摘要:

The hydraulic load presented to the left ventricle by the systemic circulation was characterized by expressing pressure-flow relationships in the ascending aorta as input impedance. This was determined by spectral or Fourier analysis of simultaneously recorded pressure and flow waves in 1 unanesthetized and 27 anesthetized dogs. Impedance modulus fell steeply from its value at zero frequency (the peripheral resistance) and its value was lowest (less than 1/20th of the peripheral resistance) over that band of frequencies (usually between 1.5 and 10 cycle/sec) which contained most of the energy of the left ventricular ejection (flow) wave. The patterns of modulus and phase of ascending aortic impedance were found to result from the presence of two functionally discrete reflecting sites in the systemic circulation, one in the upper part of the body and the other in the lower. The presence of these two sites appears to be an important factor in maintaining a low impedance modulus between 1.5 and 10 cycle/sec, and so in providing a favorable impedance to pulsatile flow from the heart. Both modulus and phase of impedance in the ascending aorta showed changes similar to those seen in other arteries when blood pressure was altered and when vasodilation occurred in the vascular bed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

In 40 lightly anesthetized dogs, 5 to 30 days after surgical preparation, flow was measured simultaneously in the venae cavae, pulmonary artery, pulmonary vein, and aorta with ultrasonic flowmeters. Intrapleural and pericardial pressures were measured via silastic cannulas. Pulmonary vein diameter was monitored by miniature mutual inductance coils. In the resting animal with sinus arrhythmia, inspiration increased heart rate and flow in the vena cava, and to a lesser extent, in the pulmonary vein. Left ventricular stroke volume (LVSV) varied directly with the right ventricular stroke volume (RVSV) in dogs with slow heart rates. Cardiac tamponade invariably caused tachycardia and a marked decrease in cardiac output, arterial pressure, pulse pressure, and stroke volume; venous pressure and diameter increased. Pericardial pressure, although markedly elevated, fell with inspiration paralleling the fall in intrapleural pressure. Flow in the pulmonary vein rose or remained constant with inspiration. Pulmonary vein diameter frequently increased with inspiration during tamponade, but only after the pulmonary artery diameter increased with the inspiratory surge. LVSV did not decline sharply with inspiration, and actually increased within 2 beats of the increase in RVSV. The sum of LVSV plus RVSV increased markedly with inspiration, contradicting the concept of fixed intrapericardial volume. Almost all of the changes of pulsus paradoxus reflect the normal respiratory effects on the RVSV, delayed by transit through the pulmonary bed and exaggerated by the small LVSV in a vasoconstricted state.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Simplified methods are described for the measurement of human plasma renin “concentration” (PRC) and “activity” (PRA) based on the denaturation of renin substrate in which separation and concentration steps are avoided and recovery of renin is complete. In the PRA method effective inhibition of angiotensinase is achieved by warming plasma at pH 4.5 with EDTA followed by dialysis to pH 7.5. Neither renin nor renin substrate is affected by this treatment. In the PRC method, renin substrate is selectively denatured by warming at pH 3.3. After dialysis to pH 7.5 and addition of a standard substrate prepared from nephrectomized sheep, incubation results in a linear increase of pressor material which is assayed without extraction on rat blood pressure against synthetic angiotensin. Specificity is established by nephrectomy and immunological studies. The linear relationship between plasma renin concentration and reaction rate contrasted with the nonlinearity observed with renal renin. The systems are suitable for routine diagnostic use.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

