based on measurements of LV afterload by use of esophageal or lateral pleural pressure. Using direct measurements of pericardial pressure, we reexamined respiratory changes in LV afterload. In 11 anesthetized vagotomized dogs, we measured arterial pressure, LV end-systolic (ES) and end-diastolic transmural (TM) pressures, stroke volume (SV), diastolic left anterior descending blood flow (CBF-D), and coronary resistance. Dogs were studied before and while breathing against an inspiratory threshold load of -20 to -25 cmH2O compared with end expiration. Relative to end expiration, SV and LVES TM pressures decreased during inspiration and increased during early expiration, effects exaggerated during inspiratory loading. In all cases, LV afterload (LVES TM pressure) changed in parallel with SV. LV end-diastolic TM pressure did not change. CBF-D paralleled arterial pressure, and there were no changes in coronary resistance. In two dogs, regional LVES segment length paralleled calculated changes in LVES TM pressure. We conclude that 1) LV afterload decreases during early inspiration and increases during early expiration, changes secondary to those in SV; 2) changes in CBF-D are secondary to changes in perfusion pressure during the respiratory cycle; and 3) the use of esophageal or lateral pleural pressure to estimate LV surface pressure overestimates changes in LV TM pressures during respiration.
2
Vercellin, Alice Verticchio, Alon Harris, Brent Siesky, Ryan Zukerman, Lucia Tanga, Carmela Carnevale, Fabio Scarinci, and Francesco Oddone. "Agreement of rebound and applanation tonometry intraocular pressure measurements during atmospheric pressure change." PLOS ONE 16, no. 10 (October 28, 2021): e0259143. http://dx.doi.org/10.1371/journal.pone.0259143.
Повний текст джерелаАнотація:
This study investigated the agreement of intraocular pressure measurements using rebound tonometry and applanation tonometry in response to atmospheric changes in a hyperbaric chamber. Twelve eyes of 12 healthy subjects were included in this prospective, comparative, single-masked study. Intraocular pressure measurements were performed by rebound tonometry followed by applanation tonometry in a multiplace hyperbaric chamber at 1 Bar, followed by 2, 3 and 4 Bar during compression and again at 3 and 2 Bar during decompression. Mean differences between rebound and applanation intraocular pressure measurements were 1.6, 1.7, and 2.1 mmHg at 2, 3, and 4 Bar respectively during compression and 2.6 and 2.2 mmHg at 3 and 2 Bar during decompression. Lower limits of agreement ranged from -3.7 to -5.9 mmHg and upper limits ranged from -0.3 to 1.9 mmHg. Multivariate analysis showed that the differences between rebound and applanation intraocular pressure measurements were independent of atmospheric pressure changes (p = 0.79). Intraocular pressure measured by rebound tonometry shows a systematic difference compared to intraocular measured by applanation tonometry, but this difference is not influenced by changes of atmospheric pressure up to 4 Bar in a hyperbaric chamber. Agreement in magnitude of change between devices suggests rebound tonometry is viable for assessing intraocular pressure during atmospheric changes. Future studies should be designed in consideration of expected differences in IOP values provided by the two devices.
3
Maass-Moreno, R., and C. F. Rothe. "Nonlinear resistances in hepatic microcirculation." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 6 (December 1, 1995): H1922—H1930. http://dx.doi.org/10.1152/ajpheart.1995.269.6.h1922.
Повний текст джерелаАнотація:
The liver provides a reservoir available for mobilizing large amounts of blood, but if a change in downstream (outflow) pressure below a certain magnitude (break pressure) does not change upstream pressures, blood volume redistribution may be limited. For downstream pressures larger than the break pressure, the upstream pressures change proportionately. We tested the hypothesis that this nonlinear mode of pressure transmission could be found from the abdominal vena cava to the hepatic microcirculation and from the hepatic microcirculation to the portal vein. Using a servo-null micropipette technique, we measured microvascular pressures at the liver surface of rabbits. In 16 of 30 measurements, increasing the pressure at the liver outflow, by partially occluding the caudal thoracic vena cava, caused an increase in hepatic venular pressure only after the abdominal vena caval pressure exceeded a break pressure of 2.85 +/- 0.92 mmHg. In 13 of 31 measurements, portal venous pressure was not changed until the hepatic venular pressure exceeded a break pressure of 3.36 +/- 0.54 mmHg. Similar behavior and values were obtained for sinusoids and portal venules. When present, the sharp inflection in the upstream-downstream pressure plots suggests that this may be caused by a Starling resistor-type mechanism. When the break was absent, the downstream pressure may have been larger than the break pressure. We conclude that significant hepatic resistances with nonlinear characteristics exist upstream and downstream to the central venules, sinusoids, and portal venules.
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Reischl, Uwe, and Conrad Colby. "Simplifying Blood Pressure Measurements in Clinical Settings." International Journal Of Community Medicine And Public Health 10, no. 1 (December 29, 2022): 52. http://dx.doi.org/10.18203/2394-6040.ijcmph20223525.
Повний текст джерелаАнотація:
Background: Upper arm sphygmomanometry is the most commonly used method to measure blood pressure in adults. However, variations in upper arm circumference and use of different cuff-sizes results in different pressure readings. When using the same cuff size, pressure readings will be higher for larger arm circumferences and lower for smaller arm circumferences. The objective of this study was to identify an adjustment factor that will allow pressure readings obtained for any combination of arm circumference and cuff size to be compared.Methods: To investigate the relationship between arm circumferences, cuff size and pressure readings, experiments were conducted using laboratory simulations and blood pressure measurements on nineteen human subjects. Power analysis identified minimum sample size. Results were analyzed using Chi-square and t-tests. The study was conducted between 2019 and 2021 in Boise, Idaho, USA. The University institutional review board approved the use of human subjects.Results: Simulations revealed a 99% linear correlation between changes in arm circumference coverage and changes in pressure readings. Human subject tests showed a 1% change in upper arm coverage by the sphygmomanometer cuff corresponded to a 1mmHg change in both systolic and diastolic pressure readings. Conclusions: The proposed adjustment factor can simplify blood pressure measurements in clinical settings by allowing healthcare providers to use only one sphygmomanometer size. It will also provide the basis for a “reference” against which blood pressure values obtained for any combination of cuff size and arm circumference can be standardized.
5
Rome, Keith, David George Survepalli, Maria Lobo, Nicola Dalbeth, Fiona McQueen, and Peter J. McNair. "Evaluating Intratester Reliability of Manual Masking of Plantar Pressure Measurements Associated with Chronic Gout." Journal of the American Podiatric Medical Association 101, no. 5 (September 1, 2011): 424–29. http://dx.doi.org/10.7547/1010424.
Повний текст джерелаАнотація:
Background: Plantar pressure measurements are commonly used to evaluate foot function in chronic musculoskeletal conditions. However, manually identifying anatomical landmarks is a source of measurement error and can produce unreliable data. The aim of this study was to evaluate intratester reliability associated with manual masking of plantar pressure measurements in patients with gout. Methods: Twenty-five patients with chronic gout (mean disease duration, 22 years) were recruited from rheumatology outpatient clinics. Patients were excluded if they were experiencing an acute gout flare at the time of assessment, had lower-limb amputation, or had diabetes mellitus. Manual masking of peak plantar pressures and pressure-time integrals under ten regions of the foot were undertaken on two occasions on the same day using an in-shoe pressure measurement system. Test-retest reliability was assessed by using intraclass correlation coefficients, SEM, 95% limits of agreement, and minimal detectable change. Results: Mean peak pressure intraclass correlation coefficients ranged from 0.92 to 0.97, with SEM of 8% to 14%. The 95% limits of agreement ranged from−150.3 to 133.5 kPa, and the minimal detectable change ranged from 30.8 to 80.6 kPa. For pressure-time integrals, intraclass correlation coefficients were 0.86 to 0.94, and SEM were 5% to 29%, with the greater errors observed under the toes. The 95% limits of agreement ranged from −48.5 to 48.8 kPa/sec, and the minimal detectable change ranged from 6.8 to 21.0 kPa/sec. Conclusions: These findings provide clinicians with information confirming the errors associated with manual masking of plantar pressure measurements in patients with gout. (J Am Podiatr Med Assoc 101(5): 424–429, 2011)
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Sandmann, M., and A. Würflinger. "PVT Measurements on 4′-n-Octyl-Biphenyl-4-Carbonitrile (8CB) up to 300 MPa." Zeitschrift für Naturforschung A 53, no. 9 (September 1, 1998): 787–92. http://dx.doi.org/10.1515/zna-1998-0910.
Повний текст джерелаАнотація:
Abstract P, Vm , Tdata have been measured for the smectic, nematic and isotropic phases of 4'-n-octyl-biphen-yl-4-carbonitrile (8CB) in the temperature range 300-370 K and pressures up to 300 MPa. At atmospheric pressure all phase transitions appear to be of first order due to a discontinuity in the density. The volume change at the smectic A -nematic transition is only a tenth of the volume change at the clearing temperature. At moderate pressures below 80 MPa the SA -N transition could be detected as a discontinuity in the period of oscillation in measurements with a high-pressure vibrating tube densimeter. At higher pressures the discontinuity seems to die away, possibly indicating a change from first order to second order transition. From the volume changes and the slopes of the transition lines we calculate the enthalpy changes at the phase transition. The p, Vm , T data enable us to calculate the volume part of the entropy and the molecular field parameter γ=δln TNI/δln VNI .
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Szczucka-Lasota, Bożena, Tomasz Węgrzyn, Maciej kAZANOWSKI, and Łukasz Wszołek. "Influence of selected parameters on the quality of technical tests braking system." Scientific Papers of Silesian University of Technology. Organization and Management Series 2022, no. 158 (2022): 589–98. http://dx.doi.org/10.29119/1641-3466.2022.158.38.
Повний текст джерелаАнотація:
Purpose: The aim of the study is to find out whether and to extent the change of selected parameters of the system, such as the type of tires, tire pressure and axle load, changes the result of the technical test of the analysed vehicle in the field of measuring braking forces. Design/methodology/approach: Diagnostic tests, tire pressure measurements, axle load measurements, braking force measurements on a roller device were carried out. Findings: The relationships between the pressure in the tires and the braking force measured on the wheel as well as between the braking force and the load acting on the vehicle axle have been demonstrated. Research limitations/implications: Mathematical relationships between tire pressure and vehicle braking force can be derived in the future. Practical implications: In the course of the tests, it was found that the technical tests made it possible to determine the braking forces only while maintaining the nominal ±1×105 Pa tire pressure. Changes to this parameter may influence the measurement results. Moreover, the influence of tire pressure on the change of the measured braking force values was found, which translates into the safety of the vehicle in road traffic. Originality/value: approach to brake system.
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Frigy, Attila, Annamária Magdás, Victor-Dan Moga, Ioana Georgiana Coteț, Miklós Kozlovszky, and László Szilágyi. "Increase of Short-Term Heart Rate Variability Induced by Blood Pressure Measurements during Ambulatory Blood Pressure Monitoring." Computational and Mathematical Methods in Medicine 2017 (2017): 1–5. http://dx.doi.org/10.1155/2017/5235319.
Повний текст джерелаАнотація:
Objective.The possible effect of blood pressure measurements per se on heart rate variability (HRV) was studied in the setting of concomitant ambulatory blood pressure monitoring (ABPM) and Holter ECG monitoring (HM).Methods.In 25 hypertensive patients (14 women and 11 men, mean age: 58.1 years), 24-hour combined ABPM and HM were performed. For every blood pressure measurement, 2-minute ECG segments (before, during, and after measurement) were analyzed to obtain time domain parameters of HRV: SDNN and rMSSD. Mean of normal RR intervals (MNN), SDNN/MNN, and rMSSD/MNN were calculated, too. Parameter variations related to blood pressure measurements were analyzed using one-way ANOVA with multiple comparisons.Results.2281 measurements (1518 during the day and 763 during the night) were included in the analysis. Both SDNN and SDNN/MNN had a constant (the same for 24-hour, daytime, and nighttime values) and significant change related to blood pressure measurements: an increase during measurements and a decrease after them (p<0.01for any variation).Conclusion.In the setting of combined ABPM and HM, the blood pressure measurement itself produces an increase in short-term heart rate variability. Clarifying the physiological basis and the possible clinical value of this phenomenon needs further studies.
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Huhle, Robert, Thorsten Richter, and Marcelo Gama de Abreu. "Tracking blood pressure changes by means of non-invasive intermittent blood pressure measurements in clinical application." Current Directions in Biomedical Engineering 7, no. 2 (October 1, 2021): 815–18. http://dx.doi.org/10.1515/cdbme-2021-2208.
Повний текст джерелаАнотація:
Abstract Considering accuracy/precision cut-offs of 5 ± 8 mmHg and cut-off values for inter-class correlation coefficients (ICC=0.37...1, from DIN EN ISO 81060-2), absolute and relative errors in time independent measurement of blood pressure changes with non-invasive intermittent devices (NiBP) are derived mathematically for mean arterial blood pressure range of 40-180 mmHg. As a clinically relevant value for change of arterial blood pressure 20% of the baseline blood pressure is considered. The mean ratio between the change of BP measured by the NiBP and measured by the invasive reference device (TE%) were proposed as quality measure for the evaluation of NiBP device tracking capability. The proposed measure TE%is theoretically independent of absolute accuracy but depends on precision and ICC of a device. NiBP devices show considerable maximum TE% of 41% in tracking mean blood pressure changes respectively. In 10% of the measurements in the low blood pressure range TE% exceeding 100%. The mean 50th/90th TE% percentile over the whole blood pressure range were 25/61%, respectively. Furthermore, TE% was relatively insensitive to assumed blood pressure range but sensitive to ICC. NiBP devices have high relative error in tracking blood pressure changes that make those devices not well-suited for tracking blood pressure changes. The proposed tracking error allows the definition of reasonable accuracy/precision requirements of NBP devices.
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Hughes, Chris W., Shane Elipot, Miguel Ángel Morales Maqueda, and John W. Loder. "Test of a Method for Monitoring the Geostrophic Meridional Overturning Circulation Using Only Boundary Measurements." Journal of Atmospheric and Oceanic Technology 30, no. 4 (April 1, 2013): 789–809. http://dx.doi.org/10.1175/jtech-d-12-00149.1.
Повний текст джерелаАнотація:
Abstract Measurements of ocean bottom pressure, particularly on the continental slope, make an efficient means of monitoring large-scale integrals of the ocean circulation. However, direct pressure measurements are limited to monitoring relatively short time scales (compared to the deployment period) because of problems with sensor drift. Measurements are used from the northwest Atlantic continental slope, as part of the Rapid Climate Change (RAPID)–West Atlantic Variability Experiment, to demonstrate that the drift problem can be overcome by using near-boundary measurements of density and velocity to reconstruct bottom pressure differences with accuracy better than 1 cm of water (100 Pa). This accuracy permits the measurement of changes in the zonally integrated flow, below and relative to 1100 m, to an accuracy of 1 Sv (1 Sv ≡ 106 m3 s−1) or better. The technique employs the “stepping method,” a generalization of hydrostatic balance for sloping paths that uses geostrophic current measurements to reconstruct the horizontal component of the pressure gradient.
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Prasad, Manika. "Acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection." GEOPHYSICS 67, no. 2 (March 2002): 405–12. http://dx.doi.org/10.1190/1.1468600.
Повний текст джерелаАнотація:
Shallow water flows and over‐pressured zones are a major hazard in deepwater drilling projects. Their detection prior to drilling would save millions of dollars in lost drilling costs. I have investigated the sensitivity of seismic methods for this purpose. Using P‐wave information alone can be ambiguous, because a drop in P‐wave velocity (Vp) can be caused both by overpressure and by presence of gas. The ratio of P‐wave velocity to S‐wave velocity (Vp/Vs), which increases with overpressure and decreases with gas saturation, can help differentiate between the two cases. Since P‐wave velocity in a suspension is slightly below that of the suspending fluid and Vs=0, Vp/Vs and Poisson's ratio must increase exponentially as a load‐bearing sediment approaches a state of suspension. On the other hand, presence of gas will also decrease Vp but Vs will remain unaffected and Vp/Vs will decrease. Analyses of ultrasonic P‐ and S‐wave velocities in sands show that the Vp/Vs ratio, especially at low effective pressures, decreases rapidly with pressure. At very low pressures, Vp/Vs values can be as large as 100 and higher. Above pressures greater than 2 MPa, it plateaus and does not change much with pressure. There is significant change in signal amplitudes and frequency of shear waves below 1 MPa. The current ultrasonic data shows that Vp/Vs values can be invaluable indicators of low differential pressures.
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Owens, Robert L., Atul Malhotra, Danny J. Eckert, David P. White, and Amy S. Jordan. "The influence of end-expiratory lung volume on measurements of pharyngeal collapsibility." Journal of Applied Physiology 108, no. 2 (February 2010): 445–51. http://dx.doi.org/10.1152/japplphysiol.00755.2009.
Повний текст джерелаАнотація:
Changes in end-expiratory lung volume (EELV) affect upper airway stability. The passive pharyngeal critical pressure (Pcrit), a measure of upper airway collapsibility, is determined using airway pressure drops. The EELV change during these drops has not been quantified and may differ between obese obstructive sleep apnea (OSA) patients and controls. Continuous positive airway pressure (CPAP)-treated OSA patients and controls were instrumented with an epiglottic catheter, magnetometers (to measure change in EELV), and a nasal mask/pneumotachograph. Subjects slept supine in a head-out plastic chamber in which the extrathoracic pressure could be lowered (to raise EELV) while on nasal CPAP. The magnitude of EELV change during Pcrit measurement (sudden reductions of CPAP for 3–5 breaths each minute) was assessed at baseline and with EELV increased ∼500 ml. Fifteen OSA patients and 7 controls were studied. EELV change during Pcrit measurement was rapid and pressure dependent, but similar in OSA and control subjects (74 ± 36 and 59 ± 24 ml/cmH2O respectively, P = 0.33). Increased lung volume (mean +521 ml) decreased Pcrit by a similar amount in OSA and control subjects (−3.1 ± 1.7 vs. −3.9 ± 1.9 cmH2O, P = 0.31). Important lung volume changes occur during passive Pcrit measurement. However, on average, there is no difference in lung volume change for a given CPAP change between obese OSA subjects and controls. Changes in lung volume alter Pcrit substantially. This work supports a role for lung volume in the pathogenesis of OSA, and lung volume changes should be a consideration during assessment of pharyngeal mechanics.
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Baker, Jason, Ravhi Kumar, Changyong Park, Curtis Kenney-Benson, Andrew Cornelius, and Nenad Velisavljevic. "High-pressure Seebeck coefficients and thermoelectric behaviors of Bi and PbTe measured using a Paris-Edinburgh cell." Journal of Synchrotron Radiation 23, no. 6 (October 17, 2016): 1368–78. http://dx.doi.org/10.1107/s1600577516014521.
Повний текст джерелаАнотація:
A new sample cell assembly design for the Paris-Edinburgh type large-volume press for simultaneous measurements of X-ray diffraction, electrical resistance, Seebeck coefficient and relative changes in the thermal conductance at high pressures has been developed. The feasibility of performingin situmeasurements of the Seebeck coefficient and thermal measurements is demonstrated by observing well known solid–solid phase transitions of bismuth (Bi) up to 3 GPa and 450 K. A reversible polarity flip has been observed in the Seebeck coefficient across the Bi-I to Bi-II phase boundary. Also, successful Seebeck coefficient measurements have been performed for the classical high-temperature thermoelectric material PbTe under high pressure and temperature conditions. In addition, the relative change in the thermal conductivity was measured and a relative change in ZT, the dimensionless figure of merit, is described. This new capability enables pressure-induced structural changes to be directly correlated to electrical and thermal properties.
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Bunnell, Avianne, and Michael L. Cheatham. "Airway Pressures as Surrogate Estimates of Intra-abdominal Pressure." American Surgeon 81, no. 1 (January 2015): 81–85. http://dx.doi.org/10.1177/000313481508100134.
Повний текст джерелаАнотація:
Intra-abdominal pressure (IAP) measurements are essential to the diagnosis and management of patients with intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS). Peak inspiratory pressure (PIP), plateau pressure (Pplat), and mean airway pressure (Paw) are used by some surgeons as surrogate estimates of IAP during abdominal closure. Thirty mechanically ventilated surgical/trauma patients with risk factors for IAH/ACS underwent simultaneous triplicate measurements of PIP, Pplat, Paw, and IAP. PIP, Pplat, and Paw were compared with IAP using both coefficient of determination and Bland and Altman analysis. The coefficient of determination for each airway pressure in predicting change in IAP was: PIP 5 per cent ( P = 0.24), Pplat 17 per cent ( P = 0.02), and Paw 15 per cent ( P = 0.03). Bland and Altman analysis identified that marked variability exists between airway pressure and IAP measurements: PIP 19.3 ± 18.7 mmHg, Pplat 11.1 ± 13.7 mmHg, and Paw 2.0 ± 9.8 mmHg. Airway pressures do not accurately reflect IAP and cannot be substituted for IAP measurements in patients at risk for IAH/ACS.
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Finkelstein, Yehuda, Yuval Zohar, Yoav P. Talmi, and Nelu Laurian. "Study of Toynbee Phenomenon by Combined Intranasopharyngeal and Tympanometric Measurements." Annals of Otology, Rhinology & Laryngology 97, no. 2 (March 1988): 199–206. http://dx.doi.org/10.1177/000348948809700220.
Повний текст джерелаАнотація:
The Toynbee maneuver, swallowing when the nose is obstructed, leads in most cases to pressure changes in one or both middle ears, resulting in a sensation of fullness. Since first described, many varying and contradictory comments have been reported in the literature concerning the type and amount of pressure changes both in the nasopharynx and in the middle ear. In our study, the pressure changes were determined by catheters placed into the nasopharynx and repeated tympanometric measurements. New information concerning the rapid pressure variations in the nasopharynx and middle ear during deglutition with an obstructed nose was obtained. Typical individual nasopharyngeal pressure change patterns were recorded, ranging from a maximal positive pressure of + 450 to a negative pressure as low as −320 mm H2O.
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Glucksberg, M. R., and J. Bhattacharya. "Effect of alveolar and pleural pressures on interstitial pressures in isolated dog lungs." Journal of Applied Physiology 70, no. 2 (February 1, 1991): 914–18. http://dx.doi.org/10.1152/jappl.1991.70.2.914.
Повний текст джерелаАнотація:
We report the first direct measurements of perialveolar interstitial pressures in lungs inflated with negative pleural pressure. In eight experiments, we varied surrounding (pleural) pressure in a dog lung lobe to maintain constant inflation with either positive alveolar and ambient atmospheric pleural pressures (positive inflation) or ambient atmospheric alveolar and negative pleural pressures (negative inflation). Throughout, vascular pressure was approximately 4 cmH2O above pleural pressure. By the micropuncture servo-null technique we recorded interstitial pressures at alveolar junctions (Pjct) and in the perimicrovascular adventitia (Padv). At transpulmonary pressure of 7 cmH2O (n = 4), the difference of Pjct and Pady from pleural pressure of 0.9 +/- 0.4 and -1.1 +/- 0.2 cmH2O, respectively, during positive inflation did not significantly change (P less than 0.05) after negative inflation. After increase of transpulmonary pressure from 7 to 15 cmH2O (n = 4), the decrease of Pjct by 3.3 +/- 0.3 cmH2O and Pady by 2.0 +/- 0.4 cmH2O during positive inflation did not change during negative inflation. The Pjct-Pady gradient was not affected by the mode of inflation. Our measurements indicate that, in lung, when all pressures are referred to pleural or alveolar pressure, the mode of inflation does not affect perialveolar interstitial pressures.
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Biro, George P. "Large venous compliance in carboxyhemoglobinemia and hemodilutional anemia." Canadian Journal of Physiology and Pharmacology 64, no. 5 (May 1, 1986): 556–60. http://dx.doi.org/10.1139/y86-092.
Повний текст джерелаАнотація:
Anesthetized dogs were prepared for the measurement of compliance of the inferior vena cava by placement of a catheter for pressure measurement and a pair of ultrasonic dimension transducers for the measurement of transverse diameter. Measurements of compliance were made in a control state, after the induction of carboxyhemoglobinemia or hemodilutional anemia, by measuring pressure changes and diameter changes during brief occlusions of the inferior vena cava downstream from the transducers. Carboxyhemoglobinemia cuased an upward shift of the averaged pressure–diameter curve while there was a negligible shift in the hemodiluted group. These results indicate that in carboxyhemoglobinemia a change in the compliance of the vena cava occurs, which favours augmented venous return by improved conductance rather than by a dislocation of blood by constriction of the large venous reservoir. In hemodilutional anemia the change in compliance is insignificant, but venous return is favoured by the reduced viscosity.
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Bandiello, Enrico, Josu Sánchez-Martín, Daniel Errandonea, and Marco Bettinelli. "Pressure Effects on the Optical Properties of NdVO4." Crystals 9, no. 5 (May 6, 2019): 237. http://dx.doi.org/10.3390/cryst9050237.
Повний текст джерелаАнотація:
We report on optical spectroscopic measurements in pure NdVO4 crystals at pressures up to 12 GPa. The influence of pressure on the fundamental absorption band gap and Nd3+ absorption bands has been correlated with structural changes in the crystal. The experiments indicate that a phase transition takes place between 4.7 and 5.4 GPa. We have also determined the pressure dependence of the band-gap and discussed the behavior of the Nd3+ absorption lines under compression. Important changes in the optical properties of NdVO4 occur at the phase transition, which, according to Raman measurements, corresponds to a zircon to monazite phase change. In particular, in these conditions a collapse of the band gap occurs, changing the color of the crystal. The changes are not reversible. The results are analyzed in comparison with those deriving from previous studies on NdVO4 and related vanadates.
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Iyengar, Jennifer J., Matthew Johnson, Shafaq Khairi, Jessica E. Fennelly, and Jennifer Wyckoff. "Improving the quality of blood pressure measurements in an outpatient diabetes clinic." BMJ Open Quality 10, no. 1 (January 2021): e000917. http://dx.doi.org/10.1136/bmjoq-2020-000917.
Повний текст джерелаАнотація:
Hypertension is an important modifiable risk factor for cardiovascular disease in patients with diabetes. Despite established guidelines, the percentage of patients meeting the target blood pressure (BP) of <140/90 mm Hg in clinic remains suboptimal. In this project, we sought to improve BP measurement in an outpatient diabetes clinic.Two interventions were performed: (1) Changes were made to the timing of BP measurement during patient intake and (2) An electronic medical record (EMR) alert reminded staff to repeat BP if the initial reading was above target. Baseline data were collected on 4764 patients, with 72.5% meeting their BP target. After implementation of changes to the timing of BP measurement during patient intake, 73.3% of patients met the target (no significant change). However, after implementation of the EMR alert, there was a statistically significant improvement in patients meeting the target BP at 76.8% (p<0.01). This reduction was driven by the high percentage of patients with an initially elevated BP measurement that came down into goal range on repeat measurement. Those who remained above target despite multiple readings could be referred to a new pharmacist-led hypertension clinic to ensure adequate follow-up and medication adjustment.It is important to ensure that in clinic BP measurements are taken correctly and adhere to best practices. Use of a single in-clinic BP measurement may result in overtreatment of hypertension. While timing of BP measurement during patient intake was not important, repeating high BP measurements did improve the number of patients in an outpatient diabetes clinic meeting their BP target.
