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While many studies have been carried out on the dynamics of the pulmonary circulation in experimental animals, few studies of this subject have been made in man until recently. With the advent of the cardiac catheter (1) it has become possible to make critical observations on the lesser circulation in health and disease.The volume of blood flowing through the pulmonary artery per unit of time is dependent upon the pressure in the pulmonary artery, the resistance to blood flow offered by the pulmonary vasculature, and the ability of the left side of the heart to handle the volume of blood which it receives. In this paper, the resting values for pulmonary blood flow, pulmonary arterial pressure, pulmonary "capillary" pressure, the pulmonary artery-pulmonary "capillary" pressure gradient, and the pulmonary arteriolar resistance are presented. In addition, the interrelationships of these various components of the pulmonary circulation as affected by increased blood flow through the lung, by elevated pressures in the pulmonary artery, and by high pressures in the pulmonary capillaries have been analyzed.

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Coronary blood flow and myocardial oxygen and carbohydrate metabolism were studied in normal intact dogs subjected to different degrees of hypoxia. Total left ventricular oxygen consumption was maintained during administration of 10 per cent and 5 per cent oxygen owing to increase in coronary flow and myocardial oxygen extraction. Ten per cent oxygen administration had little effect on carbohydrate uptake by the heart. Five per cent oxygen resulted in decreased coefficients of extraction for glucose, lactate and pyruvate, but total utilization was maintained. Complete anoxia resulted in negative arteriovenous differences for lactate and markedly decreased or negative values for pyruvate. T HE biochemical changes in the myocardium during hypoxia have been previously studied by use of tissue slices or the heart-Lung and other open chest preparations. The present studies employ a technic for catheterizing the coronary sinus that enables the measurement of myocardial metabolism in intact animals 1 during different degrees of hypoxia. METHODSDogs were premedicated with morphine (3 mg. per kilogram of body weight given subcutaneously) and anesthetized 30 minutes later by a 50/50 mixture of Nembutal and dial urethane* (0.025 cc. per kilogram). A systemic artery, pulmonary artery and the coronary sinus were catheterized by technics previously described, 2 and the coronary blood flow in terms of cubic centimeters per minute per 100 Gm. of left ventricle was measured, using the nitrous oxide desaturation technic. 1

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