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Biomedical subjects

M Kollai

Publications and source records attributed to M Kollai.

At least 37 records · Page 2Linked to original sources
PubMed1993

Respiratory sinus arrhythmia, cardiac vagal tone, and respiration: within- and between-individual relations.

Respiratory sinus arrhythmia (RSA) is frequently employed as an intra- and interindividual index of cardiac parasympathetic tone, although the relationship of RSA to interindividual differences in cardiac vagal tone remains questionable. Our study examined between- and within-subject relations among RSA, cardiac vagal tone, and respiratory parameters. Twenty-nine young adults performed two sessions of tasks under no medication and single and double autonomic blockade (intravenously administered propranolol and atropine). Parasympathetic tone was determined from heart period responses to complete vagal blockade. Results indicated the following. Resting RSA does not accurately predict individual differences in cardiac vagal tone. However, RSA and heart period together do predict such individual differences reasonably well. The relationship between individual variations in RSA and vagal tone is not improved by controlling respiratory parameters. Substantial cardiac vagal activity occurs during inspiration, and intraindividual variations in respiratory measures confound the association between RSA and cardiac vagal tone.

Adolescent↗
PubMed1992

Multiple modes of operation of cardiac autonomic control: development of the ideas from Cannon and Brooks to the present.

Since Cannon's time much emphasis has been placed on reciprocal control of the organ function by the autonomic nerves while other modes of control has been neglected. In our laboratory, prompted by Dr. Brooks, we initiated the study of the autonomic control of the heart by recording simultaneously the activity of cardiac sympathetic and parasympathetic nerves under a variety of conditions in chloralose anesthetized dogs. We have demonstrated that the central nervous system exercises reciprocal as well as non-reciprocal pattern of control over the two arms of the autonomic outflows under different physiological and behavioral conditions, and that each mode of control has an important functional significance.

Animals↗
PubMed1992

Cardiac vagal tone in generalised anxiety disorder.

The aim of the present study was twofold: firstly, to determine cardiac vagal tone in subjects with generalised anxiety disorder directly, using an invasive pharmacological method; and secondly, to test whether the non-invasive method of measuring the amplitude of respiratory sinus arrhythmia (RSA) gives a reliable estimate of cardiac vagal tone in this form of anxiety disorder. Comparison of baseline physiological measures of anxious and control subjects revealed that cardiac vagal tone and heart rate were not different in the two groups of subjects, whereas length of the respiratory cycle and amplitude of respiratory sinus arrhythmia were reduced in the former group. Because of the higher respiratory rates of anxious subjects, the RSA method was found to underestimate cardiac vagal tone in generalised anxiety disorder.

Adult↗
PubMed1990

Respiratory sinus arrhythmia is a limited measure of cardiac parasympathetic control in man.

1. Respiratory modulation of cardiac parasympathetic activity and the relationship between respiratory sinus arrhythmia and parasympathetic control has been studied in twenty-nine conscious, healthy young adult subjects. 2. Changes in heart period in propranolol-treated subjects were taken as the measure of changes in cardiac parasympathetic activity; respiratory sinus arrhythmia was quantified as the difference between maximum and minimum heart periods in a given respiratory cycle; cardiac parasympathetic control was defined as the change in heart period after administration of a full dose of atropine. 3. During normal quiet breathing the inspiratory level of cardiac parasympathetic activity was not reduced to zero. The expiratory level was influenced by excitatory inputs whose activation was related to respiratory cycle length. 4. Slow breathing was associated with augmented sinus arrhythmia, but in different individuals the influence on minimum and maximum heart periods varied so that mean heart period was increased in some subjects but decreased in others. This occurred both in control conditions and after administration of a full dose of propranolol. 5. During normal breathing the correlation across subjects between respiratory sinus arrhythmia and parasympathetic control, although significant, was not close (r = 0.61). The relationship was not affected by beta-adrenergic blockade (r = 0.63). The strength of the correlation improved when multiple regression of respiratory sinus arrhythmia was performed on three variables: parasympathetic control, respiratory cycle length and tidal volume (R = 0.93). 6. It is concluded that in conscious human subjects the respiratory modulation of cardiac parasympathetic activity is different from that observed in the anaesthetized dog, and that variations in the amplitude of respiratory sinus arrhythmia do not necessarily reflect proportional changes in cardiac parasympathetic control.

Adolescent↗
PubMed1989

Cardiac vagal and sympathetic nerve responses to baroreceptor stimulation in the dog.

The effects of ascending stepwise pressure changes in the isolated carotid sinuses on cardiac vagal and sympathetic nerve activities were studied in anesthetized, open chest dogs. The steady state responses of the cardiac vagal and the sympathetic nerve activity and arterial blood pressure were plotted against the sinus pressure and the relations were approximated by the normal distribution function (response curve). The sinus pressure- vs. "reflex gain" relations (reflex gain curve) were approximated by the normal density function. The maximum gain and the "range of change" were found to be greater for the vagal than for the sympathetic and arterial pressure responses. The sinus pressure values derived from "response curves" and "reflex gain curves" for vagal and sympathetic nerve responses were close to each other, while these values and those obtained from arterial pressure responses were considerably apart. It was concluded that: (1) The cardiac vagal neurons are more sensitive to the baroreceptor input than the sympathetic neurons; (2) The similar type of baroreceptor afferent inputs reach the cardiac vagal and the sympathetic structures which are controlling the autonomic outflows.

Animals↗
PubMed1988

Reduced cardiac vagal excitability in hyperthyroidism.

A great deal of uncertainty persists regarding the exact nature of the interaction between autonomic nervous activity and thyroid hormones in the control of heart rate. In the present work we investigated whether reduced vagal influence could contribute to the tachycardia in hyperthyroidism. Vagal excitability was studied in ten hyperthyroid patients. Prolongation of R-R interval in response to carotid baroreceptor stimulation by neck suction was found to be less in the hyperthyroid state compared to the control state after therapy. The extent of nocturnal bradycardia and the vagal excitatory response to the central effect of low dose atropin was significantly reduced in hyperthyroid patients compared to euthyroid controls. We concluded that in the hyperthyroid state cardiac vagal motoneurones were in low excitability state, and speculated that the inhibition might have resulted from thyroid hormone action on CNS structures integrating autonomic function and behaviour.

Adult↗
PubMed1983

Responses in cutaneous vascular tone to transient hypoxia in man.

The study was undertaken to determine the changes in skin circulation in response to systemic hypoxia. Transient hypoxia was induced in 24 healthy subjects by breathing 8% O2 in N2 for 90 s. Arterial oxygen tension was measured transcutaneously (tcpO2), photoplethysmography was employed to monitor changes in cutaneous vessel tone, and respiratory tidal volumes were measured by a Fleisch pneumotachograph. End tidal CO2 concentration, ECG, heart rate, finger skin resistance, and finger skin temperature were monitored continuously as well. Multi-unit skin sympathetic activity was recorded in the median nerve at wrist level by using Tungsten microelectrodes. By the end of the 90 s hypoxic test period tcpO2 was reduced from the control value of 95 +/- 1.8 mm Hg to 51.7 +/- 2.8 mm Hg; respiratory tidal volume increased from the resting value of 585 +/- 22 ml to 746 +/- 38 ml, while photoplethysmographic pulse amplitude decreased to 60% of control, together with a 0.22 +/- 0.03 degree C drop in skin temperature. The values are +/- S.E. In half of the cases skin resistance was reduced as well. Skin sympathetic activity increased during hypoxia and each major burst was followed by a reduction in pulse amplitude. The respiratory and photoplethysmographic responses exhibited similar time courses, with corresponding peaks. Voluntary hyperventilation for 90 s with room air also produced an initial reduction in pulse amplitude; however, it recovered within 60 s. It is concluded that in conscious human subjects, transient systemic hypoxia leads to constriction of cutaneous vessels in the hand, and that the vasoconstriction is the result of increased traffic in sympathetic efferent fibers. Skin vasoconstriction can develop independently of respiratory changes; usually the concomitant hyperventilation facilitates the cutaneous response.

Adult↗
PubMed1982

Functional significance of coactivation of vagal and sympathetic cardiac nerves.

Simultaneous recording of activity in the vagal and sympathetic supplies to the heart has revealed that in reflexly and centrally evoked activity these two "antagonists" do not necessarily change action reciprocally. Coactivation occurs in chemoreceptor reflexes and related reactions, upon stretching of the sinoatrial nodal region of the right atrium and when certain hypothalamic regions are stimulated. The objective of the present work was to assay the physiological importance of coactivation of the two potentially antagonistic cardiac nerves in anesthetized dogs. Output from the heart was monitored by recording volume flow in the thoracic aorta just below the aortic arch; cardiac contractility was measured as left ventricular dp/dt. Tape recordings of vagus and sympathetic nerve activity during chemoreceptor and baroreceptor reflexes, during reciprocal and nonreciprocal changes produced by hypothalamic stimulation, and during hypoxia and hypercapnia were used to trigger stimulators feeding a stimulus per action potential to cardiac vagus and sympathetic nerves after central connections were cut. The vagus stimulation alone produced a decrease in aortic blood flow; stimulation of the sympathetic nerve alone resulted in increased aortic blood flow. Simultaneous stimulation of vagus and sympathetic, however, produced an even greater cardiac output (measured by aortic blood flow). Intermediate degrees of heart rate and strength of myocardial contraction were maintained in coactivation. Obviously, an association of increased vagus and sympathetic actions, which can be effected reflexly or by action of higher centers, is of physiological benefit. In control reactions that relate cardiac function to body need, both reciprocal and synergistic actions (coactivation) of cardiac nerves are used.

Animals↗
PubMed1981

Control of reciprocal and non-reciprocal action of vagal and sympathetic efferents: study of centrally induced reactions.

The mechanism of control of reciprocal and non-reciprocal action between parasympathetic and sympathetic nerves was investigated. Simultaneous recordings were made from both vagal and sympathetic nerves innervating the heart of responses evoked by hypothalamic stimulation in chloralose-anesthetized dogs. Four patterns of responses could be elicited by repetitive stimulations of various sites within the hypothalamus: (1) A reciprocal pattern of cardiac vagal and sympathetic discharges accompanied by a rise in blood pressure, heart rate and a 2 to 8-fold increase in muscle blood flow. The vagal activity completely ceased, while sympathetic discharges were greatly augmented. These changes occurred quickly and often lasted throughout the stimulation, preventing baroreceptor reflex from breaking through. This pattern is similar to the cardiovascular component of the "defense reaction". (2) A reciprocal pattern of discharges accompanied by a depressor response and bradycardia; the vagal discharges increased while those of the sympathetic efferents decreased. (3) A non-reciprocal pattern of response in which activity of the two efferents increased. The blood pressure was elevated and heart rate decreased. (4) A non-reciprocal pattern of action of the two efferents in which discharges of both nerves were depressed; the blood pressure decreased and heart rate increased. Factors affecting these responses patterns were found to be: (a) secondarily occurring reflex responses due to baroreceptor activation or deactivation. These baroreceptor-related reactions always showed reciprocal changes between vagal and sympathetic nerve activity; (b) the level of tonic activity of the autonomic nerves, e.g. during a high level of tonic activity inhibitory action became less effective while the excitatory effect was greater. Thus central states maintaining influenced the pattern of reaction and the relationship between activity in these two efferent nerves. Single pulse stimulations of the hypothalamic regions from which different patterns were evoked, when stimulated repetitively, yielded patterns which were basically reciprocal and biphasic; in vagus efferents an inhibitory phase was followed by an excitation of tonic activity, while in sympathetic an excitation was followed by an inhibition. The degree and duration of these excitatory and inhibitory phases differed, depending on the site of stimulation, but only to a minor degree, and the basic pattern remained unchanged. The implication of these findings is that the hypothalamus can organized both reciprocal and non-reciprocal patterns of activity in the two autonomic limbs in response to varied afferent stimuli. Probably only subtle changes in the central states or influences on neurons of the autonomic system suffice to result in different response pattern. No pattern of response is fixed within the central control complex.

Animals↗
PubMed1981

Cardiovascular reflexes and interrelationships between sympathetic and parasympathetic activity.

Simultaneous recordings from vagal and sympathetic nerve fibers innervating the heart have enabled us to study relationships between activity in these two autonomic nerves. Our recent studies, as well as those of others, are reviewed with respect to tonic activity and reflex actions in these two autonomic efferents. Discharges of the two nerves in relation to blood pressure pulses and to respiratory cycles are reciprocal. During slower fluctuations of hemodynamic changes which occur spontaneously, such as during Mayer waves, a reciprocal relationship between activity in the two autonomic nerves is also observed. On the other hand, in reflex responses both reciprocal and non-reciprocal patterns of reactions produced by stimulations of the hypothalamus showed varied relationships between responses in the two autonomic outflows. The functional significance of the interrelationships of the activity pattern observed in vagal and sympathetic nerves is discussed with respect to control of cardiac functions.

Animals↗
PubMed1980

The mechanisms of differential control in the sympathetic system studied by hypothalamic stimulation.

In an attempt to study the mechanisms of differential action observed in the autonomic nervous system, response patterns evoked in two sympathetic nerves by stimulation of the hypothalamus were investigated. Recordings were made from inferior cardiac and vertebral nerves (mainly vasoconstrictors of the forearm muscles), both originating from stellate ganglia, in chloralose anesthetized cats. Repetitive stimulation of various hypothalamic regions produced 4 types of responses often in single preparations: (1) a response in which differential action between cardiac and vertebral nerves was characterized by an increase in vertebral nerve activity and a decrease in cardiac nerve discharges; (2) a response in which the activities of these two nerves were opposite to that described above; (3) a generalized response of the two nerves; both vertebral and cardiac nerve activity being greatly augmented. This response was accompanied by a great increase in forearm blood flow and could be classified as a part of "defense reaction"; and (4) another type of generalized response in which augmented activity of both nerves was accompanied by a decrease in muscle blood flow. Stimulation of the same hypothalamic area with a single or a short train of pulses evoked in sympathetic neurons an excitation of a short duration, followed by a long-lasting "silent period". The magnitude and duration of these two phases of responses of cardiac and vertebral nerves differed, depending on the site of stimulation. Stimulation of certain hypothalamic points could affect discharges of the left and the right cardiac nerves differently in some animals. The mechanism of differential control in the sympathetic system and some conditions which alter this pattern was discussed.

Animals↗
PubMed1979

Reciprocal and non-reciprocal action of the vagal and sympathetic nerves innervating the heart.

Simultaneous recordings were made from vagal and sympathetic fibers innervating the heart in dogs anesthetized with chloralose. Reciprocal relationship between the two autonomic nerves was clearly seen in the baroreceptor reflex. Stimulation of chemoreceptors, however, evoked non-reciprocal responses of the two nerves; at the onset of the chemoreceptor reflex cardiac vagal and sympathetic discharges both increased, then, as baroreceptors became excited due to a pressor response, sympathetic nerve activity suddenly decreased while vagal discharges remained high, indicating the appearance of the reciprocal action typifying the baroreceptor reflex. Decrease in ventilatory volume and a slight increase in end-expired CO2 level augmented greatly both vagal and sympathetic discharges. As the phrenic-locked activity of the two nerves (i.e. the activity in vagus nerve occurs only in the absence of phrenic bursts while sympathetic discharges increase with phrenic bursts) increased, the alternate discharges between the two nerves became more conspicuous and the heart rate fluctuated with the respiratory (phrenic) rhythm. Thus, strong reciprocity between vagus and sympathetic can result in an oscillatory heart rate. When ventilatory volume was increased, both nerve activities decreased below control level. Mild hypoxia had similar effects to hypercapnia though changes in nerve activity were greater. When coactivation of vagal and sympathetic nerve was produced in reflex action, changes in vagal discharges occurred earlier and faster than in the sympathetic fibers. The magnitude of change in vagus activity was also far greater. The elimination of afferents in the vagi, the aortic and sinus nerves reduced cardiac vagal activity greatly. However, discharges were still present and occurred between phrenic bursts, indicating that the vagal "tone" is maintained centrally as well as peripherally by input from receptors in the cardiovascular system. The physiological significance of reciprocal and non-reciprocal control of vagal and sympathetic nerves innervating the heart was discussed.

