摘要:

A sheep preparation was developed for studying fetoplacental and neonatal blood volumes using isotope dilution techniques. Fetoplacental blood volume was measured in 46 fetal lambs (gestational age 112 to 146 days) using radioactive iodinated human serum albumin (125I-RISA). In 28 of the 46 animals, blood volume was also computed using125I-RISA and maternal red cells labeled with radiochromium (51Cr). Blood volume averaged 156.1 ml/kg of fetal weight with the single-label method and 134.7 ml/kg with the double-label method. Blood volumes measured in 17 neonatal lambs with the single-label technique averaged 110.0 ml/kg, and with the double-label technique in 10 animals averaged 104.0 ml/kg. Placental blood volume, determined by subtracting the neonatal blood volume from the fetoplacental blood volume, although varying from animal to animal, was independent of fetal weight and remained relatively constant during the last fourth of gestation.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The effects of stimulating the carotid sinus nerves on the distribution of cardiac output and peripheral vasoactivity was studied in intact, unanesthetized dogs instrumented with ultrasonic or electromagnetic flow probes on the ascending aorta, mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. A radiofrequency pacemaker was used to stimulate the nerves in dogs at rest, during treadmill exercise, and after autonomic blockade. Thirty-second periods of stimulation in the resting dog resulted in an average decrease in aortic pressure of 28%, cardiac output remained unchanged, total peripheral resistance fell 29%, mesenteric flow 12%, mesenteric vascular resistance 18%, renal flow 8%, and renal vascular resistance 22%. In the iliac bed flow increased by 90% while resistance declined by 62%. Heart rate decreased initially by 13%, and returned to control during stimulation. The bradycardia was determined to be predominantly due to vagal stimulation. During treadmill exercise carotid sinus nerve stimulation resulted in similar decreases in arterial pressure, mesenteric and renal resistance, and a further decrease in iliac resistance from exercise control values. Thus, electrical stimulation of the carotid sinus nerves in the conscious dog produced a differential pattern of peripheral vasodilatation, the most profound dilatation being observed in the hind-limb circulation. This release of sympathetic tone also occurred during stimulation in exercising animals when the muscular bed was already dilated on a metabolic basis.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The relationship between changes in perfusion pressure and ionic transfers in the vascular wall has been studied using the rat tail vascular bed perfused at constant flow rate. Perfusion pressure was increased by elevating venous pressure, or by infusing norepinephrine. The ensuing ionic shifts were monitored by means of Na+and K+electrodes. In both instances, the rise in pressure was associated with ionic redistribution measured as a gain in K+and a loss in Na+in the perfusing medium. The increase in pressure showed a close correlation with K+efflux from the vascular wall, and a somewhat more variable correlation with Na+influx. While the qualitative aspect of the ionic transfers was similar in the two conditions, their size differed. It was much larger during a rise in pressure induced by venous back pressure, in which condition the wall tension was also proportionately larger. The occurrence of ionic transfers in response to changes in transmural distending pressure was confirmed in the isolated artery, perfused in situ. It is suggested that vascular tension is directly related to step levels of transmembrane ionic distribution, and that this distribution is regulated by passive stretch.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Force-velocity-length (FVL) relations were obtained by determining the phase-plane tracings of velocity of shortening vs. length during isotonic contractions. These measurements were then replotted in a three-dimensional graph after correction for the series elastic extension during the isometric phase of the contractions as derived from a quick release contraction. On examining the influence of temperature (29° and 37°), preload, frequency of stimulation (12/min and 24−30/min), paired stimulation (PS), calcium (2.5 mM and 7.5 mM), and iso-proterenol (10-5M), it was shown that the surface created by the three-dimensional FVL relations of the contractile element (CE) is unique for a given state of contractility. Furthermore, the course of velocity vs. length is determined only by the instantaneous CE length, regardless of the contractile state of the CE, and is independent of the time after stimulation over a large portion of the shortening. From the intersection of the linear load-shortening relation observed for the CE with the load axis the maximum force (Po) development of the CE was derived. The highest values of this corrected Po(1.80 ± 0.13 kg/cm2) were seen following inotropic interventions such as PS, calcium, or isoproterenol. Using the corrected Po, truly hyperbolic force-velocity curves were constructed from which Vmaxand the Hill equation constantsaandbwere derived for the various inotropic interventions.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Pulmonary capillary blood flow was measured by the nitrous oxide-body plethysmograph technique in 21 patients with valvular heart disease or pulmonary thromboembolism during routine diagnostic cardiac catheterization. The studies were performed with a high-frequency phonocardiogram recorded from the pulmonary area to indicate the pulmonary valve opening at the beginning of right ventricular ejection. The pulmonary artery to capillary flow conduction time was measured from the time of pulmonary valve opening to the foot of the pulmonary capillary flow pulse. The conduction time was greater than 160 msec when the pulmonary artery pressure was normal. The fall in the conduction time in disease indicated elevated pulmonary arterial pulse wave velocity and this correlated well with the level of pulmonary arterial pressure (correlation coefficient 0.92,P< 0.001). This suggests that there is a reduced pulmonary arterial distensibility in the chronic pulmonary hypertension of valvular heart disease and thromboembolic disorders.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Recent morphologic studies of adult mammalian thoracic and abdominal aortic segments have shown that the adult human abdominal aorta deviates significantly from the usual pattern of medial lamellar architecture. In the present study medial growth of these two aortic segments from prenatal life to adulthood was compared in terms of medial architecture and calculated tangential tension levels. During prenatal life, these parameters were very similar in the two segments. However, the postnatal increase in the medial thickness of the thoracic segment was due mainly to the addition of lamellar units which increased in number from 35 to 56; only a minor contribution was made by increased thickness of each unit which changed from 0.012 to 0.017 mm. The converse was true for the abdominal segment; the number of lamellar units increased only from 25 to 28, but lamellar unit thickness increased strikingly from 0.012 to 0.026 mm. Calculated wall stress was similar in the two segments throughout growth, but tension per lamellar unit became disparate in the segments during the first decade of life, culminating in unusually elevated values in the adult human abdominal aortic media.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Right ventricular papillary muscles from hyperthyroid and normal cats were studied in vitro at 30°C, at contraction frequencies of 12, 30 and 60/min. At 12/min the contractility of hyperthyroid muscles was significantly greater than normal, as indicated by greater velocity of isotonic shortening, isometric tension development, and rate of tension development. Isotonically contracted muscle lengths were smaller and time to peak isometric tension less. At 60/min, velocity of shortening was still greater and time to peak tension less in hyperthyroid muscles, but isometric developed tension, rate of tension development, and isotonically contracted muscle lengths and shortening were not different. Increasing frequency from 12/min to 60/min resulted in immediate positive inotropic responses in both groups, but a smaller response in hyperthyroid than normal muscles. Over subsequent minutes, a slight decrease in contractility occurred in normal muscles but the decrease was significantly greater in hyperthyroid muscles. The difference in response to increasing frequency is attributed to more profound hypoxia in hyperthyroid muscles at high contraction frequencies. Predisposition of the muscle to hypoxia induced by hyperthyroidism then becomes an important determinant of the net effect of hyperthyroidism on myocardial contractility. The experimental situation is analogous to the coexistence, in vivo, of thyrotoxicosis and other conditions predisposing to coronary insufficiency, such as coronary artery disease or ventricular hypertrophy; that hyperthyroidism does not then augment contractile state in respect to tension development or muscle shortening helps explain the occurrence of thyrotoxic heart failure in response to the body's increased requirements for blood flow.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID