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Twenty-three patients exhibiting coronary insufficiency on exercise have been studied at rest and at exercise prior to and following sublingual administration of nitroglycerin. The most consistent and marked effect of nitroglycerin was the reduction in pulmonary artery pressure, total pulmonary resistance, and right ventricular work at rest and during exercise. Our patients were grouped according to the degree of left ventricular failure as indicated by the abnormality of rise in pulmonary artery pressure during exercise. It became evident that nitroglycerin improved left ventricular function in terms of increased output and lessened pulmonary artery pressure in cases in which failure was most severe.

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Central blood volume (cardiac output times mean transit time) from right atrium to ascending aorta was determined by the indicator-dilution method in 22 open-chested dogs which had previously had their red blood cells tagged with Cr51. The actual amount of blood in the heart and lungs was calculated from the total radioactivity in the blended homogenate of these organs. The two measurements of central blood volume correlated well ( r = +.88), the indicator-dilution volumes averaging 12% greater. The discrepancy between measurements is probably related to the pulmonary circuit having a lower hematocrit than the large vessels. The results substantiate the use of the Stewart-Hamilton formula (cardiac output times mean transit time) to measure central blood volume.