Pulmonary blood volume in rheumatic heart disease and its alteration by isoproterenol

Pulmonary blood volume was measured in five hemodynamically normal subjects and 37 patients with heart disease. Mean pulmonary blood volume in 25 of these patients with moderate to severe mitral stenosis, alone or complicated by other valvular lesions, was 359 ml. per M.2 (SE = +/-24 ml. per M.2), which was significantly higher than the average value of 230 ml. per M.2 (SE = +/-14 ml. per M.2) in the five normal subjects (p < 0.025). Multiple correlation of pulmonary blood volume with left atrial mean pressure, pulmonary vascular resistance, and stroke volume showed that each of these factors was significantly related to pulmonary blood volume, independently of the others. Increased left atrial pressure or stroke volume was associated with relatively high, and increased pulmonary vascular resistance with relatively low pulmonary blood volume. In seven subjects 10 to 20 mg. of isoproterenol administered sublingually led to a marked increase in pulmonary blood volume and a small decrease in pulmonary vascular resistance. The average increase in pulmonary blood volume was 78 ml. per M.2, or 35 per cent of the control value (SE = +/-15 ml. per M.2), while the average drop in pulmonary vascular resistance was 1.3 R.U.M.2 (SE = +/-0.5 R.U.M.2). Since the change in volume was too large to be accounted for by arteriolar dilatation alone, and there was a simultaneous decrease in pulmonary arterial and left atrial pressures, isoproterenol apparently increased the distensibility of a large but as yet unidentified segment of the pulmonary vascular bed.