摘要:

Electrodes were chronically implanted in intact dogs at several locations on the atria and ventricles, and studies made of the effect of an elevated extracellular K+concentration on the spread of the sinus impulse throughout the atria. It was found that sinus activity propagates to the coronary sinus and ventricles at a time when the atrial muscle fibers have been rendered inexcitable. The finding of such a sino-ventricular rhythm supports the existence of a specialized conducting path between the sinus and the atrio-ventricular node; this path is particularly resistant to depolarization by potassium. Potassium-induced 2:1 sino-atrial block was described. In vitro experiments provided a demonstration that such block is frequency-dependent and due to marked prolongation of the refractory period provoked by high [K]0. It appears that the lengthened refractory period may be due to a marked reduction of the reactivation rate of the “sodium carrying system.”

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The presence of a periodic component in the atrial waveform of patients with chronic atrial fibrillation can be demonstrated by the use of autocorrelation techniques, and is interpreted as evidence for the presence of a periodic or almost periodic pacemaking mechanism. In twelve patients the average rate of this periodic element was 421 per minute with a range of 346 to 528. No correlation is present between increasing rate and disorder of the waveform.The presence of persistent random wavelets modifying the beat-to-beat spread of excitation generated by a periodic focal pacemaker is proposed as a unifying hypothesis explaining the variability of the atrial waveform in atrial fibrillation in man.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The glomerular volumes in the kidneys were studied in four species of mammals, including a desert rodent, the jerboa (Jaculus jaculus); the laboratory white rat (Rattus norvegicus); a semidesert-living subprimate, the “bush baby” (Galago senegalensis senegalensis); and a primate, the grivet monkey (Cercopitheus aethiops aethiops). The measurements of volume were made according to the method of Palkovits and Zolnai which gives quantitative statistical values for the relative volumes of the glomeruli. An exact relationship between the average of the glomerular volumes, kidney weight, and body weight was not found in these different mammals when compared to each other. If the average volumes of the cortical and of the juxtamedullary glomeruli are compared separately then it is seen that the desert-living animals have a much bigger difference in volume between the cortical and the juxtamedullary glomeruli than those animals which require free access to water. In the kidney of the desert rodent (jerboa) the difference in volume between the cortical and the juxtamedullary glomeruli is 101% and, in the semidesert-living “bush baby,” 169%. On the other hand the corresponding difference of volume in the laboratory white rat is only 21% and in the grivet monkey 28%. Considering the great functional importance of the juxtamedullary glomeruli and deep nephrons of the kidney in relation to dehydration, the large size of these structures can be regarded as an adaptation to life in an arid environment.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The present study was undertaken to evaluate the influence of heart failure on the cardiac stores of norepinephrine, and to elucidate the mechanisms responsible for the changes observed. Congestive heart failure was produced in the guinea pig by supravalvular aortic constriction. Significant reductions in both the concentration and content of norepinephrine in the ventricles were observed, the magnitude of changes being related to the severity of the constriction. The renal concentration of norepinephrine was not usually affected. Infusions of large quantities of norepinephrine produced elevations of ventricular norepinephrine concentrations which were significantly less in guinea pigs with heart failure than in normal animals. Injections of lesser quantities of radioactive norepinephrine also resulted in smaller amounts of this material in the hearts of animals with failure. Measurement of the decay of specific activity indicated that heart failure did not alter the net turnover of norepinephrine in the left ventricle. From these findings it has been concluded that a defect in the uptake and/or retention of norepinephrine exists in these hearts and that this defect may be responsible for the depletion of norepinephrine.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Dogs with thrombin-induced thrombi received I131rabbit antibody to dog fibrinogen and a day later were given antiserum to the rabbit gamma globulin. Scintillation scanning techniques successfully detected the site of thrombosis. Excision of the thrombi and surrounding blood vessels demonstrated deposition of radioactivity in the lesion. The immunologic removal of the gamma globulin from the circulating blood increased the difference between the radioactivity deposited in the lesion and that present in the blood. This accentuates the lesion and offers potential diagnostic advantage.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Atrial tachycardia and ventricular tachycardia were induced by electric stimuli applied to the heart in the modified dog heart-lung preparation. Cardiac oxygen consumption was measured by the direct Fick method. Left ventricular output was kept constant at about 900 ml/min and arterial pressure at 100 mm Hg during both atrial and ventricular pacing. An increase of heart rate from 130 to 157 beats per minute in atrial tachycardia, and from 130 to 158 beats per minute in ventricular tachycardia, increased cardiac oxygen uptake by 11.5% and 50% respectively (mean of seven experiments). The greater energy expenditure of the heart in ventricular tachycardia, when compared with atrial tachycardia at equivalent heart rates, was attributed to the asynchrony of fractionate contractions of the ventricular muscle when stimuli are applied to the ventricular surface. Total coronary flow increased in both types of tachycardia, but more in ventricular tachycardia.