Animals↗
PubMed1978

Study of cardiac sympathetic and vagal efferent activity during reflex responses produced by stretch of the atria.

(1) In chloralose anesthetized dogs, effects of the left and the right atrial stretch were studied in the same animal. Stretch of the sino-atrial region of the right atrium produced acceleration of the heart rate during, and reversal of response at the termination of, the stretch. Stretch of the left pulmonary vein-atrial junctional region evoked an initial decrease followed by an increase in heart rate. The responses were similar in all animals, despite initial heart rates ranging from 120 to 200 beats per minute. (2) Activity in vagal and sympathetic nerve branches innervating the heart was recorded simultaneously. Care was taken to identify the vagal fibers innervating the heart, and record their activity without contamination of sympathetic impulses. The right atrial stretch evoked an augmentation of sympathetic activity which reached its peak at 20 sec after the beginning of stimulus. The stimulus slightly increased the vagal activity; this change occurred slowly and reached its peak in about 40-60 sec after stretch. At the release of stretch, sympathetic activity generally showed a reversal of response, i.e. activity was inhibited for 30 sec. (3) Stretch of the left atrium produced biphasic changes in cardiac sympathetic nerves; their activity was strongly inhibited for the first 15 sec, then augmented throughout the remainder of the stretch. This effect lasted 30 sec after the cessation of stimulus. Effects on vagal cardiac nerve fibers were smaller; mild augmentation in activity was produced. The onset of this effect was faster than that seen in case of the right atrium stretch. (4) Reciprocal action between vagal and sympathetic cardiac nerves was obvious only in the early phase of left atrium stretch. Effects on the heart were determined by balances in activity of these antagonistic nerves. In contrast with what occurred in cardiac reflexes, carotid sinus distension even in the same animal produced a large increase in vagal activity, and near complete inhibition of sympathetic nerve activity. Thus, good reciprocal action between the two sets of nerves was demonstrated. A difference in the two types of reflexes was thus revealed. (5) Stretch of the right atrium evoked during carotid sinus distension caused an increase in heart rate from the new low level which was produced by baroreceptor activation. Vagal activity which was greatly augmented by sinus distension was decreased by atrial stretch, while previously inhibited sympathetic activity due to sinus distension was augmented by stretch of the atrium. The effect of stretch on vagal activity seems to depend to a degree on the prestimulus level. It is of interest that the powerful baroreceptor reflexes do not mask the cardiac reflexes studied. (6) The relative importance of sympathetic and vagal efferents to atrial stretch reflexes was discussed.

Animals↗
PubMed1978

Nature of differential sympathetic discharges in chemoreceptor reflexes.

In a study of autonomic reflexes it was found that some produce a generalized, bilaterally uniform response whereas others have an asymmetric or laterality of action. Recordings from vertebral nerve fibers (mainly vasoconstrictors to forelimb muscles), right and left cardiac sympathetics, and renal nerves show that baroreceptors evoke a bilaterally uniform inhibition but chemoreceptors of the carotid sinus and aortic arch initiate a differential discharge. In the chemoreceptor reflex the vagi are activated and bradycardia generally occurs. Vertebral and renal sympathetic fibers increase their activity bilaterally commensurate with the increase in arterial pressure. Sympathetic discharges to the heart, however, are not uniform; they show ipsilateral inhibition and a strong contralateral increase in activity. Stabilization of blood pressure or inactivation of baroreceptors abolishes the ipsilateral inhibition. In isolation, therefore, the chemoreceptor-induced cardiac sympathetic discharge is just quantitatively stronger contralaterally. In the absence of vagi, heart rate changes differ depending on which chemoreceptors are stimulated, because the pacemaker is on the right. Asymmetrical discharges do occur and, in the eventual response to stimulation of chemoreceptors, reflex interactions actually augment the laterality of effects. Peripheral interactions, in the sense that changes effected by one may induce another reflex, are responsible in part for the balances of autonomic activity ultimately seen as the body reacts to stimuli.

Animals↗