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Biomedical subjects

W C Randall

Publications and source records attributed to W C Randall.

At least 127 records · Page 7Linked to original sources
PubMed1978

Comparison of SA nodal and subsidiary atrial pacemaker function and location in the dog.

A 3-4 cm length of sulcus terminalis tissue including the sinoatrial node (SAN) was excised from 14 dogs. After an initial junctional rhythm with SAN excision a P wave emerged within days to weeks in 12 animals. Maximum heart rates of the SAN (preoperative) in response to exercise (276 +/- 15 beats/min), isoproterenol infusion in conscious animals (272 +/- 11 beats/min), and stellate stimulation during anesthesia (273 +/- 9 beats/min) were significantly greater than subsidiary pacemakers (postoperatively) for exercise (219 +/- 9 beats/min), isoproterenol (226 +/- 8 beats/min), and stellate stimulation (197 +/- 9 beats/min). During a final experiment, electrophysiological mapping of the area of earliest epicardial activation (pacemaker location) was carried out. By use of a suction electrode in reference to plunge electrodes located in the anterior interatrial band (AIB), eustachian ridge of the coronary sinus, and limbus of the fossa ovalis, the pacemaker was located at the inferior vena cava-inferior right atrial junction in 80% of the animals mapped. During isoproterenol infusion the foci shifted to regions of the AIB in 70% of the animals mapped. The concept of pacemaker hierarchy is discussed.

Animals↗
PubMed1977

Responses of the canine myocardium to stimulation of thoracic cardiac nerves.

The thoracic cardiac nerves were stimulated in each of 21 dogs anesthetized with alpha chloralose. Recordings were made of heart rate, blood pressure, and contractile force from all four cardiac chambers. Walton-Brodie strain-gauge arches were sutured to both atria, and to three locations of each ventricle, representing both anterior and posterior surfaces. The functional autonomic components of each nerve were summarized and classified into four basic types. Types I and II were both located medial to the thoracic vagi. These were shown to contain both sympathetic and parasympathetic components traveling to all four chambers of the heart. The sympathetic componnent of the type II nerves produced reflex changes in force of contraction and systemic blood pressure. Nerves classified as types III and IV produced no parasympathetic effect on the heart. These were all located lateral to the thoracic vagi. While the type III nerves carried sympathetic efferent fibers to all four chambers, the type IV nerve carried sympathetic fibers predominantly to the right atrium.

Animals↗
PubMed1977

Chronology and mode of reinnervation of the surgically denervated canine heart: functional and chemical correlates.

This study was undertaken to evaluate functionally the time and pattern of inotropic and chronotropic efferent cardiac reinnervation of the deneravated canine heart and to correlate functional data with regional myocardial catecholamine content and supersensitivity to norepinephrine. Our data indicate that efferent autonomic reinnervation takes place first in the atria, followed by a base-to-apex sequence in the ventricles, and that such reinnervation is functionally effective 9-12 mo after denervation. The return of neural function parallels the return of measurable quantities of myocardial norepinephrine and is accompanied by a decrease in supersensitivity to exogenous norepinephrine. The return to apparently complete functional reinnervation, however, cannot be quantitatively related to myocardial levels of catecholamine. Segmental myocardial supersensitivity to norepinephrine is sequentially reversed during progressive adrenergic reinnervation.

Adrenergic Fibers↗
PubMed1976

Cardiac dysrhythmias in the conscious dog after surgically induced autonomic imbalance.

The ventrolateral cardiac nerve in the dog is a primary branch of the left sympathetics and represents a direct neural link between the central nervous system and the heart. Its electric excitation elicits characteristic shifts in pacemaker and tachydysrhythmias related to its explicit innervation of the inferior atrial, atrioventricular (A-V) junctional and ventricular tissues. Total denervation of the canine heart, sparing the ventrolateral cardiac nerve, produced a long-term model in which only these portions of the heart retained their sympathetic innervation. The trained unanesthetized model dog was subjected to severe exercise in order to determine the effects of elevated levels of sympathetic tone upon these important regions of the conduction system. Reproducible tachydysrhythmias were elicited in all six animals completing the regimen of periodic testing over a period of 136 to 378 days after operation. The abnormal rhythms consisted of shifting cardiac pacemakers and supraventricular A-V junctional and ventricular tachycardias with frequent premature systoles. Comparable abnormalities were not observed in a similarly tested sham-operated animal or in dogs with a totally denervated heart. The exercise-induced dysrhythmias gradually disappeared with time, presumably in relation to autonomic reinnervation of the heart. The characteristic patterns of ventrolateral cardiac nerve and upon its presumed influence upon Purkinje fiber and A-V nodal automaticity and temporal dispersion of refractoriness in myocardial tissues.

Animals↗
PubMed1976

Response of primate heart to emotional stress before and after cardiac denervation.

Eleven chair-restrained rhesus monkeys were classically conditioned to a 1-min, 900-Hz tone (CSf) followed by food and a 1-min, 3.4-5Hz tone (CSs) followed by shock. Each conditional stimulus produced large, sudden, and highly significant (P less than .01) increases in left ventricular systolic pressure (LVP), its first time derivative (d(LVP)/dt), and heart rate (HR). The animal's hearts were sugically denervated following control studies of the conditional responses. Two to four weeks later, these responses were reexamined by again presenting CSf and CSs to five surviving monkeys following a format identical to that used in the control experiments. Complete cardiac denervation virtually eliminated the sudden increases in each of the measured variables. Denervation also "unmasked" small-magnitude, delayed chronotropic and inotropic responses during CSs (but not CSf). These effects were ascribed to the action of circulating catecholamines known to be secreted during "emotional" stress. Four monkeys studied for 6 mo or more postoperatively showed evidence for varying degrees of cardiac reinnervation. Loss of nervous control of the nonhuman primate heart greatly compromises the cardiovascular response to these environmental and behavioral stress situations.

Animals↗
PubMed1976

Autonomic neural control of cardiac rhythm: the role of autonomic imbalance in the genesis of cardiac dysrhythmia.

Cardiac dysrhythmias result from abnormalities in rate, regularity, or sequence of cardiac activation, and because of direct actions of the autonomic nervous system upon each of these properties, imbalance in this system may play an important role in the genesis of cardiac dysrhythmia. A canine model has been developed in which the extrinsic innervation of the heart is ablated with the exception of the ventrolateral cardiac nerve. This nerve is distributed primarily to the inferior atrial, AV junctional, and ventricular tissues. Following recovery from surgery, the animal is placed on a treadmill and required to perform strenuous exercise. In all of six animals which sustained repeated exercise testing over periods of 4-12 months, dysrhythmias of varying complexities were elicited. None appeared in parallel experiments conducted in control or sham-operated animals. The dysrhythmias consisted of supraventricular, AV junctional, or ventricular tachycardias with occasional premature atrial or ventricular systoles. The dysrhythmias were not influenced by atropine but were generally controlled by propranolol.

Animals↗
PubMed1975

Direct and reflex cardiac bradydysrhythmias from small vagal nerve stiumaltions.

Alterations in cardiac pacemaker location, its rate of discharge, and A-V conduction patterns were induced in anesthetized adult dogs by electrical stimulation of the thoracic vagi and their small cardiac branches before and after cervical vagotomy. Electrical activity from small, contiguous bipolar silver electrodes was amplified and recorded by an optical oscillograph. The electrodes were located over the SA node, the three internodal pathways, the left atrium, and ventricular epicardium. A hoffman-type plaque electrode was placed over the A-V node to record a His bundle electrogram simultaneously with a Lead II electrocardiogram. Electrical stimulation of the intact left recurrent laryngeal nerve and its cardiac branches before and after vagotomy induced both direct and reflex effects on SA nodal cycle length. Efferent dromotropic effects on the A-V node varied from first- to third-degree heart block during stimulation of individual left recurrent cardiac branches. Stimulation of the right recurrent cardiac nerve induced atrial bradycardia with heart block above the His bundle. Stimulation of individual right vagal branches near the heart induced bradycardia, cardiac asystole, shifts in atrial pacemaker location, or activation of His pacemakers. Establishment of the His rhythm probably indicates selective inhibition of supraventricular but not of the His bundle. Asystole and His rhythms induced during stimulation of the more caudal branches of the right cardiac vagal nerves were generally reflexly mediated and were abolished by cervical vagotomy.

Animals↗
PubMed1975

Localized myocardial responses to stimulation of small cardiac branches of the vagus.

Direct electrical excitation of small cardiac branches from the thoracic vagus elicited highly localized and differential responses from individualized segments of the myocardium. For example, small nerves from the vagus at the level of the superior pulmonary veins frequently induced moderate inhibition in contractile force of the ipsilateral atrium with little or no influences elsewhere. Branches from more rostral levels of the thoracic vagus induced changes in atrial contractility, with or without changes in sinoauricular (SA) nodal discharge rates, and often with partial or complete artioventricular (AV) nodal blockade.Excitation of individual, small vagal branches sometimes initiated acceleration in artrial rate and augmentation in atrial contractile force concurrently with complete AV nodal blockade. The negative dromotropic response was eliminated by atropine, leaving only the positive chronotropic and inotropic changes, thus revealing the intermingling of both sympathetic and parasympathetic components even in these small branches. There are frequently in excess of 20 small branches from the vagal trunk between the level of the caudal cervical ganglion and the superior pulmonary vein on each side which will induce highly selective changes in cardiac function upon stimulation. Inhibitory branches are particularly concentrated in the region of the recurrent laryngeal nerve on either side.

Animals↗
PubMed1975

Cardiovascular responses to bladder distension in patients with spinal transection.

Arterial blood pressure, heart rate, and cutaneous volume pulses were recorded during controlled elevation of urinary bladder pressure in a group of seven patients with spinal cord transsection above vertebral level T5 and in another group of four patients below T5. Profound elevations in systolic blood pressure and pulse pressure were induced by bladder distension when the lesion was situated above T5. Lesser elevations occurred in patients with lesions below T5. Marked vasoconstriction characterized skin areas innervated by the "isolated" spinal cord, while passive dilatation occurred in areas supplied by the proximal cord. Only three of seven patients with lesions above T5 level had decreased heart rate during marked elevations in arterial blood pressure. The marked elevations in pulse pressure in patients with lesions above T5 could not be explained solelyby increased vasoconstriction and decreased heart rate, but involves also inotropic cardiac responses. These inotropic responses are mediated by cardiac sympathetic nerves which leave the spinal cord above the T5 level.

Animals↗
PubMed1975

Selective parasympathectomy of the heart.

Attempts to devise a chronic animal model with parasympathetic cardiac denervation have been complicated by early mortality due to pulmonary and esophagogastric dysfunction. By use of surgical techniques confined to the intrapericardial left atrium and immediately adjacent vena cava, selective cardiac parasympathectomy was performed on dogs. Verification of denervation was performed at the time of surgery by electrical stimulation of the cervical and thoracic vagi and stellate ganglia while recording blood pressure, ECG, and atrial and ventricular contractile force. Results demonstrate complete efferent parasympathetic denervation and abolition of the Bezold-Jurish reflex. Tachycardia at approximately 140/min was noted in all animals immediately and for several weeks postoperatively. No extracardiac complications were noted in any of the animals subjected to this procedure. Right heart catheterization of the conscious sedated dog revealed no evidence of right heart failure. Evidence of parasympathetic efferent reinnervation (sinus arrhythmia) was seen in some animals. This preparation should prove useful in studies of parasympathetic control of the heart, coronary vessels, and cardiovascular reflexes.

Animals↗
PubMed1975

Functional anatomy of canine cardiac nerves.

In 20 anesthetized dogs the thoracic autonomic nerves were carefully exposed in order to determine which produced cardiovascular responses when the afferent or efferent component of each was stimulated. Efferent parasympathetic and sympathetic fibers arise from the caudal cervical ganglion regions bilaterally as well as from the vagus caudally to that ganglion. The majority of negative chromotropic, dromotropic and inotropic fibers arise from the vagus or near the recurrent laryngeal nerves; however, some small parasympathetic fibers also arise from the vagi down to the level of the pulmonary vessels. Efferent sympathetic nerves are relatively large with the exception of the stellate cardiac nerves, and produce specific positive chronotropic or inotropic responses. Afferent fibers are numerous in the recurrent cardiac, innominate, ventromedial and dorsal nerves and not very numerous in both stellate cardiac nerves as well as in the nerves at the level of the pulmonary vessels; thus there are numerous cholinergic and adrenergic efferent fibers which exhibit specific chronotropic or inotropic responses. The correlation between neural anatomy and specific physiological cardiodynamics illustrates beautifully the interrelationship of structure and function which exists within the autonomic nervous system.

Animals↗