[