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Solutions of human cardiac myosin contain macromolecules which were visualized in the electron microscope by the shadow-casting technic. The dominant particle was observed to be rod-shaped, to have a globular expansion at one end, and to have a mean length of about 1500 Å. The molecule of human cardiac myosin was found to be morphologically similar to myosin molecules from canine cardiac muscle and rabbit skeletal muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The relationship between the pressure gradient and the instantaneous blood flow in the descending thoracic aorta was studied in six dogs. Instantaneous flow was calculated from the pressure gradient using the simple analog approach of Fry and the more elaborate calculations of Womersley. The flows computed by either of these techniques were essentially indistinguishable from one another and compared favorably with the “true” flow. The “true” flow at the point of pressure gradient measurement was determined indirectly from the flow signals of two electromagnetic flowmetering systems, one placed upstream and the other downstream from the point of pressure gradient measurement. The probes were placed sufficient distances from the site at which pressure gradients were measured so that the pulsations of the vessel at that site were unaffected by application and removal of the probes. Thus, the vessel was presumed to be in its normal pulsating state. It is concluded, first, that the simpler approach of Fry is the method of choice in large vessels such as the aorta because the results do not differ appreciably from those using the Womersley approach. Second, the favorable comparison of either of the pressure gradient techniques with the “true” flow is strong evidence for the validity of this method and places the theoretical considerations of Womersley and others on a firmer experimental footing than previously.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The effects of brief periods of cephalic hypoxia, hypercapnia, and ischemia upon the contractility of the normally oxygenated ventricular myocardium were studied in an innervated, isovolumetric, canine left ventricle preparation. The majority of responses to cephalic hypoxia were of two types in preparations with vagi and carotid sinus nerves still intact. (a) More frequently, peak left ventricular pressure changed in biphasic fashion, consisting of an initial depression of contractility followed by subsequent augmentation. (b) Less frequently, a monophasic enhancement of contractility appeared. After transection of either the vagi or the carotid sinus nerves, a monophasic facilitation of contractility was usually evoked by cephalic hypoxia. From these data, it was concluded that two opposing influences act simultaneously upon the ventricular myocardium during cephalic hypoxia in preparations with intact vagi and carotid sinus nerves. Central nervous system hypoxia enhances myocardial contractility; its effect is mediated principally via sympathetic pathways. Hypoxia at the level of the carotid chemoreceptors depresses contractility reflexly; the efferent limb of this reflex is mediated chiefly via the vagi. At any moment in time, the effect upon ventricular contractility is the result of these opposing influences.Cephalic hypercapnia produced effects similar to those of hypoxia. Cephalic ischemia always evoked a marked, positive inotropic effect upon the ventricles.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The ventral caudal artery from DCA hypertensive and control rats was excised, mounted in a plastic chamber, and perfused with Krebs-Henseleit solution. Diameter of the artery and flow through the artery were measured at perfusion pressures ranging from 0 to 150 mm Hg. During these perfusions, constriction of the arterial segment was produced by adding norepinephrine, vasopressin, angiotensin II or rat serum in concentrations known to produce submaximal contractions.Samples of each experimental artery before and after artificial perfusion were fixed, sectioned, and stained. The tunica media of hypertensive arteries was thickened. Also, degenerative changes were observed in the internal elastic lamina and adjacent tunica media. Structural thickening of the tunica media was due primarily to expansion of the extracellular space and also due possibly to muscle fibre hypertrophy.In the absence of contraction, flow through the hypertensive artery was moderately reduced at all pressures because its lumen was narrowed by the thickened wall.Total wall tension, muscle tension, and elastic tension of the artery were estimated from the pressure-flow-radius data. Strength of muscular contraction was then measured in terms of work performed during contraction at a constant pressure. From this analysis, the muscle fibres in hypertensive arteries were found to be unequivocally hyper-responsive to norepinephrine, vasopressin, and rat serum. The possible cause of this hyper-responsive property is discussed.Serum was collected both from normotensive and from hypertensive donor rats and its pressor activity tested on thein vitropreparation. The pressor activity in hypertensive serum was found to be significantly elevated.The elasticity of the hypertensive artery was increased in the absence of contraction and unchanged during contraction. No hypertensive artery was found to be stiffer than normotensive arteries. These changes are probably related to degeneration of elastin.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID