Analysis of venous flow transients for estimation of vascular resistance, compliance, and blood flow distribution

1987 ◽  
Vol 65 (9) ◽  
pp. 1884-1890 ◽  
Author(s):  
Richard I. Ogilvie ◽  
Danuta Zborowska-Sluis
Keyword(s):  
Time Constant ◽  
Venous Return ◽  
Fast Time ◽  
Slow Time ◽  
Venous Outflow ◽  
Venous Flow ◽  
Time Constants ◽  
Slow Time Constant ◽  
Over Time ◽  
Flow Transients

We analysed venous flow transients using a long venous circuit and right heart bypass in 17 dogs after a rapid decrease in atrial pressure. A biphase curve was obtained which we decomposed into a two-compartmental model, one with a fast time constant for venous return (0.069 min) and 52% of total circulating flow [Formula: see text], and one with a slower time constant (0.456 min) and 48% of [Formula: see text]. Subsequently, separate drainage from splanchnic and peripheral beds (with the renal venous return in the peripheral bed drainage) allowed comparison of time constants and venous outflow in these beds. The sum of the venous outflow volumes over time during separate drainage was indistinguishable from the single biphasic venous outflow volume curve over time observed with a long circuit and single reservoir. The fast time constant of the biphasic curve was not different from that determined by separate drainage from the peripheral circulation. The slow time constant of the single biphasic curve of 0.456 min was hybrid of two time constants, 0.216 min in the splanchnic bed and 0.862 min in the peripheral bed. Separate drainage from peripheral and splanchnic vascular beds demonstrated that the peripheral bed constituted 70% of venous outflow in the fast time constant compartment using Caldini's technique, whereas the splanchnic bed constituted 63% of venous outflow in the slow time constant compartment. It is concluded that, although Caldini's technique demonstrates biphasic venous flow transients, neither the fast nor the slow time constant compartments resolved from this analysis represent a particular anatomical region or vascular bed.

Comparative effects of vasodilator drugs on flow distribution and venous return

1985 ◽  
Vol 63 (11) ◽  
pp. 1345-1355 ◽  
Author(s):  
R. I. Ogilvie
Keyword(s):  
Blood Flow ◽  
Blood Volume ◽  
Time Constant ◽  
Venous Return ◽  
Flow Distribution ◽  
Fast Time ◽  
Central Blood Volume ◽  
Slow Time ◽  
Arterial Resistance ◽  
Slow Time Constant

Systemic vascular effects of hydralazine, prazosin, captopril, and nifedipine were studied in 115 anesthetized dogs. Blood flow [Formula: see text] and right atrial pressure (Pra) were independently controlled by a right heart bypass. Transient changes in central blood volume after an acute reduction in Pra at a constant [Formula: see text] showed that blood was draining from two vascular compartments with different time constants, one fast and the other slow. At three dose levels producing comparable reductions in systemic arterial pressure (30–40% at the highest dose), these drugs had different effects on flow distribution and venous return. Hydralazine and prazosin had parallel and balanced effects on arterial resistance of the two vascular compartments, and flow distribution was unaltered. Captopril preferentially reduced arterial resistance of the compartment with a slow time constant for venous return (−26 ± 6%, −30 ± 6%, −50 ± 5% at 0.02, 0.10, and 0.50 mg∙kg−1∙h−1, respectively; [Formula: see text]) without altering arterial resistance of the fast time-constant compartment. Blood flow to the slow time-constant compartment was increased 43 ± 14% at the highest dose, and central blood volume was reduced 108 ± 15 mL. In contrast, nifedipine had a balanced effect on arterial resistance with the lowest dose (0.025 mg/kg) but caused a preferential reduction in arterial resistance of the fast time-constant compartment at higher doses (−38 ± 4% and −55 ± 2% at 0.05 and 0.10 mg/kg, respectively). Blood flow to the slow time-constant compartment was reduced 36 ± 5% at the highest dose of nifedipine, and central blood volume was increased 66 ± 12 mL. Total systemic venous compliance was unaltered or slightly reduced by each of the four drugs. These results add further evidence to the hypothesis that peripheral blood flow distribution is a major determinant of venous return to the heart.

Time-constant histograms from the forced expired volume signal

1981 ◽  
Vol 51 (6) ◽  
pp. 1581-1593 ◽  
Author(s):  
R. L. Pimmel ◽  
T. K. Miller ◽  
J. M. Fouke ◽  
J. G. Eyles
Keyword(s):  
Time Constant ◽  
Vital Capacity ◽  
Compartment Model ◽  
Normal Subjects ◽  
Fast Time ◽  
Slow Time ◽  
Criterion Function ◽  
Time Constants ◽  
Nonnegativity Constraints ◽  
Slow Time Constant

The forced expired volume signal was analyzed using a parallel compartment model in which each compartment emptied exponentially. With this model the forced expired volume signal was represented by a histogram showing the fraction of the vital capacity as a functional of compartmental time constants. We developed an algorithm to compute this histogram from the volume signal. The algorithm used the least-squares criterion function with both smoothness and nonnegativity constraints. In a stimulation study reasonable histograms were obtained even in the presence of realistic random error. Three dependent forced expired volume signals from 16 subjects were analyzed, and the histograms were reproducible. Most histograms were bimodal with fast time constants of 0.12–0.55 s and slow time constants of 1.3–2.7 s. In all normal subjects and patients with restrictive disease more than 75% of the vital capacity was in the fast time-constant mode. Subjects with obstructive disease had more than 40% of the vital capacity in the slow time-constant mode.

scholarly journals Periodicity, time constants of drainage, and the mechanical determinants of peak cardiac output during exercise

2019 ◽  
Vol 127 (6) ◽  
pp. 1611-1619
Author(s):  
Sheldon Magder ◽  
Gabriel Famulari ◽  
Brian Gariepy
Keyword(s):  
Cardiac Output ◽  
Computational Model ◽  
Time Constant ◽  
Muscle Contractions ◽  
Fast Time ◽  
Fractional Flow ◽  
Time Constants ◽  
Peripheral Muscle ◽  
Muscle Region ◽  
Muscle Compartment

To analyze mechanical adaptations that must occur in the cardiovascular system to reach the high cardiac outputs known to occur at peak aerobic performance, we adapted a computational model of the circulation by adding a second parallel venous compartment as proposed by August Krogh in 1912. One venous compartment has a large compliance and slow time constant of emptying; it is representative of the splanchnic circulation. The other has a low compliance and fast time constant of emptying and is representative of muscle beds. Fractional distribution between the two compartments is an important determinant of cardiac output. Parameters in the model were based on values from animal and human studies normalized to a 70 kg male. The baseline cardiac output was set at 5 L/min, and we aimed for 25 L/min at peak exercise with a fractional flow to the peripheral-muscle region of 90%. Finally, we added the equivalent of a muscle pump. Adjustments in circuit and cardiac parameters alone increased cardiac output to only 15.6 L/min because volume accumulated in the muscle compartment and limited a higher cardiac output. Addition of muscle contractions decompressed the muscle region and allowed cardiac output to increase to 23.4 L/min. The pulsatility of blood flow imposes important constraints on the adaptations of cardiac and circulatory functions because it fixes the times for filling and emptying. Flow is further limited by the limits of cardiac filling on each beat. Muscle contractions play a key role by decompressing volume that would otherwise accumulate in the muscle vasculature and by decreasing the time for stroke return to the right ventricle. NEW & NOTEWORTHY We used a computational model of the circulation and previous human and animal data to model mechanical changes in the heart and circulation that are needed to reach the known high cardiac output at peak aerobic exercise. Key points are that time constants of drainage of circulatory compartments put limits on peak flow in a pulsatile system. Muscle contractions increase the rate of return to the heart and by doing so prevent accumulation of volume in the muscle compartment and greatly increase circulatory capacity.

scholarly journals Modulation of Voltage-dependent Properties of a Swelling-activated Cl− Current

1997 ◽  
Vol 110 (3) ◽  
pp. 313-325 ◽  
Author(s):  
Thomas Voets ◽  
Guy Droogmans ◽  
Bernd Nilius
Keyword(s):  
Time Constant ◽  
Single Channel ◽  
Fast Time ◽  
Channel Blockers ◽  
Inactivation Curve ◽  
Recovery From Inactivation ◽  
Double Exponential ◽  
Voltage Dependent ◽  
Slow Time Constant ◽  
External Ph

We used the patch-clamp technique to study the voltage-dependent properties of the swelling-activated Cl− current (ICl,swell) in BC3H1 myoblasts. This Cl− current is outwardly rectifying and exhibits time-dependent inactivation at positive potentials (potential for half-maximal inactivation of +75 mV). Single-channel Cl− currents with similar voltage-dependent characteristics could be measured in outside-out patches pulled from swollen cells. The estimated single-channel slope conductance in the region between +60 and +140 mV was 47 pS. The time course of inactivation was well described by a double exponential function, with a voltage-independent fast time constant (∼60 ms) and a voltage-dependent slow time constant (>200 ms). Recovery from inactivation, which occurred over the physiological voltage range, was also well described by a double exponential function, with a voltage-dependent fast time constant (10–80 ms) and a voltage-dependent slow time constant (>100 ms). The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl− concentration of the extracellular solution. Replacing extracellular Cl− by other permeant anions shifted the inactivation curve in parallel with their relative permeabilities (SCN− > I− > NO3− > Cl− >> gluconate). A leftward shift of the inactivation curve could also be induced by channel blockers. Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation. In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH , external divalent cations, and by the nature of the permeant anion.

Short-term potentiation of ventilation after different levels of hypoxia

1999 ◽  
Vol 86 (5) ◽  
pp. 1478-1482 ◽  
Author(s):  
Astryd A. Menendez ◽  
Thomas J. Nuckton ◽  
José E. Torres ◽  
David Gozal
Keyword(s):  
Time Constant ◽  
Minute Ventilation ◽  
System Stability ◽  
Fast Time ◽  
Short Term ◽  
Ventilatory Responses ◽  
Term Potentiation ◽  
Best Fit ◽  
Slow Time Constant ◽  
Different Levels

Short-term potentiation of ventilation (VSTP) may be observed in healthy subjects on sudden termination of an hypoxic stimulus. We hypothesized that the level of hypoxia preceding normoxia would modify the duration and magnitude of the ensuing ventilatory decay. Ten healthy adults were studied on two different occasions, during which they were randomly exposed to isocapnic 6 or 10% O2for 60 s and then switched to an isocapnic normoxic gas mixture. Both hypoxic gases induced significant ventilatory responses, and mean peak minute ventilation before the isocapnic normoxic switch was higher in 6% O2( P < 0.001). The fast time constant of the two-exponential equation representing the best fit for ventilatory decay was unaffected by the magnitude of the hypoxic stimulus. However, the slow time constant, which is considered to represent VSTP, was markedly prolonged in 6% compared with 10% O2 [106.7 ± 11.3 vs. 38.2 ± 6.1 (SD) s, respectively; P< 0.0001]. This result indicates that VSTP is stimulus dependent. We conclude that the magnitude of hypoxia preceding a normoxic transient modifies VSTP characteristics. We speculate that the interdependence function of ventilatory stimulus and short-term potentiation is crucial for preservation of system stability during transitions from high to low ventilatory drives.

Compartmental vascular changes in dogs after nephrectomy, DOCA, and saline: effect of nifedipine

1987 ◽  
Vol 65 (9) ◽  
pp. 1891-1897 ◽  
Author(s):  
Richard I. Ogilvie ◽  
Danuta Zborowska-Sluis
Keyword(s):  
Time Constant ◽  
Venous Return ◽  
Flow Distribution ◽  
Filling Pressure ◽  
Fast Time ◽  
Mean Circulatory Filling Pressure ◽  
Hypertensive Group ◽  
Arteriolar Resistance ◽  
The Mean ◽  
Overall Resistance

Hypertension (mean arterial pressure, (MAP) 131 ± 3 mmHg) developed in 18 dogs 4 weeks after left nephrectomy, deoxycorticosterone acetate (DOCA), 5 mg/kg sc twice weekly), and 0.5% NaCl drinking solution. This can be compared with MAP (95 ± 7 mmHg) of 13 dogs with nephrectomy alone and MAP (86 ± 4 mmHg) of 25 dogs without nephrectomy. The two-compartment model of the circulation revealed no differences in systemic vascular compliance, compartmental compliance, or flow distribution to the compartments. However, the time constant for venous return for the compartment with the rapid time constant was increased from 0.05 ± 0.004 min in control animals to 0.07 ± 0.006 min in the nephrectomy alone group and 0.09 ± 0.008 min in the hypertensive group (p < 0.001), as a result of an increase in venous resistance. Arteriolar resistance in this compartment was also increased in the hypertensive animals, as was the mean circulatory filling pressure and overall resistance to venous return. Nifedipine (0.025–0.05 mg/kg) reduced MAP by 15% in the nephrectomy alone group and by 22% in the hypertensive group, with reduction in arteriolar resistance only in the fast time constant compartment. In the slow time constant compartment, arteriolar resistance was increased by more than 100% and flow decreased by more than 50% after nifedipine. Unilateral nephrectomy, DOCA, plus NaCl resulted in hypertension by increasing arteriolar resistance in a vascular compartment with a fast time constant for venous return. Nifedipine countered this effect by inducing arteriolar vasodilation in this compartment. In addition, nifedipine reduced the mean circulatory filling pressure and overall resistance to venous return.

scholarly journals Individual motion perception parameters and motion sickness frequency sensitivity in fore-aft motion

2021 ◽  
Author(s):  
Tugrul Irmak ◽  
Ksander N. de Winkel ◽  
Daan M. Pool ◽  
Heinrich H. Bülthoff ◽  
Riender Happee
Keyword(s):  
Motion Sickness ◽  
Motion Perception ◽  
Time Constant ◽  
Storage Time ◽  
Velocity Storage ◽  
Strong Positive Correlation ◽  
Subjective Vertical ◽  
Time Constants ◽  
Frequency Sensitivity ◽  
Observer Model

AbstractPrevious literature suggests a relationship between individual characteristics of motion perception and the peak frequency of motion sickness sensitivity. Here, we used well-established paradigms to relate motion perception and motion sickness on an individual level. We recruited 23 participants to complete a two-part experiment. In the first part, we determined individual velocity storage time constants from perceived rotation in response to Earth Vertical Axis Rotation (EVAR) and subjective vertical time constants from perceived tilt in response to centrifugation. The cross-over frequency for resolution of the gravito-inertial ambiguity was derived from our data using the Multi Sensory Observer Model (MSOM). In the second part of the experiment, we determined individual motion sickness frequency responses. Participants were exposed to 30-minute sinusoidal fore-aft motions at frequencies of 0.15, 0.2, 0.3, 0.4 and 0.5 Hz, with a peak amplitude of 2 m/s2 in five separate sessions, approximately 1 week apart. Sickness responses were recorded using both the MIsery SCale (MISC) with 30 s intervals, and the Motion Sickness Assessment Questionnaire (MSAQ) at the end of the motion exposure. The average velocity storage and subjective vertical time constants were 17.2 s (STD = 6.8 s) and 9.2 s (STD = 7.17 s). The average cross-over frequency was 0.21 Hz (STD = 0.10 Hz). At the group level, there was no significant effect of frequency on motion sickness. However, considerable individual variability was observed in frequency sensitivities, with some participants being particularly sensitive to the lowest frequencies, whereas others were most sensitive to intermediate or higher frequencies. The frequency of peak sensitivity did not correlate with the velocity storage time constant (r = 0.32, p = 0.26) or the subjective vertical time constant (r = − 0.37, p = 0.29). Our prediction of a significant correlation between cross-over frequency and frequency sensitivity was not confirmed (r = 0.26, p = 0.44). However, we did observe a strong positive correlation between the subjective vertical time constant and general motion sickness sensitivity (r = 0.74, p = 0.0006). We conclude that frequency sensitivity is best considered a property unique to the individual. This has important consequences for existing models of motion sickness, which were fitted to group averaged sensitivities. The correlation between the subjective vertical time constant and motion sickness sensitivity supports the importance of verticality perception during exposure to translational sickness stimuli.

Interactions between Cognition, Compression, and Listening Conditions: Effects on Speech-in-Noise Performance in a Two-Channel Hearing Aid

2007 ◽  
Vol 18 (07) ◽  
pp. 604-617 ◽  
Author(s):  
Thomas Lunner ◽  
Elisabet Sundewall-Thorén
Keyword(s):  
Speech Recognition ◽  
Test Scores ◽  
Pure Tone ◽  
Hearing Aid ◽  
Test Procedure ◽  
Performance Measure ◽  
Cognitive Test ◽  
Fast Time ◽  
Time Constants ◽  
Pure Tone Average

This study which included 23 experienced hearing aid users replicated several of the experiments reported in Gatehouse et al (2003, 2006) with new speech test material, language, and test procedure. The performance measure used was SNR required for 80% correct words in a sentence test. Consistent with Gatehouse et al, this study indicated that subjects showing a low score in a cognitive test (visual letter monitoring) performed better in the speech recognition test with slow time constants than with fast time constants, and performed better in unmodulated noise than in modulated noise, while subjects with high scores on the cognitive test showed the opposite pattern. Furthermore, cognitive test scores were significantly correlated with the differential advantage of fast-acting versus slow-acting compression in conditions of modulated noise.The pure tone average threshold explained 30% of the variance in aided speech recognition in noise under relatively simple listening conditions, while cognitive test scores explained about 40% of the variance under more complex, fluctuating listening conditions, where the pure tone average explained less than 5% of the variance. This suggests that speech recognition under steady-state noise conditions may underestimate the role of cognition in real-life listening.

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