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Shuai, Fangsheng, and D. G. Fredlund. "Model for the simulation of swelling-pressure measurements on expansive soils." Canadian Geotechnical Journal 35, no. 1 (February 1, 1998): 96–114. http://dx.doi.org/10.1139/t97-071.
Повний текст джерелаАнотація:
Numerous laboratory swelling tests have been reported for the measurement of swelling pressure and the amount of swell of an expansive soil. These test methods generally involve the use of a conventional one-dimensional oedometer apparatus. Few attempts, however, have been made to formulate a theoretical framework to simulate the testing procedures or to visualize the different stress paths followed when using the various methods. The simulation of the oedometer tests on expansive soils is required to fully understand the prediction of heave. The correct measurement of swelling pressure is required for an accurate prediction of heave. It is further anticipated that some information on unsaturated soils property functions may be approximated from the back-analysis of the data. A theoretical model is proposed to describe the pore-water pressures with time and depth in a specimen as well as the volume changes during various oedometer swell tests. The model is formulated based on equilibrium considerations, constitutive equations for an unsaturated soil, and the continuity requirement for the pore fluid phases. The transient water flow process is coupled with the soil volume change process. The model can be used to describe the volume-change behaviour, pore-water pressure, and vertical total stress development in an unsaturated soil during an oedometer test performed by any one of several test procedures. The model has been put into a finite element formulation using the Galerkin technique. All the parameters required to run the model can be obtained by performing independent, common laboratory tests. The proposed model was used to simulate the results from free-swell, constant-volume, constant water content, and loaded-swell oedometer tests. Computed values of volume change, vertical total stress, and pore-water pressure are in good agreement with measured values.Key words: unsaturated soil, expansive soil, swelling pressure, theoretical simulation, constant-volume oedometer test, free-swell oedometer test, loaded-swell oedometer test.
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Milner, Ross, Hence J. M. Verhagen, Monique Prinssen, and Jan D. Blankensteijn. "Noninvasive Intrasac Pressure Measurement and the Influence of Type 2 and Type 3 Endoleaks in an Animal Model of Abdominal Aortic Aneurysm." Vascular 12, no. 2 (March 2, 2004): 99–105. http://dx.doi.org/10.1258/rsmvasc.12.2.99.
Повний текст джерелаАнотація:
The objective of this study was to noninvasively detect pressure changes within an excluded aneurysm sac in an animal model of abdominal aortic aneurysm (AAA) and to study the influence of type 2 and 3 endoleaks. A porcine model of AAA that allows for the creation of type 2 and 3 endoleaks was used. A miniaturized pressure monitoring device (3 X 9 X 1.5 mm; Remon Medical Technologies, Caesarea, Israel) was implanted within the surgically created and excluded aneurysm sac. The pressure monitoring device is an ultrasound-based system that allows for pressure measurements in a noninvasive, transcutaneous fashion. In addition, catheter-based pressures were taken within the aorta and directly in the AAA sac. Noninvasive measurements were taken in a transcutaneous fashion between the initial operation and the time of sacrifice, when the type 3 endoleak was created (2 weeks). The median mean arterial pressure was 66 mm Hg (range 55–120 mm Hg; N = 8). The median noninvasive sac pressure with a type 2 endoleak was 48 mm Hg (range 39–90 mm Hg; N = 8) and was almost identical to the catheter-based measurements. Noninvasive pressures could be measured as early as postprocedure day 1. Two animals had follow-up that suggested closure of the type 2 endoleak during the observation period. With the creation of the type 3 endoleak, the catheter and noninvasive sac pressure and waveform changed from a flatline trace to a higher-pressure pulsatile trace (median 54 mm Hg; range 46–81 mm Hg; N = 8), reproducing the arterial pressure and waveform. This is the first study, to our knowledge, that demonstrates the efficacy of a noninvasive, miniaturized pressure monitoring device in identifying pressure changes in an excluded aneurysm sac with type 2 and type 3 endoleaks. This technology holds great promise for follow-up of patients and identification of sac pressure changes after EVAR and may allow a change in the current follow-up strategy.
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Riswanto, Riswanto, and Sodikin Sodikin. "Pengukuran Tekanan Absolut Biogas Berbahan Campuran Eceng Gondok Dan Kotoran Sapi." Jurnal Pendidikan Fisika dan Teknologi 5, no. 1 (March 6, 2019): 25. http://dx.doi.org/10.29303/jpft.v5i1.988.
Повний текст джерелаАнотація:
Biogas techniques is a way to produce energy with the anaerobic process by utilizing organic ingredients, one of which can be derived from herbs. The quality of biogas production can be viewed by performing the measurement of absolute pressure of biogas. Absolute pressure is the atmospheric pressure coupled with the measured pressure. The magnitude of the pressure will affect the quality of the flame produced biogas. This study, using the method of observation, and measurements. As for the data analysis techniques,. The findings focused to find the different of biogas production by measuring the change in absolute pressure of biogas. Measurements are done using a manometer. The results obtained show that the introduction by using cow dung retrieved changes pressure biogas occurred on day 3 with pressure 140.565 N/m2, the characteristics of the data graph illustrates the R2 = 0.677. Different results are indicated on the mixing water hyacinth with cow manure, biogas pressure changes happen on day 1 with the characteristic graph of a R2 = 0.976. This condition describes that the mixing of the water hyacinth and cow dung provides distinctions signifikant in accelerating the process of occurrence of biogas.
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Judd, R. M., J. R. Resar, and F. C. Yin. "Rapid measurements of diastolic intramyocardial vascular volume." American Journal of Physiology-Heart and Circulatory Physiology 265, no. 4 (October 1, 1993): H1038—H1047. http://dx.doi.org/10.1152/ajpheart.1993.265.4.h1038.
Повний текст джерелаАнотація:
Rapid measurements of coronary vascular volume are necessary for a complete understanding of phasic coronary flow. Because no standard method is capable of making these measurements, we developed a method that uses digital subtraction angiography to image an intravascular contrast agent. The method is capable of measuring vascular volume in 33 ms and can be repeated three times per second. The method was first validated in phantoms. We then used this method to measure coronary vascular volume in the isolated, perfluorochemical-perfused, interventricular canine septum. The speed of the measurements allowed us, for the first time, to directly measure transients in vascular volume following sudden changes in perfusion pressure. At the steady-state and maximal vasodilation, coronary vascular volume varied from 7.5 +/- 1.2 (SE) ml/100 g at a perfusion pressure of 20 mmHg to 12.1 +/- 1.9 ml/100 g at 90 mmHg, which is similar to other reports. After a sudden change of 40 mmHg in perfusion pressure, vascular volume changed with a time constant of 3.2 +/- 0.3 (SE) s. Increasing ventricular wall stretch had no effect on either the steady-state volumes (P = 0.25) or the time constant for volume changes (P = 0.17). The fact that the time constant is longer than the cardiac cycle, yet much shorter than the time necessary to measure vascular volume using other methods, highlights the need for rapid measurements of vascular volume.
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Muizelaar, J. Paul, John D. Ward, Anthony Marmarou, Pauline G. Newlon, and Akihiko Wachi. "Cerebral blood flow and metabolism in severely head-injured children." Journal of Neurosurgery 71, no. 1 (July 1989): 72–76. http://dx.doi.org/10.3171/jns.1989.71.1.0072.
Повний текст джерелаАнотація:
✓ Autoregulation of cerebral blood flow (“CBF15”) was tested in a series of 26 pediatric patients (mean age 13.2 years) with severe head injury (average Glasgow Coma Scale (GCS) score 5.5) in the acute stage. A baseline 133Xe CBF measurement was performed and then repeated, after blood pressure was increased by 29% with intravenous phenylephrine or decreased by 26% with intravenous trimethaphan camsylate. Correlations were made between CBF and clinical condition, outcome, time after injury, intracranial pressure (ICP), and pressure-volume index (PVI) changes, and the site of injury (hemispheres, diencephalon, or brain stem). The site of injury was determined with multimodality evoked potential measurements. Autoregulation was intact in 22 (59%) of 37 measurements. There was no correlation with GCS score, outcome, time after injury, site of injury, or way of testing (decreasing or increasing blood pressure). Autoregulation was statistically significantly more often impaired when CBF was either below normal −2 standard deviations (SD) (reduced flow) or above normal +2 SD (absolute hyperemia). In cases with intact autoregulation, mean ICP decreased from 17.5 to 15.0 mm Hg with higher blood pressure and increased from 19.0 to 21.3 mm Hg with lower blood pressure. When PVI was measured during the blood pressure manipulations, it was found to change in a direction opposite to the ICP change. The consequences of these findings in the management of ICP problems with blood pressure control are discussed.
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Mailloux, Catherine, Louis-David Beaulieu, Timothy H. Wideman, and Hugo Massé-Alarie. "Within-session test-retest reliability of pressure pain threshold and mechanical temporal summation in healthy subjects." PLOS ONE 16, no. 1 (January 12, 2021): e0245278. http://dx.doi.org/10.1371/journal.pone.0245278.
Повний текст джерелаАнотація:
Objective To determine the absolute and relative intra-rater within-session test-retest reliability of pressure pain threshold (PPT) and mechanical temporal summation of pain (TSP) at the low back and the forearm in healthy participants and to test the influence of the number and sequence of measurements on reliability metrics. Methods In 24 participants, three PPT and TSP measures were assessed at four sites (2 at the low back, 2 at the forearm) in two blocks of measurements separated by 20 minutes. The standard error of measurement, the minimal detectable change (MDC) and the intraclass correlation coefficient (ICC) were investigated for five different sequences of measurements (e.g. measurement 1, 1–2, 1-2-3). Results The MDC for the group (MDCgr) for PPT ranged from 28.71 to 50.56 kPa across the sites tested, whereas MDCgr for TSP varied from 0.33 to 0.57 out of 10 (numeric scale). Almost all ICC showed an excellent relative reliability (between 0.80 and 0.97), except when only the first measurement was considered (moderate). Although minimal differences in absolute PPT reliability were present between the different sequences, in general, using only the first measurement increase measurement error. Three TSP measures reduced the measurement error. Discussion We established that two measurements of PPT and three of TSP reduced the measurement error and demonstrated an excellent relative reliability. Our results could be used in future pain research to confirm the presence of true hypo/hyperalgesia for paradigms such as conditioned pain modulation or exercise-induced hypoalgesia, indicated by a change exceeding the measurement variability.
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Yao, A., C. L. Yang, J. K. Seo, and M. Soleimani. "EIT-Based Fabric Pressure Sensing." Computational and Mathematical Methods in Medicine 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/405325.
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This paper presents EIT-based fabric sensors that aim to provide a pressure mapping using the current carrying and voltage sensing electrodes attached to the boundary of the fabric patch. Pressure-induced shape change over the sensor area makes a change in the conductivity distribution which can be conveyed to the change of boundary current-voltage data. This boundary data is obtained through electrode measurements in EIT system. The corresponding inverse problem is to reconstruct the pressure and deformation map from the relationship between the applied current and the measured voltage on the fabric boundary. Taking advantage of EIT in providing dynamical images of conductivity changes due to pressure induced shape change, the pressure map can be estimated. In this paper, the EIT-based fabric sensor was presented for circular and rectangular sensor geometry. A stretch sensitive fabric was used in circular sensor with 16 electrodes and a pressure sensitive fabric was used in a rectangular sensor with 32 electrodes. A preliminary human test was carried out with the rectangular sensor for foot pressure mapping showing promising results.
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Sato, Takashi, Tomoya Koshi, and Eiji Iwase. "Resistance Change Mechanism of Electronic Component Mounting through Contact Pressure Using Elastic Adhesive." Micromachines 10, no. 6 (June 14, 2019): 396. http://dx.doi.org/10.3390/mi10060396.
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For mounting electronic components through contact pressure using elastic adhesives, a high contact resistance is an inevitable issue in achieving solderless wiring in a low-temperature and low-cost process. To decrease the contact resistance, we investigated the resistance change mechanism by measuring the contact resistance with various contact pressures and copper layer thicknesses. The contact resistivity decreased to 4.2 × 10−8 Ω·m2 as the contact pressure increased to 800 kPa and the copper layer thickness decreased to 5 µm. In addition, we measured the change in the total resistance with various copper layer thicknesses, including the contact and wiring resistance, and obtained the minimum combined resistance of 123 mΩ with a copper-layer thickness of 30 µm using our mounting method. In this measurement, a low contact resistance was obtained with a 5-µm-thick copper layer and a contact pressure of 200 kPa or more; however, there is a trade-off with respect to the copper layer thickness in obtaining the minimum combined resistance because of the increasing wiring resistance. Subsequently, based on these measurements, we developed a sandwich structure to decrease the contact resistance, and a contact resistivity of 8.0 × 10−8 Ω·m2 was obtained with the proposed structure.
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Zarrati, A. R., Yee-Chung Jin, A. Shanehsaz-zadeh, and F. Ahadi. "Potential flow solution for a free surface flow past a sudden slope change." Canadian Journal of Civil Engineering 31, no. 4 (August 1, 2004): 553–60. http://dx.doi.org/10.1139/l04-021.
Повний текст джерелаАнотація:
An analytical model was developed to calculate the pressure distribution in a free surface flow past a sudden change in channel slope. A conformal transformation technique was used to solve the problem analytically in a way that there is no need for trial and error to find the location of the free surface. Two methods were employed for this simulation: flow at a corner and free streamline theory. It was shown that free streamline theory is more accurate. Experiments were conducted to verify the ability of the analytical model to calculate the pressure distribution in a channel with a sudden change in slope. Slope changes of 6.22°, 10°, and 15° were tested with various flow discharges. The analytical model predictions of pressure distribution along the channel bed and with depth agreed well with the experimental measurements. Pressures up to 25 times the hydrostatic pressure were experimentally measured near the point of sudden change in slope. These pressures were reproduced by the model. The analytical model predictions of the water surface profile over a ramp in a prototype spillway were compared with those of a numerical model. The comparison showed a good agreement.Key words: pressure distribution, free surface flow, analytical model, chute spillway, aerator ramp, potential flow.
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Hussein, O., W. Z. Wan Hasan, A. Che Soh, H. Jafaar, H. R. Ramli, S. P. Ang, and Zainidi Haji Abdul Hamid. "In-sole plantar pressure device with optimization measurement techniques." Indonesian Journal of Electrical Engineering and Computer Science 17, no. 2 (February 1, 2020): 739. http://dx.doi.org/10.11591/ijeecs.v17.i2.pp739-749.
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<span style="font-size: 9pt; font-family: 'Times New Roman', serif;" lang="EN-GB">Doctors and clinicians rely on accurate underfoot pressure data to perform diagnosis of foot diseases. In sole pressure measurement systems are designed to provide such data but its implementation suffers from certain constraints such as the need for a spacer to be placed on the sensor when taking measurements and the need for multiple calibrations due to the fact that the sensor parameters tend to change without it. In this work, we proposed an optimization technique to address these limitations. The results obtained from testing indicate that the proposed device performed measurement of plantar pressure effectively. Also, the calculation of body weight using the proposed optimization technique is improved from 5.07% to 9.06%. For validation, the results are compared with the measurements from a commercial plantar pressure device (EMED system) as benchmark. </span>
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Parkinson, S., C. Belleau, J. Homan, and B. Richardson. "Flow and velocity waveform indices in the ovine fetal abdominal aorta with changes in behavioural state." Reproduction, Fertility and Development 7, no. 5 (1995): 1299. http://dx.doi.org/10.1071/rd9951299.
Повний текст джерелаАнотація:
The purpose of this study was to determine the extent to which flow and velocity waveform indices are comparable as measured from the ovine fetal abdominal aorta and reflect downstream vascular resistance with changes in electrocortical activity. Nine chronically catheterized fetal sheep were studied near term with continuous measurement of electrocortical activity, perfusion pressure, and fetal heart rate. A cuffed Doppler crystal and a Transonic flow probe on the descending abdominal aorta were used for the simultaneous measurement of velocity waveforms and flow waveforms, with the Resistance Index (RI), calculated for each. Mean blood flow was also obtained from the Transonic flow probe. Whereas the change in cardiovascular parameters between the low- and high-voltage electrocortical activity (ECOG) states was small, with little relationship to the change in RI measurements, across all animals there was an inverse correlation between the RI measurements and fetal heart rate, perfusion pressure and aortic blood flow during both low- and high-voltage ECOG states. The RI as measured from the velocity waveforms showed only a modest correlation to those measured from the flow waveforms. It is concluded that over the range of circulatory change generated with spontaneous change in behavioural state, the RI as measured in the abdominal aorta of the ovine fetus is primarily determined by pulsatile cardiovascular variables rather than lower body vascular resistance.
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Lee, Seung Yeol, and Hyun Seok. "730 Clinical utility of the portable pressure measuring device for garment therapy on burn scar." Journal of Burn Care & Research 43, Supplement_1 (March 23, 2022): S171. http://dx.doi.org/10.1093/jbcr/irac012.284.
Повний текст джерелаАнотація:
Abstract Introduction The experimenters developed a portable pressure measuring device using silicon piezoresistive pressure sensors. The purpose of this study was to determine the effectiveness of pressure garment therapy using proposed device with objective data obtained through a randomized controlled trial. Methods Pressure measurements were acquired through a readout circuit consisting of an analog-to-digital converter, a microprocessor, and a Bluetooth transmission module for wireless data transmission to an external device. This was a double-blinded, randomized, controlled trial in patients with hypertrophic scars. In the pressure monitoring group, garment pressures were monitored using the portable pressure measuring device, and the compression garment was adjusted so that the pressure was maintained at the therapeutic range of 15 – 25 mmHg. In the control group, non-surgical standard treatment of burn scars except for pressure monitoring was performed in the same manner. Results No significant intergroup difference was noted at the initial evaluations (p >0.05) between two groups. The pre- to post-treatment change in the scar thickness (p=0.03) and erythema (p=0.03), more reductions were found in the pressure monitoring group than control group. There were no significant differences in the change measurements between the two groups for melanin levels (p=0.62) and transepidermal water loss (TEWL) (p=0.94). The changes (skin distensibility, biological skin elasticity, gross skin elasticity, and skin viscoelasticity) measured with the cutometer showed no significant differences between the two groups (p=0.87, p=0.32, p=0.37, and p=0.29, respectively). Conclusions Complementary characteristics such as wireless transmission to an external device may allow burn patients to continuously wear the device for real-time measurements. A Portable pressure monitoring device is effective for significantly improving burn-associated scar characteristics.
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Nomoto, T., T. Maruyama, S. Yamashita, H. Akutsu, and Y. Nakazawa. "Development of frequency tuning AC modulation method for high-pressure heat capacity measurements of molecules-based compounds." Modern Physics Letters B 34, no. 19n20 (July 6, 2020): 2040062. http://dx.doi.org/10.1142/s021798492040062x.
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The automatic frequency tuning method in the high-pressure ac calorimetry system constructed to measure heat capacity for molecules-based compounds with CuBe[Formula: see text]+[Formula: see text]NiCrAl cramp-type pressure cell is reported. This development is performed for increasing resolution and temperature ranges of the heat capacity measurements under external pressure up to 2.0 GPa. The system can check the appropriate conditions by tracing frequency dependence of [Formula: see text] to determine the oscillation frequency at the center of the plateau region of this value. The experiments using the powder samples of metal complexes clarified that the appropriate frequency changes sensitively depending on the difference of temperature and that of external pressures, especially at low temperature region. It decreases with increasing temperature and this relation was found to be almost linear with temperature in ambient pressure and under pressure conditions. The change of thermal diffusion from the sample part to the heat bath should be treated carefully in order to get enough resolution in high pressure AC heat capacity measurements of molecule-based compounds.
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Halleaux, Douglas G., Jeffery M. Sussman, and Nilton O. Rennó. "The Michigan Prandtl System: An Instrument for Accurate Pressure Measurements in Convective Vortices." Journal of Atmospheric and Oceanic Technology 30, no. 10 (October 1, 2013): 2426–33. http://dx.doi.org/10.1175/jtech-d-12-00246.1.
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Abstract This article describes a Prandtl tube system developed at the University of Michigan to measure the static pressure, the total (or stagnation) pressure, and the velocity in flows whose direction and intensity change rapidly. The ever-changing wind vectors in convective vortices are a challenge for making accurate measurements on them. Accurate measurements of the static pressure are particularly problematic because they require the sensor air intake to be aligned perpendicular to the wind direction. This article describes calibrations and tests of the Michigan Prandtl System (MPS) and, in particular, the characterization of the errors in the static pressure measurements as a function of misalignments between the Prandtl tube and the wind vector. This article shows that the MPS measures the pressure with a relative error of 3.5% for wind flows whose direction is within about 10° of the MPS tube direction. It also shows that the MPS adjusts to changes in wind direction of 90° in about 1.5 s, the average rate of change expected in a typical dust devil of about 15 m of radius traveling at 10 m s−1 (Rennó et al.). Field tests indicate that misalignments between the MPS and the wind vector are usually smaller than ~30° during measurements in dust devils and that these misalignments always cause increases in the static pressure measured and decreases in the total pressure measured.
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Burnier, Michel, Sverre E. Kjeldsen, Krzysztof Narkiewicz, and Suzanne Oparil. "Cuff-less measurements of blood pressure: are we ready for a change?" Blood Pressure 30, no. 4 (July 4, 2021): 205–7. http://dx.doi.org/10.1080/08037051.2021.1956178.
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Kawaguchi, Shogo, Michitaka Takemoto, Hideki Tanaka, Shotaro Hiraide, Kunihisa Sugimoto, and Yoshiki Kubota. "Fast continuous measurement of synchrotron powder diffraction synchronized with controlling gas and vapour pressures at beamline BL02B2 of SPring-8." Journal of Synchrotron Radiation 27, no. 3 (March 16, 2020): 616–24. http://dx.doi.org/10.1107/s1600577520001599.
Повний текст джерелаАнотація:
A gas- and vapour-pressure control system synchronized with the continuous data acquisition of millisecond high-resolution powder diffraction measurements was developed to study structural change processes in gas storage and reaction materials such as metal organic framework compounds, zeolite and layered double hydroxide. The apparatus, which can be set up on beamline BL02B2 at SPring-8, mainly comprises a pressure control system of gases and vapour, a gas cell for a capillary sample, and six one-dimensional solid-state (MYTHEN) detectors. The pressure control system can be remotely controlled via developed software connected to a diffraction measurement system and can be operated in the closed gas and vapour line system. By using the temperature-control system on the sample, high-resolution powder diffraction data can be obtained under gas and vapour pressures ranging from 1 Pa to 130 kPa in temperatures ranging from 30 to 1473 K. This system enables one to perform automatic and high-throughput in situ X-ray powder diffraction experiments even at extremely low pressures. Furthermore, this developed system is useful for studying crystal structures during the adsorption/desorption processes, as acquired by millisecond and continuous powder diffraction measurements. The acquisition of diffraction data can be synchronized with the control of the pressure with a high frame rate of up to 100 Hz. In situ and time-resolved powder diffraction measurements are demonstrated for nanoporous Cu coordination polymer in various gas and vapour atmospheres.
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Allison, R. C., B. Rippe, V. R. Prasad, J. C. Parker, and A. E. Taylor. "Pulmonary vascular permeability and resistance measurements in control and ANTU-injured dog lungs." American Journal of Physiology-Heart and Circulatory Physiology 256, no. 6 (June 1, 1989): H1711—H1718. http://dx.doi.org/10.1152/ajpheart.1989.256.6.h1711.
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Because questions have arisen regarding pulmonary vascular permeability and resistance measurements in isolated, perfused lungs, we sought to determine the 1) stability of repeated measurements of permeability and resistance in control lungs; and 2) magnitude of change in these measurements when permeability was greatly increased. Using blood-perfused dog lungs, we measured filtration coefficient (Kf) and isogravimetric capillary pressure (Pci) as indexes of vascular permeability, and we also determined total vascular resistance (Rt) as well as the segmental resistances using the double-occlusion pressure (Pdo). In a control group (n = 8), the base-line measurement of Kf (0.21 +/- 0.02 ml.min-1.cmH2O-1.100 g-1) and Pci (10.2 +/- 0.9 cmH2O) did not change over 4 h, indicating no changes in endothelial barrier function. Base-line Rt (13.9 +/- 2.6 cmH2O.l-1.min.100 g) also did not significantly increase. In a second group (n = 5), alpha-naphthylthiourea (ANTU) increased the initial Kf more than eight times (from 0.17 +/- 0.03 to 1.40 +/- 0.32 ml.min-1.cmH2O-1.100 g-1) and decreased Pci by 56% (from 9.4 +/- 0.6 to 4.1 +/- 0.4 cmH2O) at 1 h, indicating severely damaged endothelium. In addition, the Pdo determined during isogravimetric conditions correlated very well with Pci not only in control lungs (observed previously) but also in very permeable lungs (not previously reported). We conclude that this experimental model provides an excellent means of assessing changes in pulmonary microvascular permeability, with a spectrum ranging from no changes in hourly measurements for 4 h to obvious changes in permeability by 1 h.
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Treiber, Frank A., Francis McCaffrey, William B. Strong, Harry Davis, and Tom Baranowski. "Automated Exercise Blood Pressure Measurements in Children: A Preliminary Study." Pediatric Exercise Science 3, no. 4 (November 1991): 290–99. http://dx.doi.org/10.1123/pes.3.4.290.
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This study compared blood pressure and heart rate measurements provided by the Quinton 410 automated exercise monitor with simultaneous auscultatory and electrocardiograph readings during rest, postural change, immediately after each treadmill exercise workload, and during active recovery in a sample of young children (mean age 7.9 yrs). The Quinton 410 provided highly accurate heart rates under all conditions (average mean difference <1.0 bpm). The Quinton systolic readings correlated well with and were similar to auscultation across conditions except for the initial treadmill workload. Slightly weaker relationships were observed between the Quinton and K4 diastolic comparisons. Compared with K4 auscultatory readings, the Quinton 410 provided slightly lower diastolic pressures across conditions (average mean difference = 3.1 mmHg). These findings provide preliminary evidence that for group comparisons with children, the Quinton 410 provides acceptable blood pressure estimates resulting from a variety of events, including exercise.
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Kang, Il-seok, and Sung-mo Yang. "The Effect of Back Pressure Change on Exhaust Emissions According to the Confluence Geometry of a Dual Exhaust System in Idling." Applied Sciences 12, no. 4 (February 11, 2022): 1855. http://dx.doi.org/10.3390/app12041855.
