ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY In small pieces of rabbit atrial myocardium, sustained periods of circus movement tachycardia were produced by the induction of a single properly timed premature impulse. By use of multiple intracellular and extracellular electrodes the spread of activation during the tachycardia could be analyzed accurately. Because in the present experiments there was no gross anatomical obstacle for the impulse to circulate around, we paid special attention to phenomena occurring in the center of the circus movement. We found that in the absence of an inexcitable central obstacle the center of a circus movement was invaded by multiple centripetal wavelets which converged in the very center of the circuit. On the basis of these observations we developed a new model of circulating excitation in cardiac tissue. The properties of this model (referred to as the “leading circle concept”) were compared with the behavior of circus movement around the anatomical obstacle. It turned out that both types of circus movement tachycardia responded differently to changes in basic electrophysiological properties such as conduction velocity and refractory period. For example, addition of carbamylcholine to the tissue bath caused a marked acceleration of the leading circle tachycardia, whereas circus movement in a ring of atrial tissue was hardly affected. On the other hand, depression of conduction velocity by exposure to moderate concentrations of tetrodotoxin had a more pronounced effect on circus movement in the ring preparations than on tachycardias based on a leading circle mechanism. Finally we suggest the use of the strength-interval curve —after some modification —to describe and predict the behavior of a leading circle tachycardia.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY The small arteries play an important functional role in establishing the increased peripheral resistance found in essential hypertension. This paper concerns the direct measurement of the intrinsic mechanical and contractile properites of two categories of small arterial resistance vessels in the mesenteric bed of 5-month-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The vessels had mean internal diameters of 246 μm and 153 μm when relaxed at 100 mm Hg effective transmural pressure. Segments (1 mm) were mounted in such a way that internal circumference could be controlled and the circumferential wall tension (T) measured. After mounting, each vessel was maximally activated (by K+depolarization at 37°C in the presence of 5 mM Ca2+) at an internal circumference for which AT was approximately maximal, where1T = Tactive- Trelaxed. From the average values of AT measured we have estimated (on the basis of Laplace's equation) that the SHR vessel would average values of1T measured we have estimated (on the basis of Laplace's equation) that the SHR vessels would have been able to contract against 34% greater pressures than the WKY vessels (P< 0.001). Optical measurements of the dimensions of these vessels showed a 23% greater wall thickness in the SHR vessels (P< 0.02). There were no significant differences in the calculated active wall stresses of the SHR and WKY vessels; this suggests that the greater contractility found in the SHR vessels may be due to their having a greater smooth muscle cell content. These vessel measurements have been examined as well as the rats' blood pressures and heart to body weight ratios. The comparison points to the possibility that the disturbance to the cardiovascular regulatory system which results in hypertension produces similar cellular responses in both the myocardium and the peripheral vasculature.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY The purpose of this study was to determine the time interval following coronary artery occlusion during which the administration of hyaluronidase exerts a significant protective effect on injured myocardium. Fortyeight open-chest dogs with coronary artery occlusion were studied. Fourteen were untreated (controls). Hyaluronidase (500 NF units/kg, iv) was administered 20 minutes (12 dogs), 3 hours (8 dogs), 6 hours (8 dogs), or 9 hours (6 dogs) after occlusion. Epicardial electrograms, recorded from 10 to 16 sites on the anterior surface of the left ventricle before, 15 minutes after, and 24 hours after coronary occlusion were analyzed for S-T segment elevation and changes in QRS morphology. Transmural specimens, excised 24 hours after occlusion from the sites at which the electrograms were recorded, were analyzed for creatine phosphokinase (CPK) activity and histological appearance. In all five groups, myocardial CPK depression, histological evidence of the extent of necrosis, and changes in QRS configuration correlated well with one another. In the controls, S-T segment elevation 15 minutes after occlusion (ST15m) correlated well with myocardial CPK depression, histological extent of necrosis, and changes in the QRS complex 24 hours later. When hyaluronidase was given 20 minutes, 3 hours, or 6 hours after coronary occlusion, myocardial salvage was reflected in significantly less myocardial CPK depression for any given ST15mless histological evidence of infarction, and less extensive changes in QRS configuration than in the untreated dogs, although there was a progressive reduction in tissue salvage as the time interval between occlusion and drug administration lengthened. Hyaluronidase administered 9 hours after occlusion had no demonstrable effect on the development of myocardial necrosis, suggesting that ischemic injury is totally irreversible by this time.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY The effect of stimulation of the nerves to the intestine on intestinal oxygen uptake and hemodynamics was examined in anesthetized cats. In the normally perfused gut, nerve stimulation results in a reduced vascular conductance followed by a partial escape from neurogenic vasoconstriction. The oxygen extraction ratio increases to an appropriate extent to maintain oxygen uptake at prestimulation levels during the escape plateau. In a gut perfused via a pump, a similar response was seen when pressure was held constant; however, when blood flow was held constant a constriction of precapillary sphincters was unmasked and there was a prolonged decrease in oxygen extraction ratios. The data are compatible with the hypothesis that nerve stimulation results in vasoconstriction of precapillary resistance vessels and precapillary sphincters in the gut. Oxygen consumption of the tissue declines dramatically but because of the reduced blood flow at the site of the sphincters there is a secondary dilation and an increased oxygen extraction as more capillaries are opened at any given time. The resistance vessels show escape during nerve stimulation in situations of constant pressure or flow, and the escape of blood flow due to escape of the resistance vessels is a separate phenomenon unrelated to the escape of the sphincters. The return of oxygen uptake to normal during the escape phase suggests that redistribution of intestinal flow does not occur during vascular escape from neurogenic vasoconstriction. An equation for quantification of the extent of vascular escape is presented.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY The mechanical properties of the normal left ventricular wall during diastole were studied in 15 chronically instrumented, conscious dogs. Left ventricular minor and major axis diameters and equatorial wall thickness were measured with implanted pulse-transit ultrasonic dimension transducers. Left ventricular and pleural pressures were measured with high fidelity micromanometers. Circumferential mural stress was calculated by using an ellipsoidal shell theory; circumferential strain was calculated by using a natural strain definition. The static elastic properties of the myocardium were estimated by fitting the stress-strain values at the points of diastasis during a vena caval occlusion to an exponential function. A modified creep test was used to evaluate the series viscous properties of the myocardium. Acute increases in systolic and diastolic loading were produced by inflating implanted aortic occluders for 15 minutes in five dogs. In these dogs, the static stress-strain curves were not altered significantly after this period of pressure loading, indicating tbat short-term series viscous properties are negligible. Parallel viscous properties were evaluated in 10 dogs by means of the variable rate stretch test of dynamic diastolic filling. A viscoelastic model incorporating a parallel viscous element fit the dynamic stress-strain data better and predicted the static elastic properties more accurately than a simple exponential model. Thus, the mechanical characteristics of the diastolic left ventricle can be represented most precisely by a viscoelastic model that includes a parallel viscous element.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY I assessed the role of the chemoreceptors (aortic bodies) supplied by the coronary arteries in the hypertensive response induced by left atrial injection of (200μg serotonin) in adult anesthetized dogs. I compared the pressor response induced by serotonin during normal coronary circulation with that during exclusion of the central coronary segments from which the coronary blood supply to the aortic bodies arises. Exclusion of the central segments reduced the pressor response significantly from the control responses. Exclusion of the coronary blood supply of the aortic bodies resulted in a reduction of the control response of more than 50% in only two of the 21 dogs. I conclude that although the aortic bodies supplied by the coronary arteries play a significant role in the total hypertensive response to injected serotonin, their role usually is not predominant.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY In two groups of dogs we studied the effect of right and/or left stellectomy on myocardial reactive hyperemia (RH) and on coronary blood flow distribution. In the first group of 14 conscious dogs, the percent repayment of flow debt produced by a 10-second occlusion of the left circumflex coronary artery was recorded with a Doppler ultrasonic flow probe and a hydraulic vascular occluder. The dogs were studied under control conditions, after right stellectomy and after left stellectomy and after administration of propranolol and phentolamine. Right stellectomy did not affect RH. RH was significantly increased by left stellectomy from 476 ± 71% to 622 ± 86% (+31%) at the spontaneous heart rate and from 407 ± 51% to 577 ± 106% (+42%) during pacing. Propranolol significantly reduced RH from 447 ± 25% to 390 ± 27% (-13%) at the spontaneous heart rate and from 456 ± 25% to 311 ± 24% (-32%) during pacing. Phentolamine significantly increased RH from 419 ± 63% to 517 ± 71% (+23%). Propranolol was effective after bilateral stellectomy, whereas phentolamine was not effective after left stellectomy. In the second group of 14 anesthetized dogs with constant heart rate (15 (im) microspheres were injected twice into the left atrium. The first injection provided a control measurement; in nine dogs the second injection was made after left stellectomy. Left stellectomy significntly increased the left ventricular endocardial to epicardial ratio from 1.7 ± 0.03 to 1.23 ± 0.04. We conclude that the sympathetic nervous system has a tonic influence on coronary circulation and that left stellectomy increases the ability of the coronary bed to dilate and improves the endocardial perfusion.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

SUMMARY Traditionally it is assumed that during cardiac depolarization the macroscopic current generators that produce electrocardiographic voltages can be represented as a uniform double-layer source, coincident with the macroscopic boundary between resting and depolarized cardiac fibers as measured with extracellular electrodes (“uniform” hypothesis). A segment of this boundary is thus considered as a current dipole oriented perpendicular to the boundary. We present evidence that, contrary to the above, the effective dipoles largely parallel the long axes of cardiac fibers (“axial” hypothesis). Calculated potentials in volume conductors differ markedly in the two cases. The magnitudes of rapid local “intrinsic” deflections also differ markedly. In our experiments, potential fields produced by stimulation at several cardiac sites and measured magnitudes of intrinsic deflections during normal depolarization and that caused by stimulation support the axial hypothesis and are incompatible with the uniform hypothesis. Our results suggest that axial orientation of sources is sufficiently strong so that predictions assuming the uniform hypothesis would be seriously in error, although the axial theory alone does not exactly describe all the measured potentials. Axial orientation of current generators must be considered in quantitative prediction of electrocardiographic potentials. Further study of the geometry of the intracellular depolarization boundary and its relation to fiber direction and to the frequency of lateral intercellular junctions is required to describe the generators exactly.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID