Short time constant for rate-dependent changes of atrioventricular conduction in dogs

1981 ◽  
Vol 241 (1) ◽  
pp. H26-H33 ◽  
Author(s):  
J. Billette
Keyword(s):  
Time Constant ◽  
Refractory Period ◽  
Atrioventricular Conduction ◽  
Conduction Time ◽  
Short Cycle ◽  
Recovery Curve ◽  
Rate Dependent ◽  
Induction Study ◽  
Anesthetized Dogs ◽  
Short Time

The number of short cardiac cycles necessary to induce, and normal cycles to dissipate, a rate-dependent shortening in atrioventricular (AV) nodal functional refractory period (FRP) and conduction time (CT) was determined in six anesthetized dogs. For the induction study, the periodic premature stimulation procedure was performed at control and repeated six times while 1, ..., 6 conditioning short prepremature cycles (PPC) were introduced between the last basic cycle and the premature cycle. In all dogs, FRP was maximally shortened and the recovery curve was maximally shifted to the left when the premature cycle was preceded by 1 PPC. Adding 2, ..., 6 PPC resulted in slightly fewer but persistent shortenings of both FRP and CT. The dissipation of the FRP and CT shortenings produced by 2 and 6 PPC was studied subsequently in the same dogs by introducing 1, ..., 6 normal basic cycles between the last PPC and the test premature cycle. The FRP and CT shortenings induced by 2 or 6 PPC were almost completely dissipated after one normal basic cycle. Thus, one short cycle produces a maximum shortening in AV nodal FRP and CT, and one normal basic cycle is sufficient to dissipate these effects.

Rate-dependent functional properties of retrograde atrioventricular nodal conduction in experimental animals

1993 ◽  
Vol 265 (4) ◽  
pp. H1257-H1264 ◽  
Author(s):  
G. O'Hara ◽  
R. Gendreau ◽  
J. Billette ◽  
F. Amellal ◽  
M. Nayebpour ◽  
...  
Keyword(s):  
Functional Properties ◽  
Time Constant ◽  
Refractory Period ◽  
Conduction Time ◽  
Experimental Animals ◽  
Rate Dependent ◽  
Activation Rate ◽  
Anesthetized Dogs ◽  
Atrioventricular Nodal Conduction ◽  
Conduction Properties

While rate-dependent atrioventricular (AV) nodal functional properties play a major role in determining antegrade AV nodal conduction, their existence and characteristics have not been assessed during retrograde AV nodal impulse propagation. Pacing protocols were used to study selectively AV nodal recovery, facilitation, and fatigue in 6 isolated, superfused rabbit AV nodal preparations and in 11 morphine-chloralose anesthetized dogs. All three properties were identifiable during retrograde AV nodal activation in rabbits. Retrograde recovery and fatigue were clearly demonstrated in dogs, but facilitation could not be evaluated because of echo beats during retrograde premature stimulation. Functional properties were qualitatively similar during retrograde and antegrade propagation; however, important quantitative differences were noted. The time constant for recovery from activation was significantly greater in the retrograde [rabbits, 69 +/- 8 (SE) ms; dogs, 93 +/- 11 ms] compared with the antegrade direction (rabbits, 50 +/- 5 ms; dogs, 58 +/- 4 ms; P < 0.05 vs. retrograde for each species). The magnitude of fatigue resulting from sustained increases in rate was also substantially greater in the retrograde direction in both rabbits (17 +/- 2 vs. 10 +/- 1 ms antegrade, P = 0.01) and dogs (20 +/- 4 vs. 6 +/- 1 ms antegrade, P < 0.01). Conduction time and refractory period were both greater in the retrograde compared with antegrade direction, and directional differences in conduction properties were magnified as activation rate increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of diltiazem on atrioventricular conduction and arterial blood pressure: correlation with plasma drug concentrations

1984 ◽  
Vol 62 (12) ◽  
pp. 1479-1486 ◽  
Author(s):  
Jean-Paul Clozel ◽  
Jacques Billette ◽  
Gilles Caillé ◽  
Pierre Théroux ◽  
Richard Cartier
Keyword(s):  
Blood Pressure ◽  
Plasma Concentration ◽  
Refractory Period ◽  
Plasma Concentrations ◽  
Atrioventricular Conduction ◽  
Gas Liquid Chromatography ◽  
Conduction Time ◽  
Arterial Blood ◽  
Drug Concentrations ◽  
Atrial Conduction Time

Atrial and atrioventricular conduction variables were studied at control and at the end of each of six consecutive 45-min diltiazem administration periods in eight closed chest-anesthetized dogs. Diltiazem was given as a bolus (50 μg/kg, i.v.) followed by an infusion (0.5 μg∙kg−1∙min−1); doses were doubled in subsequent periods. The plasma concentrations, measured by gas–liquid chromatography, ranged from 8 to 1400 ng/mL and correlated strongly with the doses (r = 0.92; p < 0.01). The Wenckebach cycle length, basic conduction time, and functional refractory period of the atrioventricular (AV) node increased proportionally with plasma concentration (respective r = 0.90, 0.89, 0.80; p < 0.01). The minimum mean plasma concentrations affecting these variables significantly were 37, 83, and 175 ng/mL, respectively. Second or third degree AV blocks developed in all dogs for plasma concentrations between 379 and 1400 ng/mL. In four dogs which were given isoproterenol (0.2 μg∙kg−1∙min−1), these blocks disappeared within 1 min. Atrial conduction time and functional refractory period were slightly but significantly shortened by diltiazem with mean plasma concentrations of 175 ng/mL and over. His–Purkinje intervals were not significantly changed by diltiazem. Systolic and diastolic arterial pressures were decreased by diltiazem (r = −0.64, r = −0.79; p < 0.01) starting with a mean plasma concentration of 83 ng/mL. We conclude that AV nodal conduction variables are progressively prolonged with increasing plasma concentrations of diltiazem; plasma concentrations affecting blood pressure and AV nodal variables overlap; and the AV blocks produced by toxic concentrations of diltiazem can be corrected by isoproterenol.

Separate parasympathetic control of heart rate and atrioventricular conduction of dogs

1990 ◽  
Vol 259 (2) ◽  
pp. H536-H542 ◽  
Author(s):  
D. W. Wallick ◽  
P. J. Martin
Keyword(s):  
Vena Cava ◽  
Atrioventricular Conduction ◽  
Conduction Time ◽  
Fat Pad ◽  
Av Node ◽  
Parasympathetic Ganglia ◽  
Anesthetized Dogs ◽  
Parasympathetic Control ◽  
The Right ◽  
Electrical Stimuli

In open-chest, autonomically decentralized, anesthetized dogs, a brief burst of electrical stimuli was delivered at various time delays to the right pulmonary vein (RPV) fat pad. This fat pad contains parasympathetic ganglia that innervate the sinoatrial (SA) node. Each burst elicited a bimodal increase in the cardiac cycle length (CCL) without eliciting a significant change in atrioventricular conduction time (AVCT). A similar burst was applied to the inferior vena cava-inferior left atrial fat pad. This fat pad contains nerves that innervate the AV node. This latter stimulation elicited a bimodal increase in AVCT without eliciting any change in the CCL. When the cervical vagi were stimulated in a similar manner, a bimodal increase in the CCL was elicited that was similar to the response we observed when the RPV fat pad was stimulated. In contrast, the dromotropic response was quite variable. In conclusion, we could, for the most part, elicit selective parasympathetic control of either the SA or the AV node, respectively.

Quantitation of dynamic AV nodal properties and application to predict rate-dependent AV conduction

1991 ◽  
Vol 261 (2) ◽  
pp. H292-H300 ◽  
Author(s):  
M. Nayebpour ◽  
M. Talajic ◽  
S. Nattel
Keyword(s):  
Time Constant ◽  
Exponential Function ◽  
Conduction Time ◽  
Quantitative Characterization ◽  
First Order ◽  
Rate Dependent ◽  
Av Conduction ◽  
Coupling Interval ◽  
Premature Beats ◽  
Nodal Properties

A number of functional properties of the atrioventricular (AV) node have been described in response to changes in the atrial input rate. The purpose of this study was 1) to develop quantitative descriptors of these properties, and 2) to determine whether they can account for rate-dependent changes in AV nodal conduction. The delay in AV nodal conduction of single premature beats (recovery) was found to be an exponential function of coupling interval with a time constant of 66 +/- 2 (+/- SE) ms. A single abbreviated (facilitation) cycle did not alter the time constant of recovery or basal conduction for a subsequent beat but shifted its recovery curve to the left to an extent exponentially related to the facilitation cycle length. The induction of a tachycardia with HA interval fixed so as to control the recovery and facilitation variables resulted in a first-order onset of AV conduction slowing (fatigue). The fatigue process had a time constant in the range of 70 beats and a magnitude that was a decaying exponential function of HA interval. An equation incorporating quantitative descriptors of recovery, facilitation, and fatigue accurately predicted rate-dependent changes in AH interval. We conclude that 1) the AV nodal properties of recovery, facilitation, and fatigue are amenable to quantitative characterization, and 2) rate-dependent changes in AV nodal conduction time can be well described in terms of these underlying properties.

