摘要:

In the canine isovolumetric left ventricle preparation, stimuli were applied to the efferent end of a transected cervical vagus nerve. The changes in left ventricular systolic pressure in response to vagal stimulation were compared under control conditions and when ventricular contractility was enhanced by various kinds of inotropic stimulation–left stellate ganglion stimulation, paired pacing, calcium chloride infusions, aminophylline infusions, and acetylstrophanthidin injections. Vagal stimulation under control conditions caused mean decreases in pressure in the various groups ranging from 13.2 to 16.2% of the control level. The depressant effect of vagal stimulation was potentiated during sympathetic stimulation, in confirmation of previous findings; the mean decrease in pressure produced by vagal stimulation during concurrent sympathetic stimulation varied from 20.1 to 20.8%. Calcium and aminophylline infusions had no significant effect on the ventricular response to vagal stimulation; the percent reductions in pressure caused by vagal stimulation were 18.1 and 15.5%, respectively. However, the response to vagal stimulation was markedly attenuated during paired pacing and after acetylstrophanthidin; the percent reductions in pressure caused by vagal stimulation were 5.0 and 9.4%, respectively. The potentiation of the response to vagal stimulation during increased cardiac sympathetic activity probably represents a specific adrenergic-cholinergic interaction.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

This investigation was designed to determine whether a defect in energy utilization exists in heart failure. Accordingly, the direct conversion of chemical energy to mechanical work was studied in right ventricular papillary muscles from normal cats and cats with experimental right ventricular failure secondary to pulmonary artery constriction. Energy production was inhibited by iodoacetic acid and N2. After resting or performing variable amounts of internal contractile element work under isometric conditions, muscles were instantly frozen, and the total amount of chemical energy (∼ P = creatine phosphate + ATP) used was correlated with work performed and the number of contractions. The contractile properties of papillary muscles from cats with heart failure were severely depressed. There was a significant depression in initial ∼P stores in muscles from cats with heart failure, but there was no significant change in the resting rate of ∼P utilization. Although the muscles from cats with heart failure performed, on the average, 13% as much work and were activated 64% as many times, the average amount of energy used was only 7% of that used by normal muscles. It is concluded that in this form of experimentally produced heart failure the utilization of ∼P is reduced but only in relation to the reduction in contractile element work and that the direct conversion of chemical energy to mechanical work is not an inefficient process in this state.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Left and right carotid sinus pressures were independently varied while the left ventricular systolic pressure was recorded in an anesthetized canine preparation with an isolated, isovolumetric left heart. Intrasinus pressures were changed in steps of 50 mm Hg to produce either an increase or decrease in pressure from a mean level of 150 mm Hg. The response to eight combinations of increases and decreases in left- and right-sided pressures was examined. Blockade of the sympathetic impulses to the heart produced a loss of response of left ventricular systolic pressure when the intrasinus pressure was decreased from 150 to 100 mm Hg. Parasympathetic blockade produced a loss of response to an increase in pressure from 150 to 200 mm Hg. Left ventricular systolic pressure was more sensitive to a decrease in pressure from 150 to 100 mm Hg in the right sinus than in the left, but there was no difference in sensitivity between left and right sides when intrasinus pressure was raised from 150 to 200 mm Hg. The summation pattern of the response to simultaneous steps in left and right pressure was mutually facilitative for steps from 150 to 100 mm Hg and mutually inhibitory for steps from 150 to 200 mm Hg. The entire system was simulated with a hybrid computer model consisting of separate functional relations used to represent the baroreceptors, central nervous system, and left ventricle. Due to the baroreceptor characteristics and other nonlinearities, the simulation results suggest that a careful distinction should be drawn between transient and steady-state responses when assessing the relative role of each autonomic division in any baroreceptor reflex.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Fiber orientation across the left ventricular myocardial wall has been studied. Specimens were obtained from 18 dog hearts rapidly fixed in situ in systole, in diastole, and in dilated diastole. Fiber orientation was determined across the free wall at eight sites from a T-shaped specimen by measurements with light microscopy in serial paraffin sections. Results indicate: (1) The wall has a well-ordered distribution of fiber angles varying from about 60° (from the circumferential direction) at the inner surface to about –60° on the outer surface. The greatest change in angle with respect to wall thickness occurs at the two surfaces (endocardial and epicardial). (2) Fiber angles did not change significantly during the transition from diastole to systole, despite a 28% increase in wall thickness (except in the papillary muscle root region). (3) The proportion of fibers lying in the sector of fiber angles oriented circumferentially (0±22.5°) to those oriented longitudinally (67.5 to 90° and –67.5 to –90°) is approximately 10:1. This ratio increases toward the base and diminishes toward the apex of the left ventricle. (4) All fiber angles in the lateral wall of hearts in systole increased through the wall by approximately 7° near the base and 19° near the apex relative to their counterparts in diastole, indicating bending or torsion of the left ventricle during contraction.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Femoral arterial diameter and pressure were measured in anesthetized dogs. Immediately after section of the ipsilateral lumbar sympathetic chain the artery dilated, reaching a maximum of 122.0% (±0.56 SEM) of resting diameter within 30 to 40 seconds. Later the diameter diminished, stabilizing at 104.3% (±1.8 SEM) of resting diameter within 15 minutes. Stimulation of the peripheral stump of the sympathetic chain induced frequency-dependent constriction, the frequency-response curve being hyperbolic. The average maximal response was 13.42% (± 1.19 SEM) of the resting diameter. These changes were not dependent on suprarenal secretion, blood flow, or changes in distal vascular bed resistance. The contraction of the artery was slow. The half-time of stabilized contraction was 21.6 seconds at a stimulus frequency of 1/sec and 36.8 seconds at 25/sec. The half-time of relaxation was shorter (10.7 seconds and 21.5 seconds, respectively) and also frequency-dependent. A significant dilatation, after stimulation, inversely proportional to the stimulation frequency, occurred after low-frequency stimulations. The time course of contraction suggests the activation of individual smooth muscle layers successively more remote to the nerve endings, possibly due to diffusion of transmitter liberated at the nerve endings by stimulation.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Interactions between Purkinje fibers and ventricular muscle were studied in canine Purkinje-papillary muscle preparations. The change in duration of action potentials across the junctions between Purkinje fibers and papillary muscle was continuously graded, not abrupt. The transmembrane action potentials were longest in the false tendons and progressively shorter in more peripheral fibers. The responses of terminal Purkinje fibers and of neighboring muscle cells differed little in duration. The shortest action potentials were found in muscle fibers located in regions devoid of specialized tissue (tip of papillary muscle). These results suggest that the intercellular connections, including those at the junctions, offer relatively low resistance to current flow. During repolarization the current flowing between neighboring elements with intrinsically different repolarization times should therefore minimize the disparity in action potential durations on the two sides of the junctional site; a continuously graded change in duration would result. Because of this continuous gradation, premature ventricular responses initiated at the tip of the papillary muscle could be blocked, depending on the degree of prematurity, at various levels in muscle fibers functionally close to terminal Purkinje fibers or within the Purkinje system.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID