摘要:

Using dogs on heart-lung bypass and perfused hind-limb preparations, the effect of the relatively low molecular weight cardioactive plasma fraction on the peripheral circulation of dogs was investigated. This cardioactive plasma fraction raised the arterial blood pressure of dogs on bypass and increased the perfusion pressure in hind-limb preparations. The raised arterial pressure was found to be associated with increased blood flow through the coronary and splanchnic beds; flow through the hind limb decreased. Adrenalectomyand nephrectomy did not abolish these peripheral effects of this plasma fraction. It is concluded that the raised systemic arterial pressures recorded from intact animals following the injection of this plasma fraction may result, in part, from the effect on the peripheral circulation.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

The defibrillation threshold for various wave forms of condenser discharge, using capacitors from 4 to 200 μF, has been measured. Condenser discharge alone was used, or condenser discharge 0.25 henry (20 ohms) with an iron core series inductance, or condenser discharge, 0.29 henry (27 ohms) inductance, but without the iron core. Statistical analysis of the results showed that the last of these three circuits gave the lowest threshold voltage values. Optimal parameters of inductance-altered discharges are obtained with values of 24, 32, and 50 μF.Detailed analysis of the separate physical parameters of the discharge show that optimal pulse duration is 8.5 to 16.6 msec. Further increase of duration does not decrease the voltage or current for threshold shocks, but merely increases the energy delivered. Pulse duration appears to be one of the more important parameters for successful defibrillation, and for this reason, a series inductance is also important.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

The degree of temporal dispersion of recovery of excitability of premature ventricular responses, estimated as the range of local refractory periods at various points on the surface of the right ventricle, is greater within a radius of 10 to 15 mm from the stimulated site than at greater distances. The fibrillation threshold of early premature beats is significantly lower than that of responses initiated in fully excitable tissue. The effect of prematurity on the fibrillation threshold is greater at points near the site of origin of the premature response. The observed spatial and temporal relationships suggest that the fibrillation threshold is related inversely to the degree of asymmetry in the excitable field.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

Reproducible pressure-volume curves have been obtained from fresh left ventricles removed from 10 cats and 27 dogs. Electron microscopic observations of sarcomere length and structure in the walls of these chambers have been correlated with the parameters of passive filling. In both the dog and the cat a similar relation of sarcomere length to filling pressure is observed, a filling pressure of 12 mm Hg corresponding to a sarcomere length of 2.2 μ. Sarcomeres shorter than 1.85 μ are not observed under conditions of passive filling. Sarcomeres tend to be longest in the inner layer of the ventricular wall. Filling pressure is observed to be a more general and reproducible index of sarcomere length than absolute or normalized filling volume. H zones are often present in the sarcomeres of the ventricular wall with filling pressures greater than 15 mm Hg and sarcomeres greater than 2.3 μ in length. These findings are discussed in relation to previous studies of papillary muscle and in relation to mathematical models for the left ventricle. The present results indicate that the normal left ventricle functions along the ascending portion of the length-tension curve, where the end diastolic sarcomere lengths are 2.2 μ or less.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

Rhythmic fluctuations in heart rate and ventricular contractility at the frequency of the respiratory movements were observed in innervated, isovolumetric, canine, left ventricle preparations. The heart rate and contractility waves probably represent the radiation of activity from the respiratory centers to the cardiac autonomic centers within the central nervous system. In spontaneously beating hearts, the respiratory cardiac arrhythmia is mediated via the vagi predominantly, although a slight arrhythmia is still evident after bilateral vagotomy. The greater the vagal tone, the greater is the amplitude of the arrhythmia.In paced hearts, the contractility waves exhibit significantly greater phase lags than do the heart rate waves in unpaced beats. The magnitude of the contractility waves varies inversely with the respiratory frequency. These waves are more prominent after bilateral vagotomy. Therefore, sympathetic influences appear to predominate in the mediation of the contractility waves, although the change in wave amplitude after vagotomy must be ascribed partly to the deceleration of respiratory frequency which occurs after vagotomy. The contractility waves represent rhythmic augmentations of contractility above a base line level after vagal section.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

The mean oxygen consumption of relaxed isolated vascular smooth muscle segments was found to equal 0.61±0.94 SEM μliter/mg wet wt/hr in a medium of buffered Ringer-glucose, and 0.65±0.05 SEM uliter/mg wet wt/hr in a solution of dog plasma. The resting muscle RQ was found to equal 0.99±0.01 SEM in buffered Ringer-glucose solution. When stimulated by addition of epinephrine the muscle segment contracted on the average by 9% of its initial diameter with a corresponding increase of its oxygen consumption by an average of 30% over its relaxed value. It was noticed that with increased initial circumferential stretch of the muscle segment, the amplitude of contraction was much greater when a given amount of catecholamine was added. This increase of sensitivity to catecholamine produced by initial stretch, was accompanied by a parallel increase of oxygen consumption by the contracted muscle. A qualitative correlation between an estimated degree of contraction of arterial muscle and its oxygen consumption was demonstrated. More quantitative correlation will have to depend upon better methods of measuring both the tension developed and the degree of initial stretch.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

To evaluate more precisely the possible protective effect of hyperbaric oxygenation in experimental myocardial infarction, gradual occlusion of a coronary artery was produced in the pig. Ameroid constrictors designed to produce complete occlusion within 48 hours were placed on the left anterior descending coronary artery of 24 young farm pigs. Of these, 12 were placed in a hyperbaric chamber at 1.25 atmospheres absolute and allowed to breathe 100% oxygen for a maximum of 32 hours. For control studies 12 other pigs were handled in a similar manner outside the chamber while breathing air at normal atmospheric pressure. Pigs treated with hyperbaric oxygenation outlived the untreated pigs. Pathological and histochemical studies of the hearts revealed that pigs treated with hyperbaric oxygenation had a high incidence of myocardial infarction, whereas only two pigs in the untreated group showed any evidence of myocardial damage. These findings suggest that moderate but prolonged hyperbaric oxygenation may lengthen life during and after coronary occlusion. This prolongation of life may permit the development of pathologically detectable myocardial infarctions.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

In patients with combined aortic and mitral valvular insufficiency, the combined regurgitant fraction across both valves has been shown to equal the product of the regurgitant fractions at each valve. This relationship was validated in nine patients, and in eight other patients was used to predict the degree of regurgitation at one valve when the regurgitant fraction at the other valve and the combined regurgitant fraction were known. Confirmation of the predicted degrees of insufficiency were afforded by cineangiocardiography and surgical inspection. Information of considerable usefulness predicting the least possible degrees of valvular insufficiency could be obtained from the measurement of the combined regurgitant fraction alone.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID

摘要:

In innervated, isovolumetric left ventricle preparations, sudden elevations of pressure in the isolated carotid sinus elicited a 9.5% depression of left ventricular systolic pressure (LVSP). After blockade of sympathetic neuroeffector junctions by bretylium tosylate, equivalent intrasinusal pressure changes evoked a 6.8% reduction of LVSP. This response could be completely abolished by atropine sulfate or by cooling the cervical vagi. Therefore, under the conditions of the present experiments, the vagus nerves mediated a significant fraction of the reflex depression of ventricular performance induced by carotid sinus baroreceptor stimulation. An appreciable elevation of LVSP was produced by atropine and by vagal cooling after blockade of sympathetic junctions. This enhancement of ventricular performance is an indication of a tonic negative inotropic influence of the vagus nerves upon the ventricular myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1966

数据来源: OVID