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Biomedical subjects

H L Stone

Publications and source records attributed to H L Stone.

At least 55 records · Page 3Linked to original sources
PubMed1982

The effects of horizontal body casting on blood volume, drug responsiveness, and +Gz tolerance in the Rhesus monkey.

To simulate the weightless condition, eight rhesus monkeys, instrumented with solid-state pressure transducers, were horizontally restrained in body casts for 28 d. Blood volume decreased an average of 13% after 14 d of restraint, due mainly to a drop in plasma volume. Aortic pressure and heart rate responses to norepinephrine and phenylephrine decreased after 14 d of restraint. The monkeys did not show a statistically significant decreased tolerance to a 90 degree sudden upright tilt after horizontal restraint. During the fifth week of casting, four animals were subjected to +Gz acceleration tests on a centrifuge. The acceleration tolerance of the casted monkeys was significantly reduced compared to four similarly instrumented control animals. These findings indicate that the cardiovascular deconditioning associated with simulated weightlessness results from an inability to maintain central blood volume during orthostatic stress.

Acceleration↗
PubMed1981

Effects of central venous blood volume shifts on arterial baroreflex control of heart rate.

The purpose of this study was to investigate the effects of anesthesia, body position, and blood volume expansion on baroreflex control of heart rate. Five male rhesus monkeys (7.0-10.5 kg) were given bolus injection of 4.0 micrograms/kg phenylephrine during each of the following situations: awake sitting, anesthetized (AN) (10 mg/kg ketamine-HCl) sitting, AN recumbent, AN 90 degrees head down tilt, and AN 50% blood volume expansion with normal saline. beta-Receptor blockade was also performed on each treatment after anesthesia. Four additional animals were similarly treated after 20% blood volume expansion. R-R interval was plotted against systolic aortic pressure, and the slope was determined by linear regression. Baroreflex slope was significantly (P less than 0.05) reduced by 90 degrees head down tilt and 50% volume expansion both before and after beta-receptor blockade. A similar trend was seen after 20% volume expansion. These data are consistent with the thesis that baroreflex control of heart rate is reduced by central blood volume shifts.

Anesthesia↗
PubMed1981

Coronary blood flow and myocardial oxygen consumption after alpha adrenergic blockade during submaximal exercise.

The presence of a tonic coronary vasoconstriction mediated by the sympathetic nervous system has been demonstrated in conscious and anesthetized dogs during resting and hyperemic conditions. This vasoconstrictor tone could be eliminated by removing the left stellate ganglion and by alpha adrenergic blockade. This study examined the role of alpha receptors on coronary blood flow (CBF) in dogs during submaximal exercise. Eight does were chronically instrumented to measure CBF and left ventricular pressure. Six additional dogs were instrumented to record arterial blood pressure and measure myocardial oxygen consumption. Three weeks later, the dogs were submaximally exercised with or without phentolamine (1 mg/kg i.v.). At a workload of 6.4 km/hr, 16% treadmill elevation, heart rate (HR) increased from a resting level of 95 +/- 2 to 206 +/- 9 beats/min, CBF increased from 28 +/- 2 to 50 +/- 3 cm/sec and dP/dtmax increased from 3775 +/- 333 to 6811 +/- 859 mm Hg/sec. Alpha blockade increased resting HR to 136 +/- 16 beats/min (P less than .05). After alpha blockade, HR was 275 +/- 13 beats/min (P less than .01), CBF was 71 +/- 5 cm/sec (P less than .02) and dP/dtmax was 9419 +/- 856 mm Hg/sec (P less than .05) at a workload of 6.4 km/hr, 16% incline. The response of mean arterial pressure was similar except at the highest workload, when blood pressure was significantly lower with alpha blockade. Myocardial oxygen consumption increased from 3.93 +/- 0.24 to 11.06 +/- 1.63 ml/min before blockade and from 4.14 +/- 0.49 to 15.21 +/- 2.24 ml/min after alpha receptor blockade. The increase in coronary flow in these dogs was greater for any given oxygen demand. The effect of phentolamine was, therefore, independent of the higher HR and dP/dtmax. During exercise, the greater increase of CBF after alpha blockade suggests the removal of a neurally mediated vasoconstrictor tone which was still present during submaximal exercise and which may be independent of normal metabolic demands of the myocardium.

Adrenergic alpha-Antagonists↗
PubMed1980

Interaction of fastigial pressure response and depressor response to nasal perfusion.

The fastigial nucleus pressor response (FPR) and the nasal-perfusion diving response were elicited alone and simultaneously to observe the net effect on cardiovascular variables. The fastigial nucleus was electrically stimulated in 14-chloralose-urethane anesthetized dogs and the FPR was characterized by a transient tachycardia with sustained elevations in arterial pressure, left ventricular pressure and maximal dP/dt. The tachycardia was buffered by baroreceptor reflexes during the elevated arterial pressure of the FPR. All variable of the FPR, however, were reduced by superimposition of the diving response upon the FPR. Heart rate was most sensitive to depression by the nasal perfusion which elicited a bradycardia as much as 70 beats/min below the control rate. The nasal-evoked diving response was discussed with respect to the trigeminal depressor response which results from direct stimulation of the spinal trigeminal complex. Algebraic cancellation of the FPR and dive responses is considered along with anatomical and electrophysiological evidence which suggests that these two responses, as well as the baroreceptor reflex, could be integrated at a common site. This site may be the medullary nucleus of the solitary tract which receives projections from trigeminal and glossopharyngeal nerves and from the fastigial nucleus.

Adrenergic Fibers↗
PubMed1980

Coronary flow, myocardial oxygen consumption, and exercise training in dogs.

Changes in coronary blood flow (CBF) and myocardial oxygen consumption (MVO2) were measured in 17 conscious dogs during submaximal exercise and before and after exercise training. The CBF responses to atrial pacing and a 10-s occlusion were measured in the resting animals. With atrial pacing at 240 beats/min, the change in CBF from resting values increased significantly (12.8 +/- 1 to 15.2 +/- 3 cm/s), reactive hyperemia response was decreased (463 +/- 55 to 328 +/- 52%), and CBF during submaximal exercise was reduced by the end of the 4th or 5th wk of training. These changes persisted for the duration of the training program. When the animals were trained, the CBF response to submaximal exercise was the same as in the untrained condition. Exercise MVO2 did not change with training, but oxygen extraction increased (80 +/- 1 to 83 +/- 1%). These results indicate that changes in the coronary vascular bed occurred very early in the training program and may be explained by either an autonomic nervous system change in control of coronary flow or a change in the anatomic architecture of the bed.

Animals↗
PubMed1980

Left stellectomy in the prevention of ventricular fibrillation caused by acute myocardial ischemia in conscious dogs with anterior myocardial infarction.

The potential of left stellectomy in reducing the incidence of ventricular fibrillation associated with acute myocardial ischemia was investigated in a new animal model for sudden death. Thirty-two dogs had an anterior myocardial infarction produced by ligation of the left descending coronary artery. One week later they were randomly allocated to a control or to an experimental group that underwent left stellectomy. One month after ligation while the dogs were conscious, a balloon occluder previously positioned around the circumflex coronary artery was inflated and the ensuing coronary occlusion was maintained for 10 minutes. Ventricular fibrillation occurred in 11 of 17 (65%) control dogs, compared with five of 15 (33%) (p < 0.05) in the experimental group. Among the survivors the incidence of arrhythmias was less in the experimental group compared with the control group. Infarct size (21 +/- 2% vs 20 +/- 2%), resting heart rate (143 beats/min vs 127 beats/min) and QTc (347 +/- 11 msec vs 349 +/- 13 msec) were similar between control and experimental groups. The dogs that died had a greater increase in heart rate at 1 minute postocclusion than survivors and also had significantly longer QT intervals. Our study indicates that left stellectomy exerts a major protective effect in reducing the incidence of ventricular fibrillation when conscious dogs with a previous anterior myocardial infarction undergo acute myocardial ischemia. This simple and safe surgical procedure may be considered for a clinical trial in subgroups of patients with ischemic heart disease at very high risk for sudden death.

Animals↗
PubMed1980

Neural control of the heart during arrhythmias and exercise.

Involvement of neural activity during cardiovascular adjustments and during arrhythmias can be determined by comparing the results of cardiovascular changes after lesions are made in nuclei or pathways of the central nervous system or ablations of ganglia or nerves are made in the peripheral nervous system. The neural effects can be exaggerated if these systems are forced to perform at higher levels during a stressful situation. The purpose of this presentation is to discuss the responsiveness of the cardiovascular system after left or right stellate ganglionectomy and after lesions are made in the fastigial nucleus of the cerebellum in dogs stressed with submaximal exercise. These dogs are implanted with instruments that are designed to measure cardiovascular responses. Hypotheses for potential neural mechanisms are generated from the results of chronic animal studies, and these mechanisms are tested in anesthetized dogs and cats. Electrical stimulation of ascending and descending pathways in the central nervous system and stimulations such as coronary occlusion and mechanical probing are used to activate neural mechanisms in the anesthetized state. A general schema concerning the results of our studies provides further information about our approach to understanding the physiological role that the central nervous system may exert on the cardiovascular system during stress.

Afferent Pathways↗
PubMed1979

Model course for retraining inactive medical technologists.

In the belief that there is an ongoing need for the retraining of inactive medical technologists, the University of Wisconsin-Madison initiated such a program in 1978. A model course in routine chemistry and instrumentation was developed, presented, and evaluated. This model is described in detail. Results indicate that most inactive medical technologists can regain competence. The program and individual courses are designed so they can be easily replicated or adapted for use by others interested in retraining inactive medical tehcnologists.

Clinical Competence↗
PubMed1978

Instructional objectives for a teaching program in cancer for primary care physicians.

Precise instructional objectives are critical to the success of educational programs in medicine. Adequate attention to the development of instructional objectives prompts careful consideration of course methods, helps define means of evaluation, and results in realistic long-term goals. Current curricula often focus on the teaching of facts and the diagnosis and treatment of advanced and uncommon diseases; behavioral science skills are rarely taught and, in general, content is unrelated to the kinds of problems physicians see in practice. This paper presents instructional objectives in cancer which attempt to answer these criticisms. The objectives, covering cognitive, psychomotor, and affective domains, emphasize the areas of prevention and early diagnosis.

Family Practice↗
PubMed1977

Functions of selected biochemical systems from the exercised-trained dog heart.

Mitochondria and sarcoplasmic reticulum (SR) fractions were isolated from exercised-trained (E-T) and sedentary control dog hearts. Measurements of mitochondrial respiratory functions indicated no changes in energy-producing (ATP synthesis) capacity in mitochondria from E-T compared to control dog hearts. However, the ability of isolated mitochondria from E-T hearts to retain accumulated calcium was markedly decreased compared to controls. Inhibition of mitochondrial rates of calcium uptake with the inhibitor, ruthenium red, revealed fewer binding and/or transport sites in mitochondrial membranes from exercised-trained heart preparations. ATP-dependent binding (- oxalate) and uptake (+ oxalate) of calcium by SR preparations from E-T hearts were unchanged compared to controls. In contrast, significant differences in the rates of release of bound calcium were found in SR isolated from E-T hearts. Total myocardial protein, nucleic acids, and connective tissue levels were unchanged in E-T hearts compared to controls. The results suggest subtle changes are occurring in the energy-utilizing mechanism(s) involving calcium transport of the myocardial cell during exercise training. These changes may be related to alterations in the performance of the exercised-trained heart.

Animals↗
PubMed1977

Cardiac function and exercise training in conscious dogs.

Exercise training (T) was accomplished in 21 mongrel dogs. The animals were instrumented to measure ascending aortic flow, left ventricular pressure, and left atrial pressure. They were allowed to recover for 4 wk following surgery before accomplishing a standardized submaximal test (SMT). The exercise program alternated daily between sprint and endurance training. During T, the animals were tested while lying quietly on a laboratory table as well as during the SMT. In six animals, ventricular function curves (VFC) were obtained by rapid volume loading at similar time intervals as the SMT. Heart rate increased during the SMT but was found to be reduced in the T animals by an average of 20 beats/min. The maximum derivative of left ventricular pressure (P) increased during the SMT in T animals by an average of 2,200 Torr/s above the untrained animals. The VFC was lower in T animals than untrained animals because of a reduction in heart rate response. Results indicate a reflex adaptation of the nervous system with training to improve cardiac function.

Animals↗