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In this study, a pressure transducer was installed in an exhaust system to analyze the effect of the change in back pressure according to the change of the confluence geometry of an exhaust pipe system on an exhaust emission. In addition, to perform exhaust gas measurement, the system was warmed up for about 40 s on the chassis dynamometer, and exhaust gas and back pressure measurements were performed simultaneously. In the back pressure measurement results, it was possible to confirm the difference in back pressure according to the change in the confluence shape. In addition, it was also confirmed that there was a clear difference in the exhaust emission measurement result. In particular, the H-type exhaust pipe system showed the highest pressure in the exhaust pipe due to the influence of the confluence geometry. Due to this influence, THC showed the highest measured value in the exhaust emission result. However, the X-type exhaust pipe system showed the lowest pressure due to the influence of the confluence geometry. Due to this influence, the THC showed the lowest measured value in the exhaust emission result. Therefore, through the conclusion of this study, an optimal exhaust system to reduce THC was proposed, and the importance of back pressure in exhaust system design was confirmed.
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OKUTSU, I., I. HAMANAKA, and A. YOSHIDA. "Pre- and Postoperative Guyon’s Canal Pressure Change in Endoscopic Carpal Tunnel Release: Correlation with Transient Postoperative Guyon’s Canal Syndrome." Journal of Hand Surgery (European Volume) 34, no. 2 (March 12, 2009): 208–11. http://dx.doi.org/10.1177/1753193408100122.
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Perioperative Guyon’s canal and carpal canal pressure in one-forearm portal endoscopic carpal tunnel release surgery were measured in resting position and during active power gripping in 66 hands. This was done using the continuous infusion technique with a local anaesthetic and without pneumatic tourniquet. Immediate mean postoperative Guyon’s canal and carpal canal pressure decreased in both measurements. During active power gripping, postoperative Guyon’s canal pressure was less than 40 mmHg in 61 hands, however, this increased to over 40 mmHg in five hands. In these five hands, Guyon’s canal syndrome did not develop. Guyon’s canal and carpal canal pressures were only correlated during postoperative active power gripping. It remains unclear whether immediate postoperative Guyon’s canal pressure correlates with higher pressures a few days later as reported in cases of transient postoperative Guyon’s canal syndrome.
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THANGADURAI, P., A. CHANDRA BOSE, S. RAMASAMY, R. KESAVAMOORTHY, and T. R. RAVINDRAN. "HIGH PRESSURE EFFECTS ON ELECTRICAL RESISTIVITY AND DIELECTRIC PROPERTIES OF NANOCRYSTALLINE SnO2." International Journal of Nanoscience 05, no. 04n05 (August 2006): 471–77. http://dx.doi.org/10.1142/s0219581x06004656.
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Rutile structured nanocrystalline tin oxide (nano- SnO 2) was prepared by chemical precipitation method with different grain sizes. Its electrical and dielectric properties were studied using complex impedance spectroscopy under different hydrostatic pressures. These studies showed a transition in nano- SnO 2 under high-pressure. The transition pressures obtained from both the resistivity and dielectric measurements agree with each other and increase considerably with decrease in grain size. In order to find whether the transition under pressure is structural related or not, in situ high pressure Raman spectroscopy was done up to 3.38 GPa at room temperature. No structural change was observed and the transition may be due to the co-operative phenomenon of the change in band gap and better connectivity between grain boundaries.
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Skalak, T. C., and G. W. Schmid-Scho¨nbein. "Viscoelastic Properties of Microvessels in Rat Spinotrapezius Muscle." Journal of Biomechanical Engineering 108, no. 3 (August 1, 1986): 193–200. http://dx.doi.org/10.1115/1.3138602.
Повний текст джерелаАнотація:
In order to establish a quantitative model of blood flow in skeletal muscle, the mechanical properties of the blood vessels need to be measured. We present measurements of the viscoelastic properties of arterioles, venules, and capillaries in exteriorized rat spinotrapezius muscle. Muscles were perfused with an inert silicone polymer and a uniform static pressure was established by occlusion of the venous outflow. Vessel diameters were then measured as a function of the static pressure. This study provides the first measurements of the viscoelastic properties of microvessels in skeletal muscle in situ. Over a pressure range of 20–200 mmHg, the transverse arterioles are the most distensible vessels, while the arcade venules are the stiffest. In response to a step change in pressure, all vessels show an initial elastic deformation, followed by a nonlinear creep. Based on the experimental results for different pressure histories a constitutive equation relating vessel diameter to the local transmural pressure is proposed. Diameter changes are expressed in the form of a diameter strain, analogous to a Green’s strain, and are related to the local transmural pressure using a standard linear solid model. This model has only three empirical coefficients and could be fitted to all experimental results for all vessels within error of measurement.
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Alberding, Jonathan P., Ann L. Baldwin, Jennifer K. Barton, and Elizabeth Wiley. "Onset of pulsatile pressure causes transiently increased filtration through artery wall." American Journal of Physiology-Heart and Circulatory Physiology 286, no. 5 (May 2004): H1827—H1835. http://dx.doi.org/10.1152/ajpheart.01059.2003.
Повний текст джерелаАнотація:
Convective fluid motion through artery walls aids in the transvascular transport of macromolecules. Although many measurements of convective filtration have been reported, they were all obtained under constant transmural pressure. However, arterial pressure in vivo is pulsatile. Therefore, experiments were designed to compare filtration under steady and pulsatile pressure conditions. Rabbit carotid arteries were cannulated and excised from male New Zealand White rabbits anesthetized with pentobarbitol sodium (30 mg/kg iv administered). Hydraulic conductance was measured in cannulated excised rabbit carotid arteries at steady pressure. Next, pulsatile pressure trains were applied within the same vessels, and, simultaneously, arterial distension was monitored using Optical coherence tomography (OCT). For each pulse train, the volume of fluid lost through filtration was measured (subtracting volume change due to residual distension) and compared with that predicted from steady pressure measurements. At 60- and 80-mmHg baseline pressures, the experimental filtration volumes were significantly increased compared with those predicted for steady pressure ( P < 0.05). OCT demonstrated that the excess fluid volume loss was significantly greater than the volume that would be lost through residual distension ( P < 0.05). After 30 s, the magnitude of the excess of fluid loss was reduced. These results suggest that sudden onset of pulsatile pressure may cause changes in arterial interstitial hydration.
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Li, Baoxuan, Jianzhong Liu, Yufeng Li, Xiyu Zhu, and Hai-Hu Wen. "Pressure Induced Suppression to the Valence Change Transition in EuPdAs." Advances in Condensed Matter Physics 2015 (2015): 1–4. http://dx.doi.org/10.1155/2015/575421.
Повний текст джерелаАнотація:
By applying a hydrostatic pressure, we have successfully suppressed the valence change transition in EuPdAs. The studied compound EuPdAs crystallizes in a P63/mmc space group. Through resistivity and magnetic susceptibility measurements, we find that EuPdAs shows a phase transition at 180 K and another transition below 10 K at ambient pressure, as was reported before. The overall transport and magnetic behavior is to some extent similar to that of the parent phase of iron based superconductors. With application of a hydrostatic pressure, the transition at 180 K is sensitively suppressed with a pressure as low as 0.48 GPa. However, superconductivity has not been induced with pressure up to 1.90 GPa.
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Wang, Jia, Gang Peng, and Bao Jia Wu. "Phase Transition Study of CaB6 under High Pressure." Advanced Materials Research 705 (June 2013): 97–100. http://dx.doi.org/10.4028/www.scientific.net/amr.705.97.
Повний текст джерелаАнотація:
Phase transition of CaB6 sample under high pressure was studied by in situ electrical conductivity measurements and synchrotron X-ray diffraction up to 26GPa. Three anomalies in conductivity change were found respectively at 3.7, 12.4 and 21.9GPa. X-ray diffraction reveals that CaB6 transforms from Pm3m to orthogonal structure at 12.32GPa and hence the abnormal conductivity change at 12.4GPa can be attributed to the structural phase transition. The other two anomalies were considered as pressure-induced electronic phase transition in the pressure range of our measurements.
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Waheed, Nusrat, Mustafa Kamal, Shua Azam, Priyanka Priyanka, Hubdar Ali, Ayesha Kiran, and Abdul Hameed Talpur. "Effect of corneal cross linkage (CXL) on intraocular pressure (IOP) measurements in keratoconus patients." Advances in Ophthalmology & Visual System 12, no. 1 (May 13, 2022): 10–12. http://dx.doi.org/10.15406/aovs.2022.12.00409.
Повний текст джерелаАнотація:
This study aims to determine the effect of corneal cross-linkage (CXL) on intraocular pressure (IOP) in keratoconus patients. Methods: A quasi-experimental study was carried out at the Cornea Clinic of Al Ibrahim Eye Hospital Malir, Karachi. A total of 60 eyes of 36 subjects with progressive keratoconus with the age range of 15 to 31 years were fulfilling the criteria of the study. Subjects were selected with convenient sampling and subjects with a previous history of CXL were excluded from the study. A complete history of the patient, clinical examination with slit-lamp biomicroscopy, and visual acuity (VA) with Snellen chart were recorded. Intraocular pressure (IOP) measurements of each subject were recorded with Goldman Applanation Tonometer (GAT) before and immediately after 15 minutes of CXL and on the 2nd day of CXL, 1month, and 3 months after CXL. SPSS version 22 was used to analyze the data. Results: The average preoperative measured intraocular pressure (IOP) was 20.22 +/- 3.97 mmHg. There was a statistically significant decrease in IOP measurements 18.96 +/- 3.73 mmHg on the same day after the corneal cross linkage procedure with (P 0.001) while there was no statistically significant change in intraocular pressure (IOP) measurements was observed on the 2nd day, 1 month and 3 months after CXL. The postoperative mean of IOP measurements was 19.61 +/- 3.47 mmHg on the 2nd day, 19.67 +/- 3.14 mmHg on 1 month, and 19.33 +/- 3.64 mmHg at 3 months respectively. Conclusion: This study shows that reductions in intraocular pressure (IOP) measurements were observed on the immediate response of corneal cross-linkage (CXL) on the same day. This change might be due to immediate alteration in the biomechanics of the cornea during corneal cross-linkage. These changes return to the normal position later because no change was seen on different follow-ups of patients after CXL in eyes with keratoconus.
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Rahardjo, Harianto, and Delwyn G. Fredlund. "Experimental verification of the theory of consolidation for unsaturated soils." Canadian Geotechnical Journal 32, no. 5 (October 1, 1995): 749–66. http://dx.doi.org/10.1139/t95-074.
Повний текст джерелаАнотація:
An experimental program was designed to study the behavior of unsaturated soils during undrained loading and consolidation. A Ko cylinder was designed and built for the testing program. Simultaneous measurements of pore-air and pore-water pressures could be made throughout a soil specimen using this Ko cylinder. Four types of tests were performed on a silty sand. These are (1) undrained loading tests where both the air and water are not allowed to drain, (2) constant water content tests where only the water phase is not allowed to drain, (3) consolidation tests where both the air and water phases are allowed to drain, and (4) increasing matric suction tests. Undrained loading tests or constant water content loading tests were conducted for measuring the pore pressure parameters for the unsaturated soil. Drained tests consisting of either consolidation tests or increasing matric suction tests were conducted to study the pore pressure distribution and volume change behavior throughout an unsaturated soil during a transient process. The experimental pore pressure parameters obtained from the undrained loadings and constant water content leadings agreed reasonably well with theory. The pore-air pressure was found to dissipate instantaneously when the air phase is continuous. The pore-water pressure dissipation during the consolidation test was found to be faster than the pore-water pressure decrease during the increasing matric suction test. The differing rates of dissipation were attributed to the different coefficients of water volume change for each of the tests. The water volume changes during the consolidation test were considerably smaller than the water volume changes during the increasing matric suction tests for the same increment of pressure change. Key words : consolidation, Ko loading, matric suction, pore-air pressures, pore-water pressures, unsaturated soils
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Settembre, N., T. Kagayama, P. Kauhanen, P. Vikatmaa, Y. Inoue, and M. Venermo. "The Influence of Heating on Toe pressure in Patients with Peripheral Arterial Disease." Scandinavian Journal of Surgery 107, no. 1 (May 18, 2017): 62–67. http://dx.doi.org/10.1177/1457496917705994.
Повний текст джерелаАнотація:
Background and Aim: The toe skin temperature in vascular patients can be low, making reliable toe pressure measurements difficult to obtain. The aim of this study was to evaluate the effect of heating on the toe pressure measurements. Materials and Methods: A total of 86 legs were examined. Brachial pressure and toe pressure were measured at rest in a supine position using a laser Doppler device that also measured skin temperature. After heating the toes for 5 min with a heating pad, we re-measured the toe pressure. Furthermore, after heating the skin to 40° with the probe, toe pressures were measured a third time. Results: The mean toe skin temperature at the baseline measurement was 24.0 °C (standard deviation: 2.8). After heating the toes for 5 min with a warm heating pad, the skin temperature rose to a mean 27.8 °C (standard deviation: 2.8; p = 0.000). The mean toe pressure rose from 58.5 (standard deviation: 32) to 62 (standard deviation: 32) mmHg (p = 0.029). Furthermore, after the skin was heated up to 40 °C with the probe, the mean toe pressure in the third measurement was 71 (standard deviation: 34) mmHg (p = 0.000). The response to the heating varied greatly between the patients after the first heating—from −34 mmHg (toe pressure decreased from 74 to 40 mmHg) to +91 mmHg. When the toes were heated to 40 °C, the change in to toe pressure from the baseline varied between −28 and +103 mmHg. Conclusion: Our data indicate that there is a different response to the heating in different clinical situations and in patients with a different comorbidity.
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Iken, Almut, Kristian Fabri, and Martin Funk. "Water storage and subglacial drainage conditions inferred from borehole measurements on Gornergletscher, Valais, Switzerland." Journal of Glaciology 42, no. 141 (1996): 233–48. http://dx.doi.org/10.1017/s0022143000004093.
Повний текст джерелаАнотація:
AbstractMeasurements of change in length of a borehole, or displacements of poles and of subglacial Water pressure were combined with drainage tests and electrode tests in boreholes, in experiments near the northern margin of Gornergletscher, Valais, Switzerland, at the upstream side of an overdeepening. The measurements suggest that the subglacial drainage system consisted of discrete conduits at that location, presumably linked cavities on “clean” bedrock. Changes in subglacial water pressure were followed by variations in subglacial water storage, together with similar variations in elevation of a pole. The variations in subglacial water storage caused changes in cross-sections of subglacial passageways and thereby changed the frequencies of slug-test oscillations. Similar experiments conducted near the center line of the glacier revealed different subglacial conditions: impeded drainage through a sediment layer, and different depths of water levels in different boreholes. These results are discussed in relation to previous studies.
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Iken, Almut, Kristian Fabri, and Martin Funk. "Water storage and subglacial drainage conditions inferred from borehole measurements on Gornergletscher, Valais, Switzerland." Journal of Glaciology 42, no. 141 (1996): 233–48. http://dx.doi.org/10.3189/s0022143000004093.
Повний текст джерелаАнотація:
AbstractMeasurements of change in length of a borehole, or displacements of poles and of subglacial Water pressure were combined with drainage tests and electrode tests in boreholes, in experiments near the northern margin of Gornergletscher, Valais, Switzerland, at the upstream side of an overdeepening. The measurements suggest that the subglacial drainage system consisted of discrete conduits at that location, presumably linked cavities on “clean” bedrock. Changes in subglacial water pressure were followed by variations in subglacial water storage, together with similar variations in elevation of a pole. The variations in subglacial water storage caused changes in cross-sections of subglacial passageways and thereby changed the frequencies of slug-test oscillations. Similar experiments conducted near the center line of the glacier revealed different subglacial conditions: impeded drainage through a sediment layer, and different depths of water levels in different boreholes. These results are discussed in relation to previous studies.
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Ho, Chester H., Toula Bensitel, Xiaofeng Wang, and Kath M. Bogie. "Pulsatile Lavage for the Enhancement of Pressure Ulcer Healing: A Randomized Controlled Trial." Physical Therapy 92, no. 1 (January 1, 2012): 38–48. http://dx.doi.org/10.2522/ptj.20100349.
Повний текст джерелаАнотація:
Background Pressure ulcer development is a common, serious complication after spinal cord injury (SCI). Although many biophysical agents are available for treatment, few randomized controlled trials of their efficacy have been done. Objective The study objective was to examine the efficacy of low-pressure pulsatile lavage treatment for stage III and IV pressure ulcers in people with SCI. Design This study was a randomized controlled trial. Participants and assessors were unaware of intervention assignments. Setting This study was conducted in an SCI tertiary care center inpatient unit. Participants Participants were 28 people with SCI and stage III and IV pelvic pressure ulcers; 14 participants each were randomly assigned to treatment and control (sham treatment) groups. Intervention Daily low-pressure pulsatile lavage treatment with 1 L of normal saline at 11 psi of pressure was applied to the treatment group along with standard dressing changes. The control group received only sham treatment and standard dressing changes. Measurements Linear and volume measurements of pressure ulcer dimensions were obtained weekly for 3 weeks. Results Statistical analysis with the t test revealed no statistically significant difference in demographics between groups. Random-coefficient models for analysis of linear and volume measurements revealed improvements over time for both groups. Time trend analysis revealed greater measurement decreases for the treatment group. Differences in rates of change (with 95% confidence intervals) for treatment and control groups, respectively, were: depth, −0.24 (0.09 to −0.58) cm/wk; width, −0.16 (0.06 to −0.39) cm/wk; length, −0.47 (0.18 to −1.12) cm/wk; and volume, −0.33 (0.13 to −0.80) cm3/wk. Limitations Study limitations were small sample size and inclusion of only one site. Additionally, participants were not queried about their group assignments. Conclusions Pulsatile lavage enhanced stage III and IV pelvic pressure ulcer healing rates in people with SCI relative to standard pressure ulcer treatment alone.