Circulation Research

HEYMANN, MICHAEL A.

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The changes in circulation with advancing gestation were investigated in 44 fetal lambs in utero; gestational ages ranged from about 60 days to 150 days. Spinal analgesia was administered to the ewe, polyvinyl catheters were inserted into fetal vessels, and umbilical blood flow was measured by the steady-state diffusion Fick method during antipyrine infusion. Cardiac output, distribution of cardiac output, and actual organ blood flows were calculated from injections of nuclide-labeled microspheres (50μ diam) into a forelimb and into an umbilical or hindlimb vein. Umbilical Po

OLSSON, R. A.

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The use of a sensitive double-beam spectrophotometer and modifications in enzymatic assay techniques permitted the measurement of adenine nucleosides in extracts of canine left ventricle. In hearts not subjected to left coronary occlusion, adenosine content averaged 0.32 ± 0.04 (SE) nmole/g, increasing to an average of 1.82 ± 0.21 (SE) nmole/g after 15 seconds of coronary occlusion. The myocardial content of inosine plus hypoxanthine was 1.07 ± 0.21 (SE) nmole/g without coronary occlusion, rising to 1.98 ± 0.24 (SE) nmole/g after 15 seconds of coronary occlusion. Unlike the myocardial content of adenosine and inosine, the myocardial content of hypoxanthine did not appear to change during coronary occlusion.

GONZALEZ, NORBERTO C.

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In-vitro experiments performed in cat papillary muscles and strips of rat right ventricle suggest that the changes in myocardial contractility that follow acid-base disturbances are not a function of extracellular pH. Simultaneous changes in Pco

DAMATO, ANTHONY N.

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The site of origin and the sequence of atrial activation were studied in 21 open-chested dogs anesthetized with sodium pentobarbital. Bipolar plunge electrodes were used to record atrial electrograms simultaneously with surface lead II and His bundle electrogram. In sinus rhythm the sinus node was activated first, followed sequentially by Bachmann's bundle, right atrial appendix, left atrial appendix, posterior left atrium, and the proximal portion of the coronary sinus. In 15 dogs left atrial beats and rhythms of various rate were recorded, including instances of left atrial exit block and of rapid left atrial rhythms. In such beats one of the left atrial electrodes was activated first and was followed by Bachmann's bundle, sinus node, proximal portion of the coronary sinus, and by right atrial appendix. Left atrial beats were observed occurring (1) spontaneously; (2) as a result of vagal stimulation; (3) after destruction of the sinus node; (4) during ventricular pacing. Left atrial pacing through the electrode recording initial activity reproduced the sequence and configuration of atrial electrogram similar to that seen in the ectopic left atrial beats. These results demonstrate that in dogs ectopic activity frequently originates in the left atrium.

TAYLOR, ROGER R.

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Isometric, afterloaded and isotonic contractions of cat right ventricular papillary muscle were studied in vitro at 30°C or 37°C. The length to which muscle contracted under a given total load varied directly with initial muscle length. The discrepancies between contracted muscle lengths depended upon load and the inotropic state of the muscle. In control contractions at 12/min, the maximum discrepancy occurred at a load of 0.5 g or 1 g and averaged 0.47 ± 0.04 (SD) mm while after acetylstrophanthidin (0.75 μg/ml) the maximum discrepancy occurred between 3- and 5-g load and averaged 0.62 ± 0.07 mm (

SHEPARD, CAROLYN E.

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The endogenous production of carbon monoxide and the flow of hemoglobin to and from plasma were measured in 11 anesthetized dogs after pumping blood through an extracorporeal circuit for short periods. Two different pumps were used. In all animals the increase in CO production was greater than could be explained by catabolism of hemoglobin lost from plasma, an average of 11.4 times greater with one pump and 2.49 times greater with the other pump. Evidence is presented that this discrepancy could not be explained by catabolism of heme other than that of hemoglobin, and we therefore concluded that rates of hemoglobin catabolism were much greater than indicated by plasma hemoglobin kinetics and that extravascular hemolysis is a major cause of erythrocyte destruction during mechanically induced hemolysis. Extravascular hemolysis apparently caused an average of 72.9% and 37.2% (with the two pumps) of the total quantity of erythrocytes destroyed during pumping and for 3 hours after pumping.

COLEBATCH, H. J.H.

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Histamine constricts airways and pulmonary blood vessels in isolated lungs, but is said to dilate pulmonary blood vessels in intact animals. The present experiments test the hypothesis that histamine only constricts pulmonary blood vessels, and that dilatation depends on epinephrine released by histamine from the adrenal glands. In cats anesthetized with pentobarbital, the difference in pressure between the pulmonary artery (PA) and left atrium (LA) was related to pulmonary blood flow measured by dye dilution before, and at intervals of 0.5 to 2 minutes after PA injection of histamine. In intact or vagotomized cats histamine increased PA-LA pressure difference and pulmonary blood flow, but calculated pulmonary vascular resistance (PVR) decreased significantly at 1 minute; control values were restored in 4 minutes. In adrenalectomized cats, histamine (10 to 40 μg) increased PA-LA pressure and PVR, but did not change pulmonary blood flow. After beta-receptor blockade with propranolol, histamine (10 to 20 μg) had the same effect as in adrenalectomized cats. After adrenalectomy or propranolol, the histamine-induced increase in PVR was prolonged. When histamine had increased PVR in adrenalectomized cats, epinephrine (5 μg iv) reduced PA-LA pressure and PVR. Histamine infusion (5 μg/kg/min iv) decreased PVR in intact cats, increased PVR in adrenalectomized cats, and when epinephrine (5 μ/kg/min) was also infused, decreased PVR in adrenalectomized cats. The results support the proposed hypothesis. Release of histamine locally in the lungs may encourage distribution of both blood and gas flows away from damaged and toward normal respiratory tissue.

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FUNG, Y. C.

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The purpose of this study was to describe quantitatively the geometric organization of the pulmonary alveolar capillary bed. Conventional representation of these vessels as a tight network of circular cylindrical tubes (tube-flow model) was contrasted with a suggested alternative of a continuous sheet bounded on two sides by endothelium held apart by connective tissue and cellular posts (sheet-flow model). A vascular space-tissue ratio, VSTR, is defined as the ratio of vascular lumen volume to the circumscribing tissue volume. The VSTR was obtained by planimetric measurements. Formulas were developed to relate VSTR to the geometric models. Cat lungs were perfused in situ with liquid silicone elastomer at 25 mm Hg, and the liquid elastomer was allowed to catalyze at 15 or 25 mm Hg static pressure while the airway pressure was maintained at 10 cm H

HOFFMAN, BRIAN F.

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Action potential durations and local refractory periods were mapped along the course of canine conducting tissue from bundle branches to the termination of false tendons in ventricular muscle. Standard microelectrode techniques were used. Areas of maximum action potential duration, which coincided with areas of maximum local refractory periods, were consistently found 2 to 3 mm proximal to the termination of conducting fibers in muscle. The refractory periods at the areas of maximum action potential duration were quantitatively identical in the multiple false tendons of a segment of the conducting system, providing a uniform functional limit for the propagation of premature impulses across the distal end of the conducting system of the segments studied. It was demonstrated that appropriately timed premature impulses could be confined within conducting tissue either proximal or distal to the area of maximum action potential duration. This occurred when the area of maximum duration was still refractory, after other areas of the conducting system had recovered excitability. In most preparations, maximum action potential durations and functional refractory periods across distal false tendons were longer in tissue from the right side than from the left side of the conducting system.