Measurement of human pulmonary arterial volume in vivo

A method of measuring pulmonary arterial transit time (PATT), from the pulmonary valve to the precapillary vessels, using the gamma-emitting isotope technetium-99m and external counting probes, has been applied in patients coming to cardiac catheterization. The method was successfully applied in 36 of 39 patients. The dose of 99Tc for a single determination was 1 mc. Agreement between right and left lung transit times was good, average difference between the two lungs being less than 7% of mean PATT. Reproducibility between duplicate injections was 9.4 +/- 1.2% (SEM). Pulmonary arterial volume (PAV) was calculated as the product of PATT and flow. In 11 normal patients average PAV was 92 ml . m-2 and constituted 30% of total pulmonary blood volume (PBV). In ten patients with pulmonary hypertension secondary to lung disease average PAV was 129 ml . m-2, constituting 38% of PBV, while, in seven patients with left ventricular disease and a similar degree of pulmonary hypertension, PAV was also 129 ml . m-2, but constituted only 29% of PBV. Thus, in pulmonary hypertension secondary to lung disease the pulmonary arteries are enlarged out of proportion to the remainder of the pulmonary vascular bed. In seven patients with carcinoma of the lung, in whom one main branch of the pulmonary artery was occluded with a balloon catheter, PAV fell significantly less than would be predicted, indicating a distension of the unoccluded portion of the arterial tree. Distensibility in the unoccluded part of the arterial tree was calculated to be 4.5% per cmH2O pressure.