It has been reported that previously administered dipyridamole intensifies the coronary vasodilator action of adenosine compounds. In the present study, a combination of dipyridamole and ATP at doses that alone are ineffective was examined for its effect on the coronary sinus blood flow. In 10 anesthetized dogs, heart rate, arterial blood pressure, cardiac output, and coronary sinus blood flow were measured before and during a 20-min constant-rate infusion of (a) ATP alone, 1 mg/min; (b) a combination of ATP, 1 mg/min, and dipyridamole, 0.005 mg/kg/min; and (c) dipyridamole alone, 0.005 mg/kg/ min. Coronary sinus flow was measured by a newly developed thermodilution flowmeter. Consistently during the infusion of ATP or dipyridamole alone no changes in the measured parameters occurred, whereas during infusion of the combination a very marked and sustained elevation (+493%) of coronary flow occurred, associated with a moderate increase in cardiac rate (+37%) and output (+42%) and a decrease in arterial blood pressure (−17%). In 7 other dogs, coronary vasodilator responses to ATP were determined before and 1 hour after a single 10-mg dose of dipyridamole. After dipyridamole, the coronary vasodilator action of ATP increased 5- to 100-fold. In a third group of 3 dogs, dipyridamole did not enhance the coronary vasodilator effects of nitroglycerin, bradykinin, or acetylcholine.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Thoracic aortic segments of 12 mammalian species were fixed while distended at normal physiological pressures after the vasa vasorum were filled by a perfusion mixture containing gelatin and carbon. Mammals whose aortas had 29 or fewer medial lamellar units had no demonstrable intramural vascular channels; those whose aortas had more than 29 medial lamellar units, had medial vasa. Aortas with medial vasa vasorum always had a subintimal medial zone devoid of vasa vasorum. In growing animals the width of this avascular zone increased with age; in adults, the width increased slightly with increasing species body weight. However, the number of lamellar units in the avascular zone was independent of both age and species and equal to 29.0 ± 2.5. All of the species with intramural aortic vasa vasorum as adults had 29 or more aortic medial lamellar units at birth; none of the species which had 29 or fewer lamellar units at birth had more than 29 lamellar units at maturity. In aortas with medial vasa vasorum, widening of the avascular zone during growth appeared to be due only to the uniform thickening of each of the approximately 29 lamellar units already present at birth; the vascularized outer zone widened both by enlargement of its lamellar units and the addition of new lamellar units. Species differences in medial distribution of vasa vasorum are due primarily to differences in thickness of the vascularized outer zone.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Two inbred substrains of Long-Evans rats have been maintained under identical laboratory conditions. In one substrain (Olson-Goss) 25% of the neonates have spontaneously occurring membranous ventricular septal defects; in the other (California) only 4% are affected. Since a genetic etiology was indicated, two series of reciprocal crosses were made to evaluate the possibilities that the defects might result from an abnormal fetal genotype, a genetically abnormal intrauterine environment, or both. In both series parents of a highly defective litter (“high-incidence” pairs) were reciprocally mated to parents of a completely normal litter (“low-incidence” pairs). In Series I, all parental pairs were Olson-Goss animals; in Series II, the low-incidence pairs were California animals. Substitution of a low- for a high-incidence male consistently and appreciably decreased the incidence of defects in the progeny of high-incidence females. Conversely, low-incidence females produced a relatively large number of defective pups when mated to high-incidence males. These data suggest that the primary factor responsible for septal malformation is the fetal genotype rather than the intrauterine environment. Patroclinous reciprocal cross differentials, particularly marked in the substrain crosses, suggest, however, that secondary factors may also be implicated.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The effects of quinidine and its interactions with potassium (K) on atrio-ventricular (A-V) conduction were studied in isolated, perfused rabbit hearts, utilizing microelectrode techniques. Quinidine gluconate (10 mg/liter) was added to perfusion fluid containing either normal [K+] (4.5 mEq/liter), low [K+] (1.5 mEq/liter), or high [K+] (7.5 mEq/liter). The following observations were made: (A) The marked prolongation of A-V conduction time produced by quinidine was antagonized by low K+and enhanced by high K+concentration. (B) Quinidine or high K+concentration prolonged the A-V interval by slowing intra-atrial and His-Purkinje-ventricular conduction. (C) Low K+concentration depressed conduction in the N region of the A-V node. (D) Lowering K+concentration in the presence of quinidine shortened the A-V interval by enhancing His-Purkinje-ventricular conduction. (E) Quinidine and high K+concentration increased the action potential amplitude in the nodal and the node-His regions of the A-V node while low K+concentration showed opposite effects. Hence, different regions of the A-V conducting system were selectively influenced by these agents. A-V conduction in the presence of low K+and quinidine depends upon the net results of their antagonism within individual fiber types. The importance of these interrelationships in pharmacologic approach to A-V conduction disturbances is stressed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Whether a change in myocardial contractility is accompanied by a change in diastolic extensibility was studied by altering stimulation frequency, including paired stimulation, as the inotropic intervention. Isometric and isotonic contractions of isolated cat papillary muscles were examined. Apparent changes in diastolic extensibility were observed with paired stimulation in isometric preparations. Rapid changes were seen only in muscles that had spontaneous aftercontractions between driven beats. These changes were believed not to reflect true extensibility changes but rather a change in timing between the relaxation of a beat driven by a paired stimulus and the onset of an aftercontraction. In continuous isotonic (not afterloaded) preparations, end-diastolic length depended on beat frequency. The muscle crept to a longer length when diastole was prolonged by decreasing the heart rate. In isotonic experiments without aftercontractions myocardial extensibility remained unchanged during paired electrical stimulation and changes in beat frequency.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID