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1
Staubli, Thomas, and Donald Rockwell. "Pressure fluctuations on an oscillating trailing edge." Journal of Fluid Mechanics 203 (June 1989): 307–46. http://dx.doi.org/10.1017/s0022112089001485.
Повний текст джерелаАнотація:
Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability at f0 by controlled oscillations of the edge at fe produces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequency f0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component at f0 and resonant peaking of the component at fe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift at fe and f0 acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location at fe; that at f0 is invariant. Moreover, the mean location of the lift at fe undergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequencies f0 and fe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.
2
Мартынец, Татьяна Викторовна. "Experimental research of oscillating modulation of pressure in hydraulic brake drive." Eastern-European Journal of Enterprise Technologies 2, no. 10(56) (April 1, 2012): 46–49. http://dx.doi.org/10.15587/1729-4061.2012.3893.
Повний текст джерела
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Marsh, Donald J., Olga V. Sosnovtseva, Alexey N. Pavlov, Kay-Pong Yip, and Niels-Henrik Holstein-Rathlou. "Frequency encoding in renal blood flow regulation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288, no. 5 (May 2005): R1160—R1167. http://dx.doi.org/10.1152/ajpregu.00540.2004.
Повний текст джерелаАнотація:
With a model of renal blood flow regulation, we examined consequences of tubuloglomerular feedback (TGF) coupling to the myogenic mechanism via voltage-gated Ca channels. The model reproduces the characteristic oscillations of the two mechanisms and predicts frequency and amplitude modulation of the myogenic oscillation by TGF. Analysis by wavelet transforms of single-nephron blood flow confirms that both amplitude and frequency of the myogenic oscillation are modulated by TGF. We developed a double-wavelet transform technique to estimate modulation frequency. Median value of the ratio of modulation frequency to TGF frequency in measurements from 10 rats was 0.95 for amplitude modulation and 0.97 for frequency modulation, a result consistent with TGF as the modulating signal. The simulation predicted that the modulation was regular, while the experimental data showed much greater variability from one TGF cycle to the next. We used a blood pressure signal recorded by telemetry from a conscious rat as the input to the model. Blood pressure fluctuations induced variability in the modulation records similar to those found in the nephron blood flow results. Frequency and amplitude modulation can provide robust communication between TGF and the myogenic mechanism.
4
Teixeira, Luis Augusto, Joane de Figueiredo Serpa Coutinho, and Daniel Boari Coelho. "Regulation of dynamic postural control to attend manual steadiness constraints." Journal of Neurophysiology 120, no. 2 (August 1, 2018): 693–702. http://dx.doi.org/10.1152/jn.00941.2017.
Повний текст джерелаАнотація:
In daily living activities, performance of spatially accurate manual movements in upright stance depends on postural stability. In the present investigation, we aimed to evaluate the effect of the required manual steadiness (task constraint) on the regulation of dynamic postural control. A single group of young participants ( n = 20) were evaluated in the performance of a dual posturo-manual task of balancing on a platform oscillating in sinusoidal translations at 0.4-Hz (low) or 1-Hz (high) frequencies while stabilizing a cylinder on a handheld tray. Manual task constraint was manipulated by comparing the conditions of keeping the cylinder stationary on its flat or round side, corresponding to low and high manual task constraints, respectively. Results showed that in the low oscillation frequency the high manual task constraint led to lower oscillation amplitudes of the head, center of mass, and tray, in addition to higher relative phase values between ankle/hip-shoulder oscillatory rotations and between center of mass/center of pressure-feet oscillations as compared with values observed in the low manual task constraint. Further analyses showed that the high manual task constraint also affected variables related to both postural (increased amplitudes of center of pressure oscillation) and manual (increased amplitude of shoulder rotations) task components in the high oscillation frequency. These results suggest that control of a dynamic posturo-manual task is modulated in distinct parameters to attend the required manual steadiness in a complex and flexible way. NEW & NOTEWORTHY We evaluated dynamic postural control on a platform oscillating in sinusoidal translations at different frequencies while performing a manual task with low or high steadiness constraints. Results showed that high manual task constraint led to modulation of metric and coordination variables associated with greater postural stability. Our findings suggest that motor control is regulated in an integrative mode at the posturo-manual task level, with reciprocal interplay between the postural and manual components.
5
Horsman, H. M., K. C. Peebles, and Y. C. Tzeng. "Interactions between breathing rate and low-frequency fluctuations in blood pressure and cardiac intervals." Journal of Applied Physiology 119, no. 7 (October 1, 2015): 793–98. http://dx.doi.org/10.1152/japplphysiol.00525.2015.
Повний текст джерелаАнотація:
Evidence derived from spontaneous measures of cardiovagal baroreflex sensitivity (BRS) suggests that slow breathing at 6 breaths/min augments BRS. However, increases in BRS associated with slow breathing may simply reflect the frequency-dependent nature of the baroreflex rather than the modulation of baroreflex function by changes in breathing rate per se. To test this hypothesis we employed a crossover study design ( n = 14) wherein breathing rate and systolic arterial blood pressure (SAP) oscillation induced via the application of oscillating lower body negative pressure (OLBNP) were independently varied at fixed frequencies. Breathing rate was controlled at 6 or 10 breaths/min with the aid of a metronome, and SAP oscillations were driven at 0.06 Hz and 0.1 Hz using OLBNP. The magnitudes of SAP and R-R interval (cardiac period) oscillations were quantified using power spectral analysis, and the transfer function gain between SAP and R-R interval was used to estimate BRS. Linear mixed-effects models were used to examine the main effects and interactions between breathing rate and OLBNP frequency. There was no statistical interaction between breathing and OLBNP frequency ( P = 0.59), indicating that the effect of breathing rate on BRS did not differ according to OLBNP frequency (and vice versa). Additionally, there was no main effect for breathing rate ( P = 0.28). However, we observed a significant main effect for OLBNP frequency ( P = 0.01) consistent with the frequency-dependent nature of baroreflex. These findings suggest that increases in spectral indices of BRS reflect the frequency dependence of the baroreflex and are not due to slow breathing per se.
6
Kalashnik, M. V., and S. N. Kulichkov. "On pressure perturbations caused by a moving heat source of the frontal type (hydrostatic mode)." Известия Российской академии наук. Физика атмосферы и океана 55, no. 5 (November 25, 2019): 51–61. http://dx.doi.org/10.31857/s0002-351555551-61.
Повний текст джерелаАнотація:
The problem of perturbations of the surface pressure caused by a moving nonstationary frontal heat source (localized along one horizontal coordinate) is considered. Pressure disturbances are associated with internal gravity waves (IGWs). It is shown that when a source moves in a finite-height atmospheric layer (atmospheric waveguide) when a discrete set of vertical IGW modes is excited, there are three types of temporal variation of surface pressure at a fixed observation point. These types correspond respectively to the time signal with amplitude modulation, the signal with frequency modulated Doppler type and the signal that occurs only after passing through the source. Each type is implemented for specific values of the oscillation frequency of the source and the Mach number (the ratio of the speed of the source to the phase velocity of the IGW). At Mach numbers less than one, an oscillating source always excites wave precursors disturbances observed before the source arrives. The movement of the source in a semi-infinite atmosphere leads to additional excitation of waves that transfer energy to the upper layers of the atmosphere.
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Chen, C. K., L. Wang, J. T. Yang, and L. T. Chen. "Experimental and Computational Analysis of Periodic Flow Structure in Oscillatory Gas Flow Meters." Journal of Mechanics 22, no. 2 (June 2006): 137–44. http://dx.doi.org/10.1017/s1727719100004433.
Повний текст джерелаАнотація:
AbstractThe oscillatory characteristics and dynamic structure of periodic flow in an oscillatory gas flow meter were studied experimentally and numerically. The flow oscillations were triggered by the Coanda effect and an universal correlation between Strouhal number and Reynolds number, Str = 1.09 × 10−3 for ReHD >800, was deduced based on spectral analysis of the pressure fluctuations in the flow channel. Numerical simulation indicated that the evolution of the flow patterns was classified into stages of induction and sustainable periodic oscillation. The transformation between the two stages was noticeably affected by the design of the feedback channels. The results further revealed that the development of the main vortex in the oscillating chamber and the small vortices at the entrance of the feedback channels concurrently modulate the mechanism of oscillation. The small vortices located at both entrances of the feedback channels play the role of a pair of modulating valves, which alternatively switch on and off the bypass flow through each feedback channel, thus reinforcing the periodic oscillation.
8
Lester, Rosemary A., and Brad H. Story. "Acoustic Characteristics of Simulated Respiratory-Induced Vocal Tremor." American Journal of Speech-Language Pathology 22, no. 2 (May 2013): 205–11. http://dx.doi.org/10.1044/1058-0360(2012/12-0043).
Повний текст джерелаАнотація:
Purpose The purpose of this study was to investigate the relation of respiratory forced oscillation to the acoustic characteristics of vocal tremor. Method Acoustical analyses were performed to determine the characteristics of the intensity and fundamental frequency (F 0 ) for speech samples obtained by Farinella, Hixon, Hoit, Story, and Jones (2006) using a respiratory forced oscillation paradigm with 5 healthy adult males to simulate vocal tremor involving respiratory pressure modulation. The analyzed conditions were sustained productions of /a/ with amplitudes of applied pressure of 0, 1, 2, and 4 cmH 2 O and a rate of 5 Hz. Results Forced oscillation of the respiratory system produced modulation of the intensity and F 0 for all participants. Variability was observed between participants and conditions in the change in intensity and F 0 per unit of pressure change, as well as in the mean intensity and F 0 . However, the extent of modulation of intensity and F 0 generally increased as the applied pressure increased, as would be expected. Conclusion These findings suggest that individuals develop idiosyncratic adaptations to pressure modulations, which are important to understanding aspects of variability in vocal tremor, and highlight the need to assess all components of the speech mechanism that may be directly or indirectly affected by tremor.
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Amador, Ana, Franz Goller, and Gabriel B. Mindlin. "Frequency Modulation During Song in a Suboscine Does Not Require Vocal Muscles." Journal of Neurophysiology 99, no. 5 (May 2008): 2383–89. http://dx.doi.org/10.1152/jn.01002.2007.
Повний текст джерелаАнотація:
The physiology of sound production in suboscines is poorly investigated. Suboscines are thought to develop song innately unlike the closely related oscines. Comparing phonatory mechanisms might therefore provide interesting insight into the evolution of vocal learning. Here we investigate sound production and control of sound frequency in the Great Kiskadee ( Pitangus sulfuratus) by recording air sac pressure and vocalizations during spontaneously generated song. In all the songs and calls recorded, the modulations of the fundamental frequency are highly correlated to air sac pressure. To test whether this relationship reflects frequency control by changing respiratory activity or indicates synchronized vocal control, we denervated the syringeal muscles by bilateral resection of the tracheosyringeal nerve. After denervation, the strong correlation between fundamental frequency and air sac pressure patterns remained unchanged. A single linear regression relates sound frequency to air sac pressure in the intact and denervated birds. This surprising lack of control by syringeal muscles of frequency in Kiskadees, in strong contrast to songbirds, poses the question of how air sac pressure regulates sound frequency. To explore this question theoretically, we assume a nonlinear restitution force for the oscillating membrane folds in a two mass model of sound production. This nonlinear restitution force is essential to reproduce the frequency modulations of the observed vocalizations.
10
Grisk, Olaf, and Harald M. Stauss. "Frequency modulation of mesenteric and renal vascular resistance." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 282, no. 5 (May 1, 2002): R1468—R1476. http://dx.doi.org/10.1152/ajpregu.00307.2001.
Повний текст джерелаАнотація:
The hypothesis was tested that low-frequency vasomotions in individual vascular beds are integrated by the cardiovascular system, such that new fluctuations at additional frequencies occur in arterial blood pressure. In anesthetized rats ( n = 8), the sympathetic splanchnic and renal nerves were simultaneously stimulated at combinations of frequencies ranging from 0.075 to 0.8 Hz. Blood pressure was recorded together with mesenteric and renal blood flow velocities. Dual nerve stimulation at low frequencies (<0.6 Hz) caused corresponding oscillations in vascular resistance and blood pressure, whereas higher stimulation frequencies increased the mean levels. Blood pressure oscillations were only detected at the individual stimulation frequencies and their harmonics. The strongest periodic responses in vascular resistance were found at 0.40 ± 0.02 Hz in the mesenteric and at 0.32 ± 0.03 Hz ( P < 0.05) in the renal vascular bed. Thus frequency modulation of low-frequency vasomotions in individual vascular beds does not cause significant blood pressure oscillations at additional frequencies. Furthermore, our data suggest that sympathetic modulation of mesenteric vascular resistance can initiate blood pressure oscillations at slightly higher frequencies than sympathetic modulation of renal vascular resistance.
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Siu, K. L., B. Sung, W. A. Cupples, L. C. Moore, and K. H. Chon. "Detection of low-frequency oscillations in renal blood flow." American Journal of Physiology-Renal Physiology 297, no. 1 (July 2009): F155—F162. http://dx.doi.org/10.1152/ajprenal.00114.2009.
Повний текст джерелаАнотація:
Detection of the low-frequency (LF; ∼0.01 Hz) component of renal blood flow, which is theorized to reflect the action of a third renal autoregulatory mechanism, has been difficult due to its slow dynamics. In this work, we used three different experimental approaches to detect the presence of the LF component of renal autoregulation using normotensive and spontaneously hypertensive rats (SHR), both anesthetized and unanesthetized. The first experimental approach utilized a blood pressure forcing in the form of a chirp, an oscillating perturbation with linearly increasing frequency, to elicit responses from the LF autoregulatory component in anesthetized normotensive rats. The second experimental approach involved collection and analysis of spontaneous blood flow fluctuation data from anesthetized normotensive rats and SHR to search for evidence of the LF component in the form of either amplitude or frequency modulation of the myogenic and tubuloglomerular feedback mechanisms. The third experiment used telemetric recordings of arterial pressure and renal blood flow from normotensive rats and SHR for the same purpose. Our transfer function analysis of chirp signal data yielded a resonant peak centered at 0.01 Hz that is greater than 0 dB, with the transfer function gain attenuated to lower than 0 dB at lower frequencies, which is a hallmark of autoregulation. Analysis of the data from the second experiments detected the presence of ∼0.01-Hz oscillations only with isoflurane, albeit at a weaker strength compared with telemetric recordings. With the third experimental approach, the strength of the LF component was significantly weaker in the SHR than in the normotensive rats. In summary, our detection via the amplitude modulation approach of interactions between the LF component and both tubuloglomerular feedback and the myogenic mechanism, with the LF component having an identical frequency to that of the resonant gain peak, provides evidence that 0.01-Hz oscillations may represent the third autoregulatory mechanism.
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Auer, M. P., C. Gebauer, K. G. Mösl, C. Hirsch, and T. Sattelmayer. "Active Instability Control: Feedback of Combustion Instabilities on the Injection of Gaseous Fuel." Journal of Engineering for Gas Turbines and Power 127, no. 4 (March 1, 2004): 748–54. http://dx.doi.org/10.1115/1.1924718.
Повний текст джерелаАнотація:
Modern low-emission premix combustion systems are often susceptible to combustion instabilities. Active instability control (AIC) systems are commonly used to attenuate these oscillations. For the control authority of AIC systems the effective amplitude and phase of the fuel modulation at the fuel outlet are as critical as the proper injection position. In typical cases the modulation of the fuel at the location of the actuator can be fundamentally different in amplitude and phase from the modulation of the fuel flow at the fuel outlet. In addition to the well-known effects stemming from the acoustics and Mach number of the fuel system, the fuel flow in the fuel system is also modulated by the oscillation of the pressure in the combustor in case of combustion instabilities. The superposition of the upstream modulation by the actuator and the modulation downstream by the combustion instability can result in an unexpected behavior of the fuel injection, from total compensation of the modulation to very high oscillations in the resonant case, accompanied by drastic phase shifts. This paper describes the influence of the secondary fuel modulation because of the combustion instability on the control authority of AIC systems on the basis of theoretical considerations and measurements for an atmospheric test rig with a natural gas-fired swirl burner.
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Thomas, Christian, Andrew P. Bassom, P. J. Blennerhassett, and Christopher Davies. "The linear stability of oscillatory Poiseuille flow in channels and pipes." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, no. 2133 (April 13, 2011): 2643–62. http://dx.doi.org/10.1098/rspa.2010.0468.
Повний текст джерелаАнотація:
The linear stability of confined, periodic, parallel fluid flows is examined. The flow fields considered consist of a steady pressure gradient-driven velocity field combined with a purely oscillatory component generated by either an oscillatory pressure gradient or by harmonically oscillating bounding surfaces. Plane channel and circular pipe geometries are studied and all possible combinations of the steady and oscillatory flow components investigated. Neutral stability curves and critical conditions for instability are computed for a selection of steady–unsteady velocity ratios, channel half-widths and pipe radii. The results obtained confirm previous investigations into the effects of small amounts of periodic modulation on the linear stability of the underlying steady flow, but provide much more comprehensive information on the linear stability regions of unsteady parallel flows in channels and pipes.
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Xu, Xiang, Chen Zhou, Run Shi, Binbin Ni, Zhengyu Zhao, and Yuannong Zhang. "Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes." Annales Geophysicae 34, no. 9 (September 21, 2016): 815–29. http://dx.doi.org/10.5194/angeo-34-815-2016.
Повний текст джерелаАнотація:
Abstract. Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.
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Broten, T. P., and J. E. Zehr. "Autonomic modulation of ultradian blood pressure and heart rate oscillations in dogs." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, no. 5 (May 1, 1989): R1127—R1137. http://dx.doi.org/10.1152/ajpregu.1989.256.5.r1127.
Повний текст джерелаАнотація:
Autonomic receptor modulation of ultradian oscillations of blood pressure and heart rate was studied in telemetered free-running dogs. Data, analyzed for their harmonic content by fast Fourier transform (FFT) methods, indicated that ultradian and circadian oscillations of 22.9 +/- 2.5 and 10.5 +/- 0.9 (SD) mmHg, respectively, were present. The average principal frequency for the ultradian oscillations in 12 dogs was 0.760 +/- 0.11 cycles/h for arterial pressure and 0.808 +/- 0.10 for heart rate. Atropine had no effect on periodicity of either arterial pressure or heart rate. Metoprolol, a beta 1-antagonist, or hexamethonium, a ganglionic blocker, significantly reduced the power of both arterial pressure and heart rate (P less than 0.05), whereas the primary frequencies of both were unchanged. Prazosin, an alpha 1-blocker, sharply reduced arterial pressure power (P less than 0.05) and increased the power of heart rate (P less than 0.05), demonstrating that it is possible to uncouple arterial pressure oscillations from influences of heart rate. We conclude that the sympathetic limb of the autonomic nervous system is primarily responsible for these oscillations and that vagal influences on the heart partially dampen these rhythms.
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Schmidt, J. A., P. Borgstrom, and M. Intaglietta. "Neurogenic modulation of periodic hemodynamics in rabbit skeletal muscle." Journal of Applied Physiology 75, no. 3 (September 1, 1993): 1216–21. http://dx.doi.org/10.1152/jappl.1993.75.3.1216.
Повний текст джерелаАнотація:
We characterized the effect of various forms of neural blockade and vasopressin infusion on regular slow-wave flux oscillation (RSWFO). RSWFO, measured with laser-Doppler flowmetry (LDF), was induced by local reduction of arterial pressure in the gastrocnemius muscle of 30 New Zealand White rabbits. At normal median femoral arterial mean pressure, LDF only showed irregular variations. With an intact innervation, RSWFO was maximal at a median femoral mean pressure of 30 mmHg (range 25–53), the median frequency was 1.7 cycles/min (range 1.0–3.0), and the maximum amplitude was 50% (range 19–119). Application of lidocaine to the sciatic nerve, or cutting of this nerve, when arterial pressure was reduced, resulted in disappearance of slow waves in all cases. Intravenous application of guanethidine resulted in a significant reduction of the flux oscillation amplitude from 47 to 10% (P < 0.001). In an additional nine animals with sciatic denervation and local blood pressure reduction, RSWFO could be induced by intravenous vasopressin infusion. These results offer a new pathophysiological concept of periodic hemodynamics as a locally controlled and, with intact innervation, a neurally modulated mechanism for blood flow redistribution in cases of reduced blood pressure and flow.
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Badra, Leslie J., William H. Cooke, Jeffrey B. Hoag, Alexandra A. Crossman, Tom A. Kuusela, Kari U. O. Tahvanainen, and Dwain L. Eckberg. "Respiratory modulation of human autonomic rhythms." American Journal of Physiology-Heart and Circulatory Physiology 280, no. 6 (June 1, 2001): H2674—H2688. http://dx.doi.org/10.1152/ajpheart.2001.280.6.h2674.
Повний текст джерелаАнотація:
We studied the influence of three types of breathing [spontaneous, frequency controlled (0.25 Hz), and hyperventilation with 100% oxygen] and apnea on R-R interval, photoplethysmographic arterial pressure, and muscle sympathetic rhythms in nine healthy young adults. We integrated fast Fourier transform power spectra over low (0.05–0.15 Hz) and respiratory (0.15–0.3 Hz) frequencies; estimated vagal baroreceptor-cardiac reflex gain at low frequencies with cross-spectral techniques; and used partial coherence analysis to remove the influence of breathing from the R-R interval, systolic pressure, and muscle sympathetic nerve spectra. Coherence among signals varied as functions of both frequency and time. Partialization abolished the coherence among these signals at respiratory but not at low frequencies. The mode of breathing did not influence low-frequency oscillations, and they persisted during apnea. Our study documents the independence of low-frequency rhythms from respiratory activity and suggests that the close correlations that may exist among arterial pressures, R-R intervals, and muscle sympathetic nerve activity at respiratory frequencies result from the influence of respiration on these measures rather than from arterial baroreflex physiology. Most importantly, our results indicate that correlations among autonomic and hemodynamic rhythms vary over time and frequency, and, thus, are facultative rather than fixed.
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Marsh, Donald J., Olga V. Sosnovtseva, Ki H. Chon, and Niels-Henrik Holstein-Rathlou. "Nonlinear interactions in renal blood flow regulation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288, no. 5 (May 2005): R1143—R1159. http://dx.doi.org/10.1152/ajpregu.00539.2004.
Повний текст джерелаАнотація:
We have developed a model of tubuloglomerular feedback (TGF) and the myogenic mechanism in afferent arterioles to understand how the two mechanisms are coupled. This paper presents the model. The tubular model predicts pressure, flow, and NaCl concentration as functions of time and tubular length in a compliant tubule that reabsorbs NaCl and water; boundary conditions are glomerular filtration rate (GFR), a nonlinear outflow resistance, and initial NaCl concentration. The glomerular model calculates GFR from a change in protein concentration using estimates of capillary hydrostatic pressure, tubular hydrostatic pressure, and plasma flow rate. The arteriolar model predicts fraction of open K channels, intracellular Ca concentration (Cai), potential difference, rate of actin–myosin cross bridge formation, force of contraction, and length of elastic elements, and was solved for two arteriolar segments, identical except for the strength of TGF input, with a third, fixed resistance segment representing prearteriolar vessels. The two arteriolar segments are electrically coupled. The arteriolar, glomerular, and tubular models are linked; TGF modulates arteriolar circumference, which determines vascular resistance and glomerular capillary pressure. The model couples TGF input to voltage-gated Ca channels. It predicts autoregulation of GFR and renal blood flow, matches experimental measures of tubular pressure and macula densa NaCl concentration, and predicts TGF-induced oscillations and a faster smaller vasomotor oscillation. There are nonlinear interactions between TGF and the myogenic mechanism, which include the modulation of the frequency and amplitude of the myogenic oscillation by TGF. The prediction of modulation is confirmed in a companion study ( 28 ).
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Leung, C. G., and P. Mason. "Spectral analysis of arterial blood pressure and raphe magnus neuronal activity in anesthetized rats." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 271, no. 2 (August 1, 1996): R483—R489. http://dx.doi.org/10.1152/ajpregu.1996.271.2.r483.
Повний текст джерелаАнотація:
Recent evidence suggests that nociceptive modulatory cells in the nucleus raphe magnus (RM) and adjacent nucleus reticularis magnocellularis (NRMC) may participate in the modulation of autonomic processing. Therefore, spectral analyses were used to determine component frequencies common to both arterial blood pressure and the activity of RM/NRMC neurons in rats lightly anesthetized with isoflurane. These analyses detected powerful, extremely low frequency (period length: 6.4-18.5 min) oscillations in arterial blood pressure and in the activity of two classes of RM/NRMC neurons, ON and OFF cells. All ON cells discharged during periods of low blood pressure, whereas all OFF cells discharged during periods of high blood pressure. In contrast, the discharge of NEUTRAL and REGULAR cells did not have a consistent relationship to blood pressure. The role of these cells in nociceptive modulation is also unclear. The results presented indicate that ON and OFF cells may participate in the modulation of both autonomic and nociceptive processing.
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Brady, Ken M., R. Blaine Easley, Kathleen Kibler, David W. Kaczka, Dean Andropoulos, Charles D. Fraser, Peter Smielewski, et al. "Positive end-expiratory pressure oscillation facilitates brain vascular reactivity monitoring." Journal of Applied Physiology 113, no. 9 (November 1, 2012): 1362–68. http://dx.doi.org/10.1152/japplphysiol.00853.2012.
Повний текст джерелаАнотація:
The pressure reactivity index (PRx) identifies optimal cerebral perfusion pressure after traumatic brain injury. We describe a method to improve PRx precision by induced variations in arterial blood pressure (ABP) using positive end-expiratory pressure (PEEP) modulation ( iPRx). Neonatal swine ( n = 10) were ventilated with static PEEP and then with PEEP oscillated between 5 and 10 cmH2O at a frequency of 1/min. PRx was recorded as a moving correlation coefficient between ABP and intracranial pressure (ICP) from spontaneous ABP activity (0.05-0.003 Hz) during static PEEP. iPRx was similarly recorded with PEEP oscillation-induced ABP waves. The lower limit of autoregulation (LLA) was delineated with continuous cortical laser Doppler flux monitoring. PEEP oscillation increased autoregulation-monitoring precision. The ratios of median absolute deviations to range of possible values for the PRx and iPRx were 9.5% (8.3–13.7%) and 6.2% (4.2–8.7%), respectively ( P = 0.006; median, interquartile range). The phase-angle difference between ABP and ICP above LLA was 161° (150°–166°) and below LLA, −31° (−42° to 12°, P < 0.0001). iPRx above LLA was −0.42 (−0.67 to −0.29) and below LLA, 0.32 (0.22–0.43, P = 0.0004). A positive iPRx was 97% specific and 91% sensitive for perfusion pressure below LLA. PEEP oscillation caused stable, low-frequency ABP oscillations that reduced noise in the PRx. Safe translation of these findings to clinical settings is expected to yield more accurate and rapid delineation of individualized optimal perfusion-pressure goals for patients.
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He, Shengping, and Huijun Wang. "Oscillating Relationship between the East Asian Winter Monsoon and ENSO." Journal of Climate 26, no. 24 (December 2, 2013): 9819–38. http://dx.doi.org/10.1175/jcli-d-13-00174.1.
Повний текст джерелаАнотація:
Abstract This work investigates the interdecadal variations of the relationship between the El Niño–Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM), further explores possible mechanisms, and finally considers a recent switch in the ENSO–EAWM relationship. The 23-yr sliding correlation between the Niño-3.4 index and the EAWM index reveals an obvious low-frequency oscillation with a period of about 50 yr in the ENSO–EAWM relationship. Warm ENSO events during high-correlation periods are associated with an unusually weak East Asian trough, a positive phase of the North Pacific Oscillation (NPO), significant southerly wind anomalies along coastal East Asia, and warmer East Asian continent and adjacent oceans. However, there are no robust and significant anomalies in the EAWM-related circulation during low-correlation periods. Because of the southeastward shift of the Walker circulation, the area of anomalously high pressure in the western Pacific retreats south of 25°N, confining it to the region of the Philippine Sea. In this sense, the Pacific–East Asian teleconnection is not well established. Consequently, ENSO’s impact on the EAWM is suppressed. Additionally, the low-frequency oscillation of the ENSO–EAWM relationship might be attributable to the combined effect of the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation owing to their modulation on the establishment of the NPO teleconnection. The observation of two full cycles of the ENSO–EAWM relationship, a transition to negative PDO in the early 2000s and an enhancement of the Walker circulation in the late 1990s, suggests a recovery of the ENSO–EAWM relationship.
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Passino, C., P. Sleight, F. Valle, G. Spadacini, S. Leuzzi, and L. Bernardi. "Lack of peripheral modulation of cardiovascular central oscillatory autonomic activity during apnea in humans." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 1 (January 1, 1997): H123—H129. http://dx.doi.org/10.1152/ajpheart.1997.272.1.h123.
Повний текст джерелаАнотація:
Respiratory sinus arrhythmia (RSA) high-frequency oscillations (HF) and slow fluctuations in heart rate (LF) are thought to result from entrainment of a medullary oscillator, from the baroreflex, or from a combination of both central and baroreflex mechanisms. We sought to distinguish between the alternatives by examining with spectral analysis the behavior of heart rate (R-R interval) and blood pressure in 10 healthy subjects (mean age 27 +/- 1 yr) during apnea, altering the rate of preapnea entrainment stimuli by changing the frequency either of respiration (controlled at 0.1 or 0.25 Hz) or of baroreceptor stimulation by sinusoidal neck suction (0 to -30 mmHg, 0.1 or 0.2 Hz). During apnea the RSA-EF power decreased (from 6.73 +/- 0.15 to 3.67 +/- 0.10 In ms2: P < 0.0001), regardless of preapnea conditions, whereas LF power was reduced only if preceded by 0.1-Hz respiration or neck suction [from 8.71 +/- 0.18 to 6.52 +/- 0.11 In ms2 (P < 0.001) and from 8.31 +/- 0.23 to 6.90 +/- 0.38 In ms2 (P < 0.01), respectively]. The LF frequency seen in the R-R interval during apnea was slower than the spontaneous LF during 0.25-Hz breathing (0.082 +/- 0.01 vs. 0.112 +/- 0.001 Hz, P < 0.001), but the maneuvers during preapnea had no influence on the observed frequency or other characteristics of the slow oscillations during apnea. Moreover, we found no evidence of a progressive decrease in the power of the oscillation during apnea. The same behavior was observed on the mean blood pressure signal. In conclusion, a slow rhythm is present during apnea. In healthy subjects at rest the characteristics of this oscillation indicate that it could be generated by a central oscillator this may thus contribute to the origin of LF present during normal respiration, in addition to the baroreflex.
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Warner, M. R., J. M. deTarnowsky, C. C. Whitson, and J. M. Loeb. "Beat-by-beat modulation of AV conduction. II. Autonomic neural mechanisms." American Journal of Physiology-Heart and Circulatory Physiology 251, no. 6 (December 1, 1986): H1134—H1142. http://dx.doi.org/10.1152/ajpheart.1986.251.6.h1134.
Повний текст джерелаАнотація:
We examined the mechanism by which autonomic neural activity associated with respiration and blood pressure modulates atrioventricular (AV) conduction in conscious dogs. Mongrel dogs were anesthetized and instrumented under sterile conditions to record atrial and ventricular electrograms and blood pressure. In the conscious state, electrocardiogram (ECG), respiration, blood pressure, and electrograms were recorded continuously, and heart rate and AV interval were plotted graphically as a function of time. To delineate the role(s) of sympathetic and parasympathetic activity, AV conduction was studied during abrupt and linear changes in heart rate after administration of atropine, propranolol, or both. In the basal state and after propranolol, AV interval oscillated with respiration both in the absence of atrial pacing and at pacing rates 10–100 beats/min above control. Following atropine, oscillations in AV interval associated with respiration were abolished; however, linear and abrupt heart rate increases resulted in AV conduction changes that were associated with fluctuations in blood pressure. In contrast, after both atropine and propranolol, alterations in blood pressure or respiration did not influence AV conduction and rate-dependent prolongation of AV conduction occurred. We conclude that in the basal state, AV conduction is influenced predominately by changes in parasympathetic activity which is the major determinant of respiratory-related AV interval oscillations; after atropine, sympathetic activity produces fluctuations in both AV conduction and blood pressure; and intrinsic rate-dependent properties of the AV node are modulated continually by both divisions of the autonomic nervous system.
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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.
Повний текст джерелаАнотація:
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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Cui, Lihua, Fei Ma, and Tengfei Cai. "Investigation of Pressure Oscillation and Cavitation Characteristics for Submerged Self-Resonating Waterjet." Applied Sciences 11, no. 15 (July 29, 2021): 6972. http://dx.doi.org/10.3390/app11156972.
Повний текст джерелаАнотація:
The cavitation phenomenon of the self-resonating waterjet for the modulation of erosion characteristics is investigated in this paper. A three-dimensional computational fluid dynamics (CFD) model was developed to analyze the unsteady characteristics of the self-resonating jet. The numerical model employs the mixture two-phase model, coupling the realizable turbulence model and Schnerr–Sauer cavitation model. Collected data from experimental tests were used to validate the model. Results of numerical simulations and experimental data frequency bands obtained by the Fast Fourier transform (FFT) method were in very good agreement. For better understanding the physical phenomena, the velocity, the pressure distributions, and the cavitation characteristics were investigated. The obtained results show that the sudden change of the flow velocity at the outlet of the nozzle leads to the forms of the low-pressure zone. When the pressure at the low-pressure zone is lower than the vapor pressure, the cavitation occurs. The flow field structure of the waterjet can be directly perceived through simulation, which can provide theoretical support for realizing the modulation of the erosion characteristics, optimizing nozzle structure.
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Gunst, S. J., J. Q. Stropp, and J. Service. "Mechanical modulation of pressure-volume characteristics of contracted canine airways in vitro." Journal of Applied Physiology 68, no. 5 (May 1, 1990): 2223–29. http://dx.doi.org/10.1152/jappl.1990.68.5.2223.
Повний текст джерелаАнотація:
In normal humans and dogs, the airways do not constrict to closure even when maximally stimulated. However, airway closure can be produced in isolated canine lobes and bronchial segments that are stimulated with maximal concentrations of bronchoconstrictors. These observations suggest that under normal conditions, physiological mechanisms to limit bronchoconstriction exist in vivo. In this investigation, we evaluated how mechanical factors that influence airway smooth muscle contractility contribute to the modulation of the pressure-volume characteristics of contracted canine intraparenchymal airways in vitro. Our results demonstrated that maximal and even submaximal contractile stimuli can produce airway closure in bronchi that are allowed to contract under isobaric conditions. However, the effectiveness of bronchoconstrictors is significantly reduced when the airways are subjected to tidal volume oscillations during contraction. In addition, airways contracted isovolumetrically at low volumes exhibit a markedly reduced sensitivity to submaximal concentrations of acetylcholine. This may limit bronchoconstriction at low lung volumes and transpulmonary pressures where the effectiveness of parenchymal stress in keeping the airways open is reduced. Together these factors could provide a mechanism by which bronchoconstriction is limited to low levels of airway resistance under normal conditions in vivo.
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Barnett, William H., Elizaveta M. Latash, Robert A. Capps, Thomas E. Dick, Erica A. Wehrwein, and Yaroslav I. Molkov. "Traube–Hering waves are formed by interaction of respiratory sinus arrhythmia and pulse pressure modulation in healthy men." Journal of Applied Physiology 129, no. 5 (November 1, 2020): 1193–202. http://dx.doi.org/10.1152/japplphysiol.00452.2020.
Повний текст джерелаАнотація:
Variability in blood pressure has become an important metric to consider as more is learned about the link between excessive blood pressure variability and adverse health outcomes. In this study using slow deep breathing in human subjects, we found that heart rate and pulse pressure variations have comparable effects on the amplitude of blood pressure waves, and it is the common action of the two that defines the phase relationship between respiration and blood pressure oscillations.
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Wei, Ning, and Anita T. Layton. "Theoretical assessment of the Ca2+ oscillations in the afferent arteriole smooth muscle cell of the rat kidney." International Journal of Biomathematics 11, no. 03 (April 2018): 1850043. http://dx.doi.org/10.1142/s1793524518500432.
Повний текст джерелаАнотація:
The afferent arteriole (AA) of rat kidney exhibits the myogenic response, in which the vessel constricts in response to an elevation in blood pressure and dilates in response to a pressure reduction. Additionally, the AA exhibits spontaneous oscillations in vascular tone at physiological luminal pressures. These time-periodic oscillations stem from the dynamic exchange of Ca[Formula: see text] between the cytosol and the sarcoplasmic reticulum, coupled to the stimulation of Ca[Formula: see text]-activated potassium and chloride channels, and to the modulation of voltage-gated L-type Ca[Formula: see text] channels. The effects of physiological factors, including blood pressure and vasoactive substances, on AA vasomotion remain to be well characterized. In this paper, we analyze a mathematical model of Ca[Formula: see text] signaling in an AA smooth muscle cell. The model represents detailed transmembrane ionic transport, intracellular Ca[Formula: see text] dynamics as well as kinetics of nitric oxide (NO) and superoxide (O[Formula: see text]) formation, diffusion and reaction. NO is an important factor in the maintenance of blood pressure and O[Formula: see text] has been shown to contribute significantly to the functional alternations of blood vessels in hypertension. We perform a bifurcation analysis of the model equations to assess the effect of luminal pressure, NO and O[Formula: see text] on the behaviors of limit cycle oscillations.
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Le Ray, Didier, Frédéric Brocard, and Réjean Dubuc. "Muscarinic Modulation of the Trigemino-Reticular Pathway in Lampreys." Journal of Neurophysiology 92, no. 2 (August 2004): 926–38. http://dx.doi.org/10.1152/jn.01025.2003.
Повний текст джерелаАнотація:
In lampreys, reticulospinal neurons integrate sensory inputs to adapt their control onto the spinal locomotor networks. Whether and how sensory inputs to reticulospinal neurons are modulated remains to be determined. We showed recently that cholinergic inputs onto reticulospinal neurons play a key role in the initiation of locomotion elicited by stimulation of the mesencephalic locomotor region in semi intact lampreys. Here, we examined the possible role of muscarinic acetylcholine receptors in modulating trigeminal inputs to reticulospinal neurons. A local application of muscarinic agonists onto an intracellularly recorded reticulospinal cell depressed the disynaptic responses to trigeminal stimulation. A depression was also observed when muscarinic agonists were pressure ejected over the brain stem region containing second-order neurons relaying trigeminal inputs to reticulospinal neurons. Conversely, muscarinic antagonists increased the trigeminal-evoked responses, suggesting that a muscarinic depression of sensory inputs to RS neurons is exerted tonically. The muscarinic modulation affected predominantly the N-methyl-d-aspartate (NMDA) component of the trigeminal-evoked responses. Moreover, atropine perfusion facilitated the occurrence of sustained depolarizations induced by stimulation of the trigeminal nerve, and it revealed NMDA-induced intrinsic oscillations in reticulospinal neurons. The functional significance of a muscarinic modulation of a sensory transmission to reticulospinal neurons is discussed.
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Kahr, Matthias, Michael Stifter, Harald Steiner, Wilfried Hortschitz, Gabor Kovács, Andreas Kainz, Johannes Schalko, and Franz Keplinger. "Dual Resonator MEMS Magnetic Field Gradiometer." Sensors 19, no. 3 (January 25, 2019): 493. http://dx.doi.org/10.3390/s19030493.
Повний текст джерелаАнотація:
Accurate knowledge of the spatial magnetic field distribution is necessary when measuring field gradients. Therefore, a MEMS magnetic field gradiometer is reported, consisting of two identical, but independent laterally oscillating masses on a single chip. The sensor is actuated by Lorentz force and read out by modulation of the light flux passing through stationary and moving arrays of the chip. This optical readout decouples the transducer from the electronic components. Both phase and intensity are recorded which reveals information about the uniformity of the magnetic field. The magnetic flux density is measured simultaneously at two points in space and the field gradient is evaluated locally. The sensor was characterised at ambient pressure by performing frequency and magnitude response measurements with coil and various different permanent magnet arrangements, resulting in a responsivity of 35.67 V/T and detection limit of 3.07 µT/ Hz (@ 83 Hz ENBW). The sensor is compact, offers a large dynamic measurement range and can be of low-cost by using conventional MEMS batch fabrication technology.
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Zhang, Qingxin, Hooman Homayouni, Byron D. Gates, Michael H. Eikerling, and Amir M. Niroumand. "Electrochemical Pressure Impedance Spectroscopy for Polymer Electrolyte Fuel Cells via Back-Pressure Control." Journal of The Electrochemical Society 169, no. 4 (April 1, 2022): 044510. http://dx.doi.org/10.1149/1945-7111/ac6326.
Повний текст джерелаАнотація:
Electrochemical pressure impedance spectroscopy (EPIS) analyses the voltage response of a polymer electrolyte fuel cell (PEFC) as a function of an applied pressure signal in the frequency domain. EPIS is similar to electrochemical impedance spectroscopy (EIS) and its development was inspired by the diagnostic capabilities of the latter. The EPIS introduced in this work modulates the cathode pressure of a PEFC with a sinusoidal signal through the use of a back-pressure controller, and monitors the cell voltage while holding the cell at a constant current. A sinusoidal pressure wave propagates along the flow field channels because of this pressure modulation. This pressure wave impacts local reaction rates and transport properties in the cathode, resulting in a sinusoidal voltage response. The amplitude ratio and phase difference between these two sinusoidal waves entail diagnostic information on processes that take place within the PEFC. To demonstrate the utility of the EPIS technique, experiments have been carried out to measure and analyze the frequency response of PEFCs with two different flow fields. A parametric study has been conducted to characterize the effect of pressure oscillation amplitude, load, oxygen concentration, oxygen stoichiometry and cathode gas flow rate on the EPIS signal.
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Meijlink, Bram, Ines Beekers, Simone A. G. Langeveld, Kristina Bishard, Antonius F. van der Steen, Nico de Jong, Sebastiaan J. Trietsch, and Klazina Kooiman. "The OrganoPlate® as vessel-on-a-chip model to investigate increased microbubble-mediated vascular permeability." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A174. http://dx.doi.org/10.1121/10.0011016.
Повний текст джерелаАнотація:
The vessel wall is an important barrier modulating drug delivery to the underlying diseased tissue. Oscillating microbubbles can be used to locally enhance vascular permeability and sonoporate cells. As the mechanism is not fully understood, our aim was to grow 3D human vessels-on-a-chip in the OrganoPlate® 40 and use this model to investigate the effect of αvβ3 -targeted microbubble and different ultrasound pressures (2 MHz, 100–850 kPa peak negative pressure) and cycle lengths (10×10 or 10×1000 cycles) on vascular permeability and sonoporation. The vascular permeability of 122 microvessels in 14 different conditions was quantified by microscopy imaging using the leakage pattern of a 150 kDa FITC-dextran dye. Furthermore, sonoporation was assessed using propidium iodide (PI). Upon microbubble and ultrasound treatment, an increase in vascular permeability was observed. Higher pressures and longer cycle length treatment showed a significantly higher vascular permeability and significant increase in PI uptake compared to all control groups (sham, ultrasound only, microbubble only), suggesting a simultaneous increase in vascular permeability and sonoporation correlating with higher pressure and longer cycle insonifications. In conclusion, the vessel-on-chip model is a suitable model to investigate how insonification with different ultrasound settings affects the microbubble-mediated vascular permeability increase and sonoporation.
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Warner, M. R., and J. M. Loeb. "Beat-by-beat modulation of AV conduction. I. Heart rate and respiratory influences." American Journal of Physiology-Heart and Circulatory Physiology 251, no. 6 (December 1, 1986): H1126—H1133. http://dx.doi.org/10.1152/ajpheart.1986.251.6.h1126.
Повний текст джерелаАнотація:
We examined the integration of heart rate and neural influences at the atrioventricular (AV) node in conscious dogs. Animals were anesthetized and, under sterile conditions, instrumented to chronically record atrial and ventricular electrograms and blood pressure. In the conscious state, electrocardiogram (ECG), respiration, blood pressure, and electrograms were recorded on a beat-by-beat basis, and heart rate and AV interval were plotted graphically as a function of time. Resting animals exhibited both respiratory sinus arrhythmia and marked oscillations in AV conduction time associated with respiration. During inspiration AV interval was shortened, and during expiration AV interval was prolonged. To obviate the effect of cyclic changes in heart rate, atrial pacing was used to increase heart rate over a wide range both abruptly and linearly. Regardless of the pattern of heart rate change, AV interval oscillated at the respiratory frequency at pacing rates 10-100 beats/min above control. Higher levels of atrial pacing resulted in AV conduction patterns that were correlated with changes in blood pressure. Thus in the conscious dog variations in AV conduction time occur on a beat-by-beat basis in conjunction with respiration; oscillatory activity of AV conduction is not dependent on simultaneous changes in heart rate; and during atrial pacing, autonomic neural activity associated with respiration and blood pressure appears to dynamically modulate AV conduction with respiratory effects predominating at low heart rates and blood pressure effects at high heart rates.
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Hood, Lon L., Malori A. Redman, Wes L. Johnson, and Thomas J. Galarneau. "Stratospheric Influences on the MJO-Induced Rossby Wave Train: Effects on Intraseasonal Climate." Journal of Climate 33, no. 1 (January 1, 2020): 365–89. http://dx.doi.org/10.1175/jcli-d-18-0811.1.
Повний текст джерелаАнотація:
AbstractThe tropical Madden–Julian oscillation (MJO) excites a northward propagating Rossby wave train that largely determines the extratropical surface weather consequences of the MJO. Previous work has demonstrated a significant influence of the tropospheric El Niño–Southern Oscillation (ENSO) on the characteristics of this wave train. Here, composite analyses of ERA-Interim sea level pressure (SLP) and surface air temperature (SAT) data during the extended northern winter season are performed to investigate the additional role of stratospheric forcings [the quasi-biennial oscillation (QBO) and the 11-yr solar cycle] in modifying the wave train and its consequences. MJO phase composites of 20–100-day filtered data for the two QBO phases show that, similar to the cool phase of ENSO, the easterly phase of the QBO (QBOE) produces a stronger wave train and associated modulation of SLP and SAT anomalies. In particular, during MJO phases 5–7, positive SLP and negative SAT anomalies in the North Atlantic/Eurasian sector are enhanced during QBOE relative to the westerly phase of the QBO (QBOW). The opposite occurs during the earliest MJO phases. SAT anomalies over eastern North America are also more strongly modulated during QBOE. Although less certain because of the short data record, there is some evidence that the minimum phase of the solar cycle (SMIN) produces a similar increased modulation of SLP and SAT anomalies. The strongest modulations of SLP and SAT anomalies are produced when two or more of the forcings are superposed (e.g., QBOE/cool ENSO, SMIN/QBOE, etc.).
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Delgado, Esmeralda Sofia Costa, Carlos Marques-Neves, Maria Isabel Sousa Rocha, José Paulo Pacheco Sales-Luís, and Luís Filipe Silva-Carvalho. "Modulation of Vasomotive Activity in Rabbit External Ophthalmic Artery by Neuropeptides." Journal of Ophthalmology 2012 (2012): 1–6. http://dx.doi.org/10.1155/2012/498565.
Повний текст джерелаАнотація:
Purpose. To investigate the vasomotive activity upon the external ophthalmic artery of vasointestinal peptide (VIP) and neuropeptide Y (NPY) using a previously developed model.Methods. Isolated rabbit eyes (n=12) were perfusedin situwith tyrode through the external ophthalmic artery. Effects of intra-arterial injections of NPY 200 μg/ml (Group A;n=6) and VIP 200 μg/ml (Group B;n=6) on the recorded pressure were obtained. For statistical analysis, Student's pairedt-test and Fast Fourier Transform were used.Results. Spontaneous oscillations were observed before any drug administration in the 12 rabbit models. NPY produced an increase in total vascular resistance and a higher frequency and amplitude of oscillations, while VIP evoked the opposite effects.Conclusions. This study provides evidence of vasomotion in basal conditions in rabbit external ophthalmic artery. Concerning drug effects, NPY increased arterial resistance and enhanced vasomotion while VIP produced opposite effects which demonstrates their profound influence in arterial vasomotion.
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Arregui, Guillermo, Martín F. Colombano, Jeremie Maire, Alessandro Pitanti, Néstor E. Capuj, Amadeu Griol, Alejandro Martínez, Clivia M. Sotomayor-Torres, and Daniel Navarro-Urrios. "Injection locking in an optomechanical coherent phonon source." Nanophotonics 10, no. 4 (January 1, 2021): 1319–27. http://dx.doi.org/10.1515/nanoph-2020-0592.
Повний текст джерелаАнотація:
Abstract Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.
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Stenkamp, Kerstin, J. Matias Palva, Marylka Uusisaari, Sebastian Schuchmann, Dietmar Schmitz, Uwe Heinemann, and Kai Kaila. "Enhanced Temporal Stability of Cholinergic Hippocampal Gamma Oscillations Following Respiratory Alkalosis In Vitro." Journal of Neurophysiology 85, no. 5 (May 1, 2001): 2063–69. http://dx.doi.org/10.1152/jn.2001.85.5.2063.
Повний текст джерелаАнотація:
The decrease in brain CO2 partial pressure (pCO2) that takes place both during voluntary and during pathological hyperventilation is known to induce gross alterations in cortical functions that lead to subjective sensations and altered states of consciousness. The mechanisms that mediate the effects of the decrease in pCO2 at the neuronal network level are largely unexplored. In the present work, the modulation of gamma oscillations by hypocapnia was studied in rat hippocampal slices. Field potential oscillations were induced by the cholinergic agonist carbachol under an N-methyl-D-aspartate (NMDA)-receptor blockade and were recorded in the dendritic layer of the CA3 region with parallel measurements of changes in interstitial and intraneuronal pH (pHo and pHi, respectively). Hypocapnia from 5 to 1% CO2 led to a stable monophasic increase of 0.5 and 0.2 units in pHo and pHi, respectively. The mean oscillation frequency increased slightly but significantly from 32 to 34 Hz and the mean gamma-band amplitude (20 to 80 Hz) decreased by 20%. Hypocapnia induced a dramatic enhancement of the temporal stability of the oscillations, as was indicated by a two-fold increase in the exponential decay time constant fitted to the autocorrelogram. A rise in pHi evoked by the weak base trimethylamine (TriMA) was associated with a slight increase in oscillation frequency (37 to 39 Hz) and a decrease in amplitude (30%). Temporal stability, on the other hand, was decreased by TriMA, which suggests that its enhancement in 1% CO2 was related to the rise in pHo. In 1% CO2, the decay-time constant of the evoked monosynaptic pyramidal inhibitory postsynaptic current (IPSC) was unaltered but its amplitude was enhanced. This increase in IPSC amplitude seems to significantly contribute to the enhancement of temporal stability because the enhancement was almost fully reversed by a low concentration of bicuculline. These results suggest that changes in brain pCO2 can have a strong influence on the temporal modulation of gamma rhythms.
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Schilden, Thomas, and Wolfgang Schröder. "Inclined slow acoustic waves incident to stagnation point probes in supersonic flow." Journal of Fluid Mechanics 866 (March 13, 2019): 567–97. http://dx.doi.org/10.1017/jfm.2019.121.
Повний текст джерелаАнотація:
Tunnel noise in supersonic testing facilities is known to be a decisive factor in boundary layer transition experiments. It defines initial conditions for the growth of modal instabilities by the receptivity mechanism. That is, to interpret experimental results, the determination of tunnel noise is of crucial importance. It is common to use stagnation point probes equipped with pressure transducers in supersonic flows, but since tunnel noise undergoes modulation during the measurement, the probes must be calibrated. The predominant component of tunnel noise is caused by the nozzle boundary layer which radiates highly inclined slow acoustic waves. Therefore, the calibration of stagnation point probes for these disturbances is essential. For quasi-steady deviations from the free stream, an analytic reduced-order method holds. A corresponding conflicting model derived by Stainback & Wagner (1972, AIAA Paper 72-1003) is revised and corrected. Inclined slow acoustic waves generate higher pressure perturbations at the probe than non-inclined waves. In general, costly three-dimensional direct numerical simulations can be used for calibration. In this study, however, new axisymmetric boundary conditions are proposed to reduce the problem to two dimensions to efficiently investigate the detection of incident inclined slow acoustic waves by stagnation point probes. A cylindrical probe with a rounded edge is investigated in supersonic flow at a Mach number $Ma=5.9$. For the inclination angle of radiated slow acoustic waves, stagnation point pressure fluctuations abruptly decay with increasing Strouhal number and a similar behaviour can be seen at constant Strouhal number with increasing inclination angle. Two simple criteria for the onset of decay based on the radial wavenumber are deduced. Furthermore, stagnation point pressure fluctuations were decomposed into an initial pulse impact and resonant amplification to separately investigate the effects. The initial pulse determines the overall pressure signal. At high inclination angles, a new mechanism for resonance caused by a surface pressure wave travelling at the phase speed of the incident wave was found to supersede resonance caused by oscillating acoustic waves prevailing at low inclination angles.
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Morris, K. F., S. C. Nuding, L. S. Segers, D. M. Baekey, R. Shannon, B. G. Lindsey, and T. E. Dick. "Respiratory and Mayer wave-related discharge patterns of raphé and pontine neurons change with vagotomy." Journal of Applied Physiology 109, no. 1 (July 2010): 189–202. http://dx.doi.org/10.1152/japplphysiol.01324.2009.
Повний текст джерелаАнотація:
Previous models have attributed changes in respiratory modulation of pontine neurons after vagotomy to a loss of pulmonary stretch receptor “gating” of an efference copy of inspiratory drive. Recently, our group confirmed that pontine neurons change firing patterns and become more respiratory modulated after vagotomy, although average peak and mean firing rates of the sample did not increase (Dick et al., J Physiol 586: 4265–4282, 2008). Because raphé neurons are also elements of the brain stem respiratory network, we tested the hypotheses that after vagotomy raphé neurons have increased respiratory modulation and that alterations in their firing patterns are similar to those seen for pontine neurons during withheld lung inflation. Raphé and pontine neurons were recorded simultaneously before and after vagotomy in decerebrated cats. Before vagotomy, 14% of 95 raphé neurons had increased activity during single respiratory cycles prolonged by withholding lung inflation; 13% exhibited decreased activity. After vagotomy, the average index of respiratory modulation (η2) increased (0.05 ± 0.10 to 0.12 ± 0.18 SD; Student's paired t-test, P < 0.01). Time series and frequency domain analyses identified pontine and raphé neuron firing rate modulations with a 0.1-Hz rhythm coherent with blood pressure Mayer waves. These “Mayer wave-related oscillations” (MWROs) were coupled with central respiratory drive and became synchronized with the central respiratory rhythm after vagotomy (7 of 10 animals). Cross-correlation analysis identified functional connectivity in 52 of 360 pairs of neurons with MWROs. Collectively, the results suggest that a distributed network participates in the generation of MWROs and in the coordination of respiratory and vasomotor rhythms.
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Cerutti, C., C. Barres, and C. Paultre. "Baroreflex modulation of blood pressure and heart rate variabilities in rats: assessment by spectral analysis." American Journal of Physiology-Heart and Circulatory Physiology 266, no. 5 (May 1, 1994): H1993—H2000. http://dx.doi.org/10.1152/ajpheart.1994.266.5.h1993.
Повний текст джерелаАнотація:
The role of the baroreflex in the spectral characteristics of mean arterial pressure (MAP) and heart rate (HR) was investigated in 12 control rats and 9 rats with chronic sinoaortic baroreceptor denervation (SAD) during 1) basal conditions and 2) ganglionic blockade with chlorisondamine and restoration of the basal MAP level. In SAD rats, power spectral density of MAP, estimated by a fast Fourier transform, was reduced in the low-frequency (LF, 0.27- to 0.74-Hz) band. Ganglionic blockade highly decreased LF power spectral density of MAP in control rats. No relationship was found between the MAP response to chlorisondamine, taken as an index of the sympathetic vasomotor tone, and the basal LF power spectral density. Transfer function analysis between MAP and HR showed that, in control rats, coherence was high for frequencies surrounding the LF and high-frequency peaks. In SAD rats, coherence was abolished in the LF band but maintained in the high-frequency band. In conclusion, approximately 80% of the LF power spectral density of MAP depends on the sympathetic nervous system activity, and the baroreflex accounts for one-half of this power and for the coherence between MAP and HR oscillations in the LF band.
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Fazan, Rubens, Mauro de Oliveira, Valdo José Dias da Silva, Luis Fernando Joaquim, Nicola Montano, Alberto Porta, Mark W. Chapleau, and Helio C. Salgado. "Frequency-dependent baroreflex modulation of blood pressure and heart rate variability in conscious mice." American Journal of Physiology-Heart and Circulatory Physiology 289, no. 5 (November 2005): H1968—H1975. http://dx.doi.org/10.1152/ajpheart.01224.2004.
Повний текст джерелаАнотація:
The goal of this study was to determine the baroreflex influence on systolic arterial pressure (SAP) and pulse interval (PI) variability in conscious mice. SAP and PI were measured in C57Bl/6J mice subjected to sinoaortic deafferentation (SAD, n = 21) or sham surgery ( n = 20). Average SAP and PI did not differ in SAD or control mice. In contrast, SAP variance was enhanced (21 ± 4 vs. 9.5 ± 1 mmHg2) and PI variance reduced (8.8 ± 2 vs. 26 ± 6 ms2) in SAD vs. control mice. High-frequency (HF: 1–5 Hz) SAP variability quantified by spectral analysis was greater in SAD (8.5 ± 2.0 mmHg2) compared with control (2.5 ± 0.2 mmHg2) mice, whereas low-frequency (LF: 0.1–1 Hz) SAP variability did not differ between the groups. Conversely, LF PI variability was markedly reduced in SAD mice (0.5 ± 0.1 vs. 10.8 ± 3.4 ms2). LF oscillations in SAP and PI were coherent in control mice (coherence = 0.68 ± 0.05), with changes in SAP leading changes in PI (phase = −1.41 ± 0.06 radians), but were not coherent in SAD mice (coherence = 0.08 ± 0.03). Blockade of parasympathetic drive with atropine decreased average PI, PI variance, and LF and HF PI variability in control ( n = 10) but had no effect in SAD ( n = 6) mice. In control mice, blockade of sympathetic cardiac receptors with propranolol increased average PI and decreased PI variance and LF PI variability ( n = 6). In SAD mice, propranolol increased average PI ( n = 6). In conclusion, baroreflex modulation of PI contributes to LF, but not HF PI variability, and is mediated by both sympathetic and parasympathetic drives in conscious mice.
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Minerick, Adrienne Robyn, Hsueh-Chia Chang, Todd M. Hoagland, and Kenneth R. Olson. "Dynamic synchronization analysis of venous pressure-driven cardiac output in rainbow trout." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, no. 4 (October 2003): R889—R896. http://dx.doi.org/10.1152/ajpregu.00228.2003.
Повний текст джерелаАнотація:
Measurement of venous function in vivo is inherently difficult. In this study, we used the Hilbert transform to examine the dynamic relationships between venous pressure and cardiac output (CO) in rainbow trout whose blood volume was continuously increased and decreased by ramp infusion and withdrawal (I/W). The dorsal aorta and ductus Cuvier were cannulated percutaneously and connected to pressure transducers; a flow probe was placed around the ventral aorta. Whole blood from a donor was then I/W via the dorsal aortic cannula at a rate of 10% of the estimated blood volume per minute, and the duration of I/W was varied from 40, 60, 80, 90, 120, 230, 240, 260, 300, and 340 s. Compliance [change in (Δ) blood vol/Δvenous pressure] was 2.8 ± 0.2 ml · mmHg-1 · g-1 ( N = 25 measurements; 6 fish with closed pericardium) and 2.8 ± 0.3 ml · mmHg-1 · kg-1 ( N = 19 measurements, 4 fish with open pericardium). Compliance was positively correlated with the duration of I/W, indicative of cardiovascular reflex responses at longer I/W durations. In trout with closed pericardium, CO followed venous pressure oscillations with an average time lag of 4.2 ± 1.0 s ( N = 9); heart rate (HR) was inversely correlated with CO. These studies show that CO is entrained by modulation of venous pressure, not by HR. Thus, although trout have a rigid pericardium, venous pressure (vis-a-tergo), not cardiac suction (vis-a-fronte), appears to be the primary determinant of CO. Estimation of venous compliance by ramp-modulation of venous pressure is faster and less traumatic than classical capacitance measurements and appears applicable to a variety of vertebrate species, as does the Hilbert transform, which permits analysis of signals with disparate frequencies.
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Schrøder, T. M., and D. Rosbjerg. "Groundwater recharge and capillary rise in a clayey catchment: modulation by topography and the Arctic Oscillation." Hydrology and Earth System Sciences 8, no. 6 (December 31, 2004): 1090–102. http://dx.doi.org/10.5194/hess-8-1090-2004.
Повний текст джерелаАнотація:
Abstract. The signature left by capillary rise in the water balance is investigated for a 16 km2 clayey till catchment in Denmark. Integrated modelling for 1981–99 substantiates a 30% uphill increase in average net recharge, caused by the reduction in capillary rise when the water table declines. Calibration of the groundwater module is constrained by stream flow separation and water table wells. Net recharge and a priori parameterisation has been estimated from those same data, an automatic rain gauge and electrical sounding. Evaluation of snow storage and compensation for a simplified formulation of unsaturated hydraulic conductivity contribute to a modelling of the precipitation-runoff relation that compares well with measurements in other underdrained clayey catchments. The capillary rise is assumed to be responsible for a 30% correlation between annual evapotranspiration and the North Atlantic Oscillation. The observed correlation, and the hypothesis of a hemispherical Arctic Oscillation linking atmospheric pressure with surface temperature, suggests that modelled evapotranspiration from clayey areas is better than precipitation records for identifying the region influenced by oscillation. Keywords: catchment modelling, MIKE SHE, capillary rise, degree-day model, climate
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Leung, Richard S. T., John S. Floras, and T. Douglas Bradley. "Respiratory modulation of the autonomic nervous system during Cheyne–Stokes respirationThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigator's Forum." Canadian Journal of Physiology and Pharmacology 84, no. 1 (January 2006): 61–66. http://dx.doi.org/10.1139/y05-145.
Повний текст джерелаАнотація:
Cheyne–Stokes respiration (CSR) is associated with increased mortality among patients with heart failure. However, the specific link between CSR and mortality remains unclear. One possibility is that CSR results in excitation of the sympathetic nervous system. This review relates evidence that CSR exerts acute effects on the autonomic nervous system during sleep, and thereby influences a number of cardiovascular phenomena, including heart rate, blood pressure, atrioventricular conduction, and ventricular ectopy. In patients in sinus rhythm, heart rate and blood pressure oscillate during CSR in association with respiratory oscillations, such that both peak heart rate and blood pressure occur during the hyperpneic phase. Inhalation of CO2 abolishes both CSR and the associated oscillations in heart rate and blood pressure. In contrast, O2 inhalation sufficient to eliminate hypoxic dips has no significant effect on CSR, heart rate, or blood pressure. In patients with atrial fibrillation, ventricular rate oscillates in association with CSR despite the absence of within-breath respiratory arrhythmia. The comparison of RR intervals between the apneic and hyperpneic phases of CSR indicates that this breathing disorder exerts its effect on ventricular rate by inducing cyclical changes in atrioventricular node conduction properties. In patients with frequent ventricular premature beats (VPBs), VPBs occur more frequently during the hyperpneic phase than the apneic phase of CSR. VPB frequency is also higher during periods of CSR than during periods of regular breathing, with or without correction of hypoxia. In summary, CSR exerts multiple effects on the cardiovascular system that are likely manifestations of respiratory modulation of autonomic activity. It is speculated that the rhythmic oscillations in autonomic tone brought about by CSR may ultimately contribute to the sympatho-excitation and increased mortality long observed in patients with heart failure and CSR.
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LaPrad, Adam S., Thomas L. Szabo, Béla Suki, and Kenneth R. Lutchen. "Tidal stretches do not modulate responsiveness of intact airways in vitro." Journal of Applied Physiology 109, no. 2 (August 2010): 295–304. http://dx.doi.org/10.1152/japplphysiol.00107.2010.
Повний текст джерелаАнотація:
Studies on isolated tracheal airway smooth muscle (ASM) strips have shown that length/force fluctuations, similar to those likely occurring during breathing, will mitigate ASM contractility. These studies conjecture that, solely by reducing length oscillations on a healthy, intact airway, one can create airway hyperresponsiveness, but this has never been explicitly tested. The intact airway has additional complexities of geometry and structure that may impact its relevance to isolated ASM strips. We examined the role of transmural pressure (Ptm) fluctuations of physiological amplitudes on the responsiveness of an intact airway. We developed an integrated system utilizing ultrasound imaging to provide real-time measurements of luminal radius and wall thickness over the full length of an intact airway ( generation 10 and below) during Ptm oscillations. First, airway constriction dynamics to cumulative acetylcholine (ACh) doses (10−7 to 10−3 M) were measured during static and dynamic Ptm protocols. Regardless of the breathing pattern, the Ptm oscillation protocols were ineffective in reducing the net level of constriction for any ACh dose, compared with the static control ( P = 0.225–0.793). Next, Ptm oscillations of increasing peak-to-peak amplitude were applied subsequent to constricting intact airways under static conditions (5.0-cmH2O Ptm) with a moderate ACh dose (10−5 M). Peak-to-peak Ptm oscillations ≤5.0 cmH2O resulted in no statistically significant bronchodilatory response ( P = 0.429 and 0.490). Larger oscillations (10 cmH2O, peak to peak) produced modest dilation of 4.3% ( P = 0.009). The lack of modulation of airway responsiveness by Ptm oscillations in intact, healthy airways suggests that ASM level mechanisms alone may not be the sole determinant of airway responsiveness.
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Barrett, Bradford S., Jorge F. Carrasco, and Anthony P. Testino. "Madden–Julian Oscillation (MJO) Modulation of Atmospheric Circulation and Chilean Winter Precipitation." Journal of Climate 25, no. 5 (March 2012): 1678–88. http://dx.doi.org/10.1175/jcli-d-11-00216.1.
Повний текст джерелаАнотація:
The leading intraseasonal mode of tropical atmospheric variability, the Madden–Julian oscillation (MJO), has been shown to modulate precipitation and circulation on a global and regional scale. Winter precipitation in Chile has been connected to a variety of synoptic-scale forcing mechanisms. This study explored the links between the two, first examining the intraseasonal variability of Chilean precipitation from surface gauges and the Tropical Rainfall Measuring Mission (TRMM) and then examining the variability of synoptic-scale circulation. Composites of precipitation, precipitation intensity, and lower-, middle-, and upper-tropospheric circulation were created using the Real-Time Multivariate MJO index, which divides the MJO into eight longitudinally based phases. Precipitation was found to vary across MJO phases, with positive precipitation anomalies in central and south-central Chile (30°–45°S) for MJO phases 8, 1, and 2, and negative anomalies in phases 3–7. Circulation was also found to vary across phase, in good agreement with precipitation: low geopotential height and negative omega (corresponding to upward vertical motion) anomalies were found over and upstream of Chile during the rainier phases, and the anomalies reversed during the drier phases. Surface pressure and middle- and upper-tropospheric geopotential height anomalies showed a classic equivalent barotropic wave train, indicating a teleconnection response to deep convective activity in the Maritime Continent in agreement with numerous earlier observational, modeling, and theoretical studies.
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Hassa, C., J. Heinze, and K. Stursberg. "Investigation of the Response of an Air Blast Atomizer Combustion Chamber Configuration on Forced Modulation of Air Feed at Realistic Operating Conditions." Journal of Engineering for Gas Turbines and Power 125, no. 4 (October 1, 2003): 872–78. http://dx.doi.org/10.1115/1.1584478.
Повний текст джерелаАнотація:
DLR investigated forced combustion oscillations of two liquid fuel burners in a research combustion chamber at elevated pressures simulating idle conditions of aircraft engine combustors. The work was performed in collaboration with MTU Munich. An existing combustion chamber with optical access, capable to operate up to 20 bar, was upgraded with an air flow pulsator, that bypasses air from the combustor plenum to the exhaust with a sinusoidal massflow variation up to 700 Hz. Pressure transducers in the plenum and the flame tube monitored the forced disturbances. A photomultiplier recorded the OH* chemiluminescence of the flame. For the agreed operating conditions frequency scans of these values were registered. Additionally images of the OH* chemiluminescence were taken at selected frequencies and evaluated in a statistical manner, to separate turbulent and periodic behavior. From the analysis of the pressure data, it can be concluded, that serious thermoacoustic feedback was not observed for both burners. However, burner 2 with the flame detached from the wall exhibited a higher fluctuation level as burner 1 with the wall attached flame. A resonant behavior was observed near the characteristic frequency of the sound room comprised of plenum, flame tube, and burner nozzle as connecting passage. The chemiluminescence images show different modes of spatial fluctuation for the burners and for burner 2 they also vary with the operating condition.
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Edwards, Aurélie, and Anita T. Layton. "Calcium dynamics underlying the myogenic response of the renal afferent arteriole." American Journal of Physiology-Renal Physiology 306, no. 1 (January 1, 2014): F34—F48. http://dx.doi.org/10.1152/ajprenal.00317.2013.
Повний текст джерелаАнотація:
The renal afferent arteriole reacts to an elevation in blood pressure with an increase in muscle tone and a decrease in luminal diameter. This effect, known as the myogenic response, is believed to stabilize glomerular filtration and to protect the glomerulus from systolic blood pressure increases, especially in hypertension. To study the mechanisms underlying the myogenic response, we developed a mathematical model of intracellular Ca2+ signaling in an afferent arteriole smooth muscle cell. The model represents detailed transmembrane ionic transport, intracellular Ca2+ dynamics, the kinetics of myosin light chain phosphorylation, and the mechanical behavior of the cell. It assumes that the myogenic response is initiated by pressure-induced changes in the activity of nonselective cation channels. Our model predicts spontaneous vasomotion at physiological luminal pressures and KCl- and diltiazem-induced diameter changes comparable to experimental findings. The time-periodic oscillations stem from the dynamic exchange of Ca2+ between the cytosol and the sarcoplasmic reticulum, coupled to the stimulation of Ca2+-activated potassium (KCa) and chloride (ClCa) channels, and the modulation of voltage-activated L-type channels; blocking sarco/endoplasmic reticulum Ca2+ pumps, ryanodine receptors (RyR), KCa, ClCa, or L-type channels abolishes these oscillations. Our results indicate that the profile of the myogenic response is also strongly dependent on the conductance of ClCa and L-type channels, as well as the activity of plasmalemmal Ca2+ pumps. Furthermore, inhibition of KCa is not necessary to induce myogenic contraction. Lastly, our model suggests that the kinetic behavior of L-type channels results in myogenic kinetics that are substantially faster during constriction than during dilation, consistent with in vitro observations (Loutzenhiser R, Bidani A, Chilton L. Circ. Res. 90: 1316–1324, 2002).
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Sosnovtseva, Olga V., Alexey N. Pavlov, Erik Mosekilde, Kay-Pong Yip, Niels-Henrik Holstein-Rathlou, and Donald J. Marsh. "Synchronization among mechanisms of renal autoregulation is reduced in hypertensive rats." American Journal of Physiology-Renal Physiology 293, no. 5 (November 2007): F1545—F1555. http://dx.doi.org/10.1152/ajprenal.00054.2007.
Повний текст джерелаАнотація:
We searched for synchronization among autoregulation mechanisms using wavelet transforms applied to tubular pressure recordings in nephron pairs from the surface of rat kidneys. Nephrons have two oscillatory modes in the regulation of their pressures and flows: a faster (100–200 mHz) myogenic mode, and a slower (20–40 mHz) oscillation in tubuloglomerular feedback (TGF). These mechanisms interact; the TGF mode modulates both the amplitude and the frequency of the myogenic mode. Nephrons also communicate with each other using vascular signals triggered by membrane events in arteriolar smooth muscle cells. In addition, the TGF oscillation changes in hypertension to an irregular fluctuation with characteristics of deterministic chaos. The analysis shows that, within single nephrons of normotensive rats, the myogenic mode and TGF are synchronized at discrete frequency ratios, with 5:1 most common. There is no distinct synchronization ratio in spontaneously hypertensive rats (SHR). In normotensive rats, full synchronization of both TGF and myogenic modes is the most probable state for pairs of nephrons originating in a common cortical radial artery. For SHR, full synchronization is less probable; most common in SHR is a state of partial synchronization with entrainment between neighboring nephrons for only one of the modes. Modulation of the myogenic mode by the TGF mode is much stronger in hypertensive than in normotensive rats. Synchronization among nephrons forms the basis for an integrated reaction to blood pressure fluctuations. Reduced synchronization in SHR suggests that the effectiveness of the coordinated response is impaired in hypertension.
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Tanaka, Yuki, Ichiro Yasuda, Hiroyasu Hasumi, Hiroaki Tatebe, and Satoshi Osafune. "Effects of the 18.6-yr Modulation of Tidal Mixing on the North Pacific Bidecadal Climate Variability in a Coupled Climate Model." Journal of Climate 25, no. 21 (November 2012): 7625–42. http://dx.doi.org/10.1175/jcli-d-12-00051.1.
Повний текст джерелаАнотація:
Diapycnal mixing induced by tide–topography interaction, one of the essential factors maintaining the global ocean circulation and hence the global climate, is modulated by the 18.6-yr period oscillation of the lunar orbital inclination, and has therefore been hypothesized to influence bidecadal climate variability. In this study, the spatial distribution of diapycnal diffusivity together with its 18.6-yr oscillation estimated from a global tide model is incorporated into a state-of-the-art numerical coupled climate model to investigate its effects on climate variability over the North Pacific and to understand the underlying physical mechanism. It is shown that a significant sea surface temperature (SST) anomaly with a period of 18.6 years appears in the Kuroshio–Oyashio Extension region; a positive (negative) SST anomaly tends to occur during strong (weak) tidal mixing. This is first induced by anomalous horizontal circulation localized around the Kuril Straits, where enhanced modulation of tidal mixing exists, and then amplified through a positive feedback due to midlatitude air–sea interactions. The resulting SST and sea level pressure variability patterns are reminiscent of those associated with one of the most prominent modes of climate variability in the North Pacific known as the Pacific decadal oscillation, suggesting the potential for improving climate predictability by taking into account the 18.6-yr modulation of tidal mixing.