Facilitated ventriculoatrial conduction: effects of sequential pacing interval and basic cycle length

1995 ◽  
Vol 268 (1) ◽  
pp. H384-H390
Author(s):  
A. F. Kuguoglu ◽  
D. W. Wallick ◽  
P. J. Martin
Keyword(s):  
Refractory Period ◽  
Cycle Length ◽  
Effective Refractory Period ◽  
Conduction Time ◽  
Time Intervals ◽  
Av Node ◽  
Anesthetized Dogs ◽  
Alpha Chloralose ◽  
Retrograde Conduction ◽  
Basic Cycle Length

We studied 1) the effects of pacing interval, 2) the timing of atrioventricular sequential pacing, and 3) the effects of successive premature intervals on retrograde conduction of the atrioventricular (AV) node in open-chest alpha-chloralose-anesthetized dogs. The ventricles and atria were sequentially paced at one of three levels of basic cycle length and one of six sequential time intervals (V1-A1) for three basic cycles (V1-V1). Then a premature ventricular impulse was introduced at various V1-V2 intervals, and the resultant retrograde conduction time (V2-A2 interval) was measured. Successive V1-V2 intervals were applied in an incremental or a decremental fashion. The V1-V2 intervals ranged from V1-V1 to V1-V2, at which the retrograde conduction was blocked. For each level of the above three factors, we plotted retrograde conduction time (V2-A2) as a function of the various premature intervals (V1-V2). We found that the time between atrial and ventricular activations was the most important factor in determining V1-V2 and in decreasing the effective refractory period of the AV node during retrograde conduction.

scholarly journals A sensory integration account for time perception

2020 ◽  
Author(s):  
Alessandro Toso ◽  
Arash Fassihi ◽  
Luciano Paz ◽  
Francesca Pulecchi ◽  
Mathew E. Diamond
Keyword(s):  
Time Perception ◽  
Time Constant ◽  
Sensory Integration ◽  
Neuronal Firing ◽  
Elapsed Time ◽  
Leaky Integrator ◽  
Long Time ◽  
Integrator Model ◽  
Short Time ◽  
Sense Of Touch

ABSTRACTThe connection between stimulus perception and time perception remains unknown. The present study combines human and rat psychophysics with sensory cortical neuronal firing to construct a computational model for the percept of elapsed time embedded within sense of touch. When subjects judged the duration of a vibration applied to the fingertip (human) or whiskers (rat), increasing stimulus mean speed led to increasing perceived duration. Symmetrically, increasing vibration duration led to increasing perceived intensity. We modeled spike trains from vibrissal somatosensory cortex as input to dual leaky integrators – an intensity integrator with short time constant and a duration integrator with long time constant – generating neurometric functions that replicated the actual psychophysical functions of rats. Returning to human psychophysics, we then confirmed specific predictions of the dual leaky integrator model. This study offers a framework, based on sensory coding and subsequent accumulation of sensory drive, to account for how a feeling of the passage of time accompanies the tactile sensory experience.

scholarly journals Atrioventricular Conduction Time in Fetuses Assessed by Doppler Echocardiography

2011 ◽  
pp. 611-616 ◽  
Author(s):  
V. TOMEK ◽  
J. JANOUŠEK ◽  
O. REICH ◽  
J. GILÍK ◽  
R. A. GEBAUER ◽  
...  
Keyword(s):  
Heart Rate ◽  
Reference Values ◽  
Gestational Age ◽  
Doppler Echocardiography ◽  
Fetal Heart ◽  
Atrioventricular Conduction ◽  
Time Interval ◽  
Conduction Time ◽  
Time Intervals ◽  
Normal Limits

We performed measurement of mechanical atrioventricular conduction time intervals in human fetuses assessed by Doppler echocardiography and provided reference values. We found that atrioventricular conduction time interval was prolonged with gestational age and decreased with increasing fetal heart rate. No correlation between gestational age and heart rate was found. Using normal limits established by this study, mechanical atrioventricular interval >135 ms in the 20th week and/or >145 ms in the 26th week of gestation could be suspected of having the first-degree AV block. We compared reference values with fetuses of mothers with anti-SSA Ro/SSB La autoantibodies, being in risk of isolated congenital heart block development. One of 21 fetuses of mothers with positive autoantibodies was affected by prolonged atrioventricular interval according to the established limits, with sinus rhythm after the birth.

346. Measurements of the rate of change of temperature in high temperature-short time pasteurization plant

1947 ◽  
Vol 15 (1-2) ◽  
pp. 18-23
Author(s):  
F. Steghart
Keyword(s):  
High Temperature ◽  
Time Constant ◽  
Rate Of Change ◽  
Hot Water ◽  
Water Pipe ◽  
Temperature Changes ◽  
Rates Of Change ◽  
High Temperature Short Time ◽  
Short Time

It has recently been claimed that in modern high temperature-short time pasteurization plant fluctuations in temperature of the order of 1° F./sec. are unusual and probably artefacts, and that an instantaneous drop is certainly fictitious.It has, nevertheless, been shown that such rapid drops in temperature do in fact occur frequently in high temperature-short time plants of the type investigated. The plant investigated was not of the latest design incorporating devices for speeding up the control by injecting steam directly into the hot-water pipe.Temperature changes of the order of those in question were first observed by Mattick & Hiscox(1) of the National Institute for Research in Dairying, who carried out tests on pasteurization plant using a small mirror galvanometer with a very short time constant. The maximum rates of change were, however, not observed.

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