摘要:

The mechanics of isometric contraction in the heart were studied in both isolated papillary muscle and in an innervated, isovolumetric heart in situ. The maximum rate of development of isometric tension (dp/dt) and the integrated isometric tension (IIT), were studied on a beat-to-beat basis. The results indicate: 1) At a given heart rate, both the IIT as well as dp/dt vary directionally as changes in end diastolic volume and fiber length. During isometric contraction, the ratio dp/dt/IIT is independent of changes in fiber length, and remains a constant for any given state of contractility. 2) At a constant heart rate, and at constant volume, cardiac sympathetic nerve stimulation markedly increases dp/dt and IIT. The ratio dp/dt/IIT is elevated to a new constant which is also independent of fiber length. 3) Increasing heart rate increases the ratio dp/dt/IIT. This increase is, however, small compared to the increase in this ratio produced by sympathetic stimulation at the same rate. 4) The effects of heart rate and sympathetic stimulation are additive. 5) Differences have been noted between the manner in which norepinephrine, calcium, and acetyl strophanthidin alter the mechanics of the isovolumetric ventricle. This evaluation of the myocardial contraction is also uninfluenced by the adequacy of ventricular relaxation. 6) Comparison of the isovolumetric ventricle with isolated papillary muscle yielded directly analogous results, indicating that the properties observed were intrinsic to cardiac muscle and are not dependent upon structural arrangements in the intact heart. It is suggested that this ratio dp/dt/IIT is a quantitative measure of the contractility of the myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

The effects of altering stroke volume, aortic pressure and heart rate on the duration of each phase of left ventricular systole were investigated in a denervated dog heart.Augmenting stroke volume was found to prolong ejection, shorten the isovolumic period and had little or no effect on the duration of total systole. Elevating mean aortic blood pressure shortened ejection time, prolonged the isovolumic phase and either had no effect or decreased slightly the duration of total systole. Increasing heart rate at constant aortic pressure and stroke volume reduced the duration of all phases of systole. Digitalis and norepinephrine shortened all phases of systole.These findings demonstrate that the duration of each phase of left ventricular systole is dependent upon existing hemodynamic conditions as well as on the contractile state of the myocardium. By means of intrinsic mechanisms the ventricle exhibits the remarkable capability of being able to adjust the duration of each phase of systole in a manner appropriate to changing hemodynamic conditions.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

As was the case with guinea pig atria, ouabain induced a small but significant increment in Ca45uptake and a drop of tissue Ca content in rat atria during the positive inotropic effect. In ouabain contractures, the uptake rate increased 87% to 170% and there was little increase in tissue Ca. Concentrations of the glycosides required to produce a positive inotropic effect and contracture in rat atria were 100- to 200-fold greater than those required in guinea pig atria.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

The propagation of the pulse wave through the canine pulmonary arterial tree has been evaluated by means of harmonic analysis. The apparent phase velocity varied both with frequency and distance as one would expect in the presence of reflected waves. The phase velocity was about 230 cm/sec for the inflated and 325 cm/sec for the deflated lung. Theoretical considerations as well as experimental results indicate that the major branches represent the primary reflection site for the pulse wave. The pulse pressure is transmitted across the pulmonary capillary bed, although at a high attenuation, and the transmission varies markedly with lung volume.The dimensions of the pulmonary arterial tree were evaluated from casts. Data for the length and cross sections of the various branches are given. The volume of the arterial tree as represented by the casts was 24 ml. The cross section of the various branches represents an ellipse rather than a circle, and the cross section ratios of the major branch points is considerably less than those postulated for optimal energy transfer. The implications of the geometrical findings for the relation between pressure gradient and flow are briefly discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

Purified diets containing cholesterol and deficient or adequate in magnesium were fed to young growing Cebus (fatuella) monkeys.Diet-induced magnesium deficiency resulted in weight loss, hyperirritability, and in several monkeys, convulsions.In addition to the expected hypomagnesemia, deficient animals also had decreased serum potassium levels. However, after several weeks on diet, the electrocardiogram of deficient animals showed significant changes consisting primarily of S-T segment depression and peaking of the T wave; changes usually seen in hyperkalemic states.Prior to sacrificing the animals, the tolerance to K-strophanthidin, a cardiac glycoside, was ascertained in both deficient and control animals. The cardiac glycoside was administered slowly by the intravenous route to anesthetized monkeys and the appearance of four consecutive ventricular premature contractions in the electrocardiogram was taken as the end-point. Deficient animals required approximately one-half the dose administered to control monkeys to develop extrasystoles.The histopathology consisted of marked vascular sudanophilic deposits and dense fibrous connective tissue plaques in the ascending and descending aorta of deficient monkeys. Control animals showed little, if any, vascular sudanophilia.The serum cholesterol concentration increased significantly in the deficient group while the rise seen in control monkeys lacked statistical significance.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

A photocell was used to record vibrations in a solution of white Hector bentonite passing through a constriction introduced into Tygon or cellophane tubing, or into a transparent flat flow section with distensible sides. These vibrations were compared with those simultaneously recorded from the walls of the model. Both vibration spectra were also subjected to frequency analysis. At low steady flow rates in either three-dimensional system, the jet lost its laminar characteristics downstream from the constriction, but this disturbance was not accompanied by wall vibrations. At somewhat higher flow rates, the eddies impinged upon the walls and set up local wall vibrations, below the audible range. At still higher velocities, the turbulence became greater and the wall vibrations spread along the walls and became audible. However, the frequencies of the fluid motion did not necessarily appear in the frequency spectrum of the walls. The amount of energy necessary to set the walls in motion was partly determined by their physical characteristics; vibrations were more easily produced in the thin, flexible cellophane than in the thicker Tygon. Thus, the absence of murmurs does not mean that flow is laminar nor does the presence of wall vibrations mean that they are audible.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

Male and female breeder rats spontaneously develop arteriosclerosis. This occurs first in the aorta and coronary arteries and subsequently in the carotid and intracranial arteries. The carotid arteries show mesenchymal cell proliferation in the media followed by subintimal swelling and mucoid deposition, elastosis, cartilaginous metaplasia and eventual bone formation. Lipid deposition occurs infrequently, and then only in advanced lesions in the media. Severe lesions are much more frequent in the female breeder and the tendency towards cartilaginous metaplasia and bone formation is peculiar to the carotid arteries. The cerebral arteries show little arteriosclerotic involvement except for aneurysm-like outpouchings of the internal elastic membrane associated with mucopolysaccha-ride accumulation about the sites of elastic tissue disruption. Despite severe fulminating arteriosclerosis in the carotid arteries, the cerebral arteries and the brain tissue itself show little or no significant evidence of degenerative change. These results are interpreted to mean that the cerebral arteries of the breeder rat follow a different physiological and morphological pattern of response than the rest of the arterial system.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

Cardiac output in the dog was measured by indocyanine green dilution in 24 hemorrhagic shock experiments. Total peripheral resistance (TPR) was calculated from the cardiac output and systemic arterial blood pressure. Early in the hypotensive phase resulting from hemorrhage to 50 mm Hg blood pressure, the cardiac output was 19.3±6.6 (SD) % of control and the total peripheral resistance was 199 ±73 (SD) % of control. During the hypotensive phase the peripheral resistance declined significantly. This decline in TPR was associated with a significant decrease in respiration and heart rates, indicating a partial failure of the neurogenic control of the cardiovascular system. Following transfusions of the shed blood, the TPR decreased to the control value, but during subsequent progressive decline in blood pressure, vascular resistance again increased. Occasionally, TPR again fell terminally as the blood pressure decreased below 60 mm Hg. Although there is evidence for partial failure of peripheral resistance vessel tone during severe hypotension and some evidence for this following reinfusion of the shed blood, this failure, when observed, is a minor component of the progressive cardiovascular failure and is not the cause of irreversibility.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

摘要:

Parallel-fibered strips of cardiac (cat papillary) and skeletal (frog sartorius) muscles were mounted in air and action potentials were externally recorded from the middle of the strip. Electric fields, oriented longitudinally with respect to the long axis of the cells, were applied. A pair of stimulating electrodes was located at each end of the strip to test for propagation. Under conditions of blocked propagation produced by addition of isotonic sucrose solution, the cells near the middle of the strip could be tested for direct response to longitudinal fields. In long-celled skeletal muscle, the sucrose solution produced simultaneously failure of electrical and mechanical response to stimulation across the strip as well as failure of propagation; stimulation at ten times threshold failed to elicit responses. However, in short-celled cardiac muscle, the sucrose solution produced failure of propagation first; electrical and mechanical responses to longitudinal field stimulation continued without a change in threshold. From these experiments it may be concluded that transverse membranes of high resistance are present in cardiac muscle; thus, radial currents are forced to flow through each cell membrane leading to direct excitation.

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1963

数据来源: OVID