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Biomedical subjects

H L Stone

Publications and source records attributed to H L Stone.

At least 73 records · Page 4Linked to original sources
PubMed1977

Contractile function and myofibrillar ATPase activity in the exercise-trained dog heart.

Myocardial contractility and the enzymatic (ATPase) activity of cardiac contractile proteins were examined after exercise training using the chronically instrumented, unanesthetized dog as an experimental model. Before training, heart rate and the maximum rate of left ventricular pressure development (max dP/dt) were measured at rest and during submaximal exercise. Animals were then subjected to an 8- to 10-wk treadmill running program. Training was verified by the establishment of a 10- to 20-beat/min reduction in heart rate during submaximal exercise. After training max dP/dt was within normal limits at rest, but significantly elevated during submaximal exercise. When max dP/dt was plotted as a function of heart rate, either with the animal standing quietly on the treadmill or during submaximal exercise, a marked elevation in max dP/dt at any given heart rate was observed following training. Myofibrillar protein yield and ATPase activity values were nearly identical in left ventricles from exercise-trained and sedentary control dogs. Although exercise training by treadmill running improved contractile function in the unanesthetized dog myocardium, this response does not appear to involve alterations in myofibrillar ATPase activity.

Adenosine Triphosphatases↗
PubMed1977

The unanesthetized instrumented animal preparation.

The use of the unanesthetized instrumented animal preparation in exercise training studies is discussed. The advantages and disadvantages of this preparation are given. Several examples of the type of data that can be collected using this preparation are cited and a scheme is proposed to aid in the understanding of the mechanisms underlying the cardiac adaptation to exercise training. One example given was the response to the infusion of isoproterenol before and during training. The results clearly demonstrate an increased responsiveness to the beta-receptor agonist. Another example was the change in coronary flow with atrial pacing and the use of this relationship as an index of a changed coronary vascular bed. Some future direction for research efforts are discussed with the main thrust being the role of the autonomic nervous system in the mechanism of training.

Animals↗
PubMed1977

The evaluation of teaching effectiveness: the myths about student ratings.

This study presented to a conceptual framework for gathering and using student ratings to evaluate teaching effectiveness. Within the framework student evaluations of all courses of a second year pathophysiology curriculum were analyzed. Data analyses indicated student evaluations of courses and teaching activities were not related to the grades students received, nor did they varyin relation to the time they were obtained.

Achievement↗
PubMed1977

Factors influencing internship/residency and practice locations: implications for public policy.

This study analyzed the location attachment characteristics of graduates of the University of Wisconsin-Madison Medical School to test three hypotheses describing the relationship of these characteristics to the graduates' choice of internship and practice location. Data analyses revealed no significant relationships between graduates' place of birth and academic performance and their decisions to intern and/or practice in Wisconsin.

Achievement↗
PubMed1976

Effects of unilateral stellate ganglion blockade on the arrhythmias associated with coronary occlusion.

In anesthetized dogs the circumflex and/or the anterior descending coronary artery were briefly occluded (10 to 90 seconds) and ectopic beats occurring during the occlusion or for 60 seconds following release were counted. Control occlusions were alternated with occlusions performed during complete, reversible, unilateral blockade of either the right or the left stellate ganglion. This was achieved with thermodes through which coolant was circulated. In this way the shortcomings associated with stellectomy, which is irreversible, are avoided. Blockade of the right stellate ganglion increased the number of ectopic beats associated with coronary occlusion. The occurrence of episodes of ventricular tachycardia and fibrillation was also greater. By contrast, blockade of the left stellate ganglion reduced or abolished occlusion-induced arrhythmias. These effects are independent of changes in heart rate or vegal activity; they depend solely upon unilateral alteration in sympathetic tone, and are not demonstrable when such tone is low. We suggest that the right and left cardiac sympathetic nerves have a different influence upon cardiac excitability.

Animals↗
PubMed1976

Effect of dorsal root section on the arrhythmias associated with coronary occlusion.

In anesthetized vagotomized dogs and cats the circumflex and/or the anterior descending coronary artery were briefly occluded (5-90 s), and ectopic beats occurring during the occlusion and for 60 s following release were counted. When arrhythmias were regularly produced for a given occlusion, the dorsal roots from C8 to T5 were transected and the occlusions were repeated. Dorsal root section produced minor changes in heart rate and blood pressure. Dogs and cats did not differ in their responses. Dorsal root section was performed in eight animals and decreased the absolute number of ectopic beats by 63 +/- 19% compared to control values (P less than 0.05). In four animals the effect on ectopic beats produced by repeated occlusions without dorsal root section was investigated and found to be increased by 35 +/- 24% compared to contrl values. Most of the somatic afferents contained in the dorsal roots were damaged by the surgical preparation. Therefore, repeated occlusions and interruption of somatic afferents do not appear to have influenced our results. The arrhythmogenic interaction between the local effects of myocardial ischemia and the sympathetic activity, whose outlow contained in the ventral roots remained intact, was still possible after dorsal root section and this explains why ectopic beats were reduced but not almost suppressed as is usually the case after bilateral stellectomy. We conclude that dorsal root section reduces the number of ectopic beats associated with short-lasting coronary artery occlusions and that the most likely mechanism is the interruption of the cardiocardiac sympathetic reflex which depends upon afferent fibers running through the dorsal roots.

Animals↗
PubMed1976

Automic innervation of dog coronary arteries.

The autonomic innervation of canine coronary arteries has been examined using the Falck and Owman technique for demonstrating catecholamines and a modification of the Koelle technique for the demonstration of cholinesterase. The experimental protocol included an examination of the neural innervation of the major coronary arteries: LCC, LAD, and RCA. A consistent, relatively dense adrenergic innervation was noted. A gradient in the degree of cholinergic innervation was: LAD less than RCA less than LCC. Light microscopic examination of the hearts of dogs subjected to either cervical vagotomy or total extrinsic cardiac denervation was performed. Additional surgical procedures included removal of the left stellate ganglion and a preferential stripping of the LCC. These studies demonstrated the intrinsic nature of parasympathetic coronary innervation. Following all surgical procedure no variations in density of cholinergic innervation were noted, indicating that these fibers are probably postganglionic parasympathetic fibers arising from intrinsic ganglia within the ventricles. These ganglia may be located at the base of the great vessels and send their fibers to the coronary vessels via the septal artery.

Animals↗
PubMed1976

Cerebellar pressor response in the dog.

A fastigial pressor response has been elicited in the anesthetized mongrel dog. Stimulation within the rostral portions of this nucleus results in mean arterial pressure rises up to 150 mmHg above control. A proportional tachycardia is simultaneously evoked which may rapidly attain heart rates of 190 beats/min above control levels. Peak tachycardias immediately suside and often the heart rate declines below control values during stimulation while arterial pressure remains elevated. When either the carotid sinuses were isolated by ligation or a bilateral vagotomy was performed, the fastigial tachycardia was sustained. Thresholds for the response are near 0.05 mA and the stimulus intensity curve is linear to 0.4 mA whereupon the pressure rise and tachycardia begin to approach a plateau value. The response could still be attained when submaximal doses of alpha-chloralose anesthesia or high levels of barbiturates (30-40 mg/kg) were given. Both portions of the response result from widespread sympathetic activation; however, buffering of the response through the baroreceptor reflexes is only demonstrated in the cardiac segment of the response.

Animals↗
PubMed1976

Effect of a reduction in arterial oxygen content (carbon monoxide) on coronary flow.

Mongrel dogs were chronically instrumented for ventricular pacing, to measure left circumflex coronary flow (CF), left ventricular and arterial pressure, and to obtain blood samples from the left atrium and coronary sinus. Following a 3- to 4-week recovery period, the animals were subjected to a 30% reduction in arterial oxygen saturation by exposure to low levels of carbon monoxide. Three types of experiments were performed: 1) control, 2) pacing at 150 bpm, and 3) double blockade with propranolol and atropine. Reduction in arterial oxygen saturation in the three conditions studied resulted in a significant increase in CF and no change in myocardial oxygen consumption. The relationship between CF and arterial saturation demonstrated that double blockade produced a difference in the magnitude of the CF response. These results indicate a neurogenic mechanism to regulate coronary flow that may aid in maintaining oxygen availability during stressful conditions.

Animals↗
PubMed1976

Ultrastructural effects of +Gz stress on swine cardiac muscle.

Miniature swine were subjected to 9 +Gz acceleration for 60-120s. Within 2 h following the +Gz force, the anterior papillary muscle was removed and prepared for scanning and electron microscopy. Ultrastructural changes observed in the cardiac myocytes included cellular redistribution of mitochondria and nuclei. Tears in the contractile fibers, bizarre profiles or nuclei, and peculiar membrane-bounded bodies in the cytoplasm also were observed. Hemorrhagic areas were localized around the Purkinje fibers. The T system and plasma membrane appeared unperturbed. The conclusion was drawn that, following high +Gz levels of acceleration, damage to myocardial ultrastructure ensues.

Acceleration↗
PubMed1976

Cardiovascular function during sustained +Gz stress.

The development of aerospace systems capable of very high levels of positive (+Gz) stress, has created a need for a better understanding of the cardiovascular responses to acceleration. Using a canine model, the heart and cardiovascular system were instrumented to continuously measure coronary blood flow, cardiac output, left ventricular and aortic root pressure, and oxygen saturation in the aorta, coronary sinus, and right ventricle. The animals were exposed to acceleration profiles up to +6 Gz, 120 s at peak G; a seatback angle of 45 degrees was simulated in some experiments. Radiopaque contrast medium was injected to visualize the left ventricular chamber, coronary vasculature, aorta, and branches of the aorta. The results suggest mechanisms responsible for arrhythmias which may occur, and subendocardial hemorrhage which has been reported in other animals.

Blood Pressure↗
PubMed1975

Effect of heart rate on left atrial systolic shortening in the dog.

The relationship between heart rate and left atrial end-diastolic diameter (LAEDD) and left atrial systolic shortening (LASS) was investigated in 12 conscious dogs. Atrial pacing, vagal blockade, isoproterenol, and beta-adrenergic blockade were used to change heart rate and the inotropic state of the atrium. LAEDD decreased linearly as heart rate increased. LAEDD averaged 33.0 mm (+/- 0.6 mm SEM) and decreased by 3.2 mm (+/- 0.4 mm SEM) with a change in heart rate of 50 beats/min. The ratio of LASS/LAEDD decreased as LAEDD decreased with increasing heart rate, but there was less of a reduction in the ratio at the extreme levels of LAEDD change with isoproterenol and vagal blockade. Propranolol reduced LASS at any LAEDD. At lower heart rates the reduction of LASS with pacing could be corrected by returning LAEDD to near control levels with a rapid infusion of fluid. It is concluded that LASS is primarily dependent on LAEDD and the inotropic state of the atrium. At higher heart rates, though, some effect of frequency can be observed. Isoproterenol and vagal blockade (increased contractile state) reduced the dependence of LASS on LAEDD.

Animals↗
PubMed1975

Heart biochemical responses in miniature swine subjected to +Gz acceleration.

Myocardial biochemical systems which are sensitive to hypoxic and ischemic insult were studied to determine the possible etiology of ventricular endocardial hemorrhage in miniature swine following +GZ stress. Unanesthetized animals were subjected to a single, 120-s +9 GZ acceleration. Approximately 1-2 h following +GZ exposure, the animals were anesthetized and the hearts removed for analyses. Acceleration exposure resulted in the loss of acid phosphatase enzyme activity from the membrane-bound lysosomal fraction with concomitant increased activity in the soluble fraction. This suggests that lysosomal membrane integrity had been disrupted. Mitochondrial preparations from +GZ-stressed hearts exhibited marked increases in active respiratory rate and rate of calcium transport while oxidative phosphorylation efficiency was unchanged. The results clearly indicate that +GZ acceleration is capable of altering myocardial biochemical systems. However, the results tend to suggest that these alterations in cellular processes may be mediated by influences other than hypoxia or ischemia.

Acid Phosphatase↗
PubMed1974

Cardiac responses to snout immersion in trained dogs.

1. Four dogs were trained to immerse their snout voluntarily for durations up to 30 sec. Indwelling instrumentation was implanted to measure blood flow velocity in the circumflex branch of the left coronary artery, to sample blood from the left atrium and coronary sinus for the determination of P(O2), P(CO2), pH, oxygen saturation and haemoglobin concentration, and to pace the heart. An index of myocardial oxygen consumption was calculated by multiplying the mean flow velocity by the arteriovenous difference in oxygen content.2. Mean coronary flow velocity decreased significantly during simulated diving by 26 +/- 27% (+/- S.D.). The range of decrease in seventeen out of twenty experiments was from -5 to -81%. Heart rate decreased by 48 +/- 7% and this bradycardia was abolished by I.V. atropine.3. Coronary sinus oxygen saturation increased significantly with snout immersion (three dogs) and arteriovenous difference decreased from 67 +/- 10 to 47 +/- 5%. The index of myocardial oxygen consumption decreased by 42 +/- 19%. This decrease was attenuated slightly by beta-blockade but was abolished by cardiac pacing in three out of four experiments.4. The present study indicates that the heart consumes oxygen at a considerably reduced rate during simulated diving and therefore plays a direct role in the overall conservation of oxygen. This response appears to result primarily from a negative chronotropic effect induced by increased vagal tone.

Animals↗