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Biomedical subjects

M Kollai

Publications and source records attributed to M Kollai.

43 records · Page 3Linked to original sources
PubMed1975

Specific baroreceptor control of vertebral and cardiac sympathetic activity.

The effect of bilateral carotid occlusion (BCO) on the activity of the vertebral and cardiac sympathetic efferent nerves was studied in gallamine-immobilized and artificially ventilated cats under chloralose-urethane anaesthesia. Electrical activity of the vertebral and cardiac nerves (VNA and CNA), their integram, arterial blood pressure and respiration were recorded. BCO led to an increase in VNA persisting throughout the occlusion period, while merely a transient increase took place in CNA. When blood pressure was kept at a constant level or the depressor nerves was transected, CNA responded to BCO with a lasting increase. Electrical stimulation of the central stump of the left depressor nerve inhibited CNA much more than VNA. It is assumed that the selective inhibition of CNA, after a transient increase, arises as a consequence of a rise in blood pressure, i.e. of consecutive aortic baroreceptor excitation.

Action Potentials↗
PubMedDate not supplied

Neural control of the heart: significance of double innervation re-examined.

Our recent studies on the activity of cardiac sympathetic and vagal nerves in anesthetized dogs have revealed that control of these two autonomic nerves having 'antagonistic' action on the heart is not always reciprocal; both reciprocal and non-reciprocal controls exist in reflex as well as in adaptive responses. We have evidence which also suggests the functional significance of non-reciprocal control. The co-activation of both autonomic efferents to the heart is particularly useful in increasing cardiac output as, for example, in the chemoreceptor reflex. On the other hand, under 'normal' conditions the respiration related rhythmic activity of both sympathetic and vagal nerves is almost completely reciprocal. The loss of the reciprocity occurs under subnormal conditions in which sympathetic discharges shift so that both nerves fire simultaneously. This tends to reduce respiration-induced fluctuations in heart rate. During cardiac rhythms seen in the efferent nerve activity, the peak of vagal firing does not strictly coincide with the inhibitory period of the sympathetic activity; vagal impulses reach the heart slightly earlier. However, when the heart rate is irregular and slow, the vagal activity shifts in time so that it coincides more definitely with the period of sympathetic nerve inhibition. This tends to further augment rhythmic fluctuations in heart rate. These studies show that the centers involved employ both reciprocal and non-reciprocal control of cardial nerve activity in reactions regulating heart function. The relationship between discharge patterns of both autonomic nerves is involved in production of fluctuation of heart rate in normal as well as in subnormal conditions.

Animals↗
PubMedDate not supplied

Effect of cardiac vagal and sympathetic nerve activity on heart rate in rhythmic fluctuations.

Beat-to-beat changes observed in cardiac vagal and sympathetic nerve activity and their effects on cardiac cycle length were studied during slow wave blood pressure and heart rate fluctuations (third order rhythm) and during respiratory sinus arrhythmia. Recordings were made from both nerves simultaneously in chloralose anesthetized and artificially ventilated dogs. During slow wave fluctuations in heart rate, a linear relationship was found to exist between the number of spikes per pulse interval recorded from vagal and sympathetic nerves and the length of pulse intervals. During respiratory sinus arrhythmia the time course of rhythmic changes in nerve activity and in cardiac cycle length was analyzed. Comparison of time courses indicated that vagal discharges affected the timing of not the following beat, but the one after; while the sympathetic effect was further delayed, affecting the third beat after the discharge. Baroreceptor stimulation, which resulted in lengthening the cardiac cycle, shifted this relationship by one cycle, i.e. vagal discharges affecting the occurrence of the following beat, while sympathetic discharges affecting the beat after. These results provide evidence for the conclusion that in dogs both vagal and sympathetic nerve activity contribute to the control of cardiac cycle length, however, with different time relations and effectiveness.

Animals↗
PubMedDate not supplied

Static versus dynamic distensibility of the carotid artery in humans.

In clinical studies, the elastic behavior of central arteries is usually assessed by measuring dynamic distensibility. In this study, we aimed to investigate how dynamic and static distensibility of the common carotid artery (D(dyn) and D(stat), respectively) are related in 28 healthy volunteers of 20-71 years. The carotid diameter and its change with the pressure pulse were measured using an ultrasound echo-tracking device. Arterial blood pressure was measured by Finapres and carotid pressure was determined by applanation tonometry. D(dyn) was determined at rest using the pressure pulse, while D(stat) was determined during pressor responses induced by handgrip or cold pressor test. Data are given as mean +/- 1 SD. In younger subjects (<35 years), D(stat) did not differ from D(dyn) (7.0 +/- 3.4 vs. 6.5 +/- 2.1 x 10(-3) x mm Hg(-1), respectively), whereas in older subjects (>35 years), D(stat) was significantly higher than D(dyn) (3.8 +/- 1.4 vs. 2.1 +/- 0.9 x 10(-3) x mm Hg(-1), p < 0.001). For all subjects, D(stat) and D(dyn) decreased with increasing age and mean arterial pressure (MAP). Using stepwise multiple regression analysis, the strongest predictor of D(stat) proved to be MAP, while that of D(dyn) was age. D(stat) was found to be linearly related to the hysteresis loop area of the pressure-diameter relation (r = 0. 94), i.e. to vessel wall viscosity. It is concluded that, with increasing age, static distensibility overestimates the distension capacity of large arteries.

Adult↗