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H S Sarajas

Publications and source records attributed to H S Sarajas.

17 recordsLinked to original sources
PubMed1990

Regulation of heart rate variation by the autonomic nervous system in neonatal lambs.

We studied the role of the autonomic nervous system in the regulation of heart rate variation (HRV) in 12 chronically instrumented neonatal lambs. HRV was quantified from ECG tracings by computing periodic HRV distributions at frequencies of 0.02-1.00 Hz, using power spectral analysis of heart rate, and also by HRV indices. Heart rate declined more during the 1st than the 2nd mo after birth. Multiple regression analysis showed that the heart rate responses to vagal and to beta-adrenergic blockade had an independent negative association both with age and with the initial mean heart rate, whereas the overall HRV response had a positive association with age. Vagal blockade led to a 70-80% decrease in the beat-to-beat HRV in all lambs (p less than 0.001). The overall HRV indices decreased by 40-65% in lambs (less than 30 d old (p less than 0.001) and about 30% in those greater than 30 d old (p less than 0.05). In the power spectrum the greatest decrease was seen in the high-frequency components of HRV. beta-Blockade led to a decrease of about 50% in all HRV (p less than 0.001) in the younger lambs, without frequency selection. In the older lambs, it had no effect on the beat-to-beat HRV, but the overall HRV (coefficient of variance) decreased maximally by 40% (p less than 0.01), with a significant reduction in the low-frequency components of HRV. These results suggest that in the regulation of HRV after birth dual control via the autonomic nervous system is most important. In the older lambs, developmental changes result in precise regulation of the fast heart rate fluctuations mainly by the vagal division, whereas the slow fluctuations are partially regulated by the vagal and beta-adrenergic divisions.

Animals↗
PubMed1984

Heart rate variation in relation to age and sleep state in neonatal lambs.

The heart rate (HR), heart rate variation (HRV) and the power spectrum of the HR were studied in 1 to 10-week-old neonatal lambs. The average HR was highest and the indices of the HRV were lowest at the age of 1 to 3 weeks. However, there was a decreasing trend in the overall HRV with advancing age when it was normalized in relation to the average HR. The absolute beat-to-beat HRV increased after the age of 3 weeks; it remained the same when normalized in relation to the HR. The overall HRV was highest during waking and active sleep; it was lowest during quiet sleep. The beat-to-beat HRV was lower during quiet sleep than during active sleep. Three major peaks of HRV power were detected in the spectra of all lambs. During active sleep the HRV power increased at all frequencies ranging from 0 to 1.0 Hz. During waking the low-frequency HRV power was primarily increased. The high-frequency HRV was pronounced during quiet sleep and the state of sleepy waking, especially at the age of 4 to 6 weeks. Our study indicates that developmental factors and the sleep state have to be considered when HR patterns are experimentally investigated. Many similarities between the HR control of neonatal lambs and that of human neonates make it feasible to study the mechanisms of clinical HRV patterns by lamb experiments.

Age Factors↗
PubMed1980

Distension of pulmonary vein--left atrial junction: heart rate responses in conscious and anesthetized dogs.

The cardiac chronotropic effects of distension of pulmonary vein-left atrial junction were investigated in conscious dogs and in dogs anesthetized with intravenous alpha-chloralose (100 mg/kg) or pentobarbital (30 mg/kg). All the experiments were made on trained, chronically instrumented, closed chest animals held in horizontal position. Inflation of a single small balloon in the junction elicited a tachycardic response both in conscious and chloralose-anesthetized dogs, while in pentobarbital anesthesia no change in heart rate was found. Contrary to reports of other investigators, no transient bradycardia was found, nor any correlation between predistension heart rate and the increase in heart rate due to the distension. It is suggested that the choice of anesthetic can be done only after its modifying effect on the parameter studied is known. Only the use of trained, chronically instrumented and conscious dogs will reveal this effect.

Animals↗
PubMed1978

Suppresion of autonomic postganglionic discharges by pentobarbital in dogs, with or without endotoxemia.

Initial effects of pentobarbital (8 mg/kg) on autonomic efferent and afferent discharge rates were studied in 26 dogs under morphine-chloralose anesthesia. Half of the dogs were given endotoxin E. coli (1 mg/kg) before pentobarbital. The postganglionic cervical vagal efferentation of all the dogs decreased as did the postganglionic cardiac sympathetic efferentation. The heart rate of the dogs given endotoxin decreased, while an increase in heart rate with abolition of respiratory arrhythmia, was observed in dogs without endotoxin. The aortic pressure of the former dogs dropped while it fell only slightly in the latter ones. The aortic arch baroreceptor activity decreased while the changes of left atrial B-type receptor activity were not significant. The changes of the left atrial and central venous pressures were slight but those of the pulmonary arterial pressure generally paralleled the changes in the aortic pressure. Pentobarbital, accordingly, seems to exert both sympatholytic and vagolytic effects. These explain the heart rate changes, as well as the impaired cardiac contractility it evokes. The obvious impairment of cardiovascular control mechanisms by pentobarbital should be seriously considered in investigations into the cardiovascular control.

Action Potentials↗
PubMed1977

Circulatory reflex responses during the initial stage of feline endotoxin shock.

Cardiovascular and autonomic nervous responses to an injection of E. coli endotoxin were followed for up to 15 min. in cats anesthetized with chloralose and given artificial respiration. Within 60 seconds, endotoxin induced a drop of aortic pressure, with simultaneous cardiac acceleration and slight central venous hypertension. There was an associated, almost complete cessation of the aortic arch baroreceptor afferentation. The cardiac sympathetic efferentation increased up to 1.4 times the control level at its maximum. The splenic sympathetic efferentation increased up to 10.6 times the control level at the end of the 15 min period, when the other parameters studied showed a trend to control level. The sympathetic autonomic system seems to be activated through cardiovascular receptors sensing hemodynamic changes touched off by endotoxin-induced release of vasoactive substances.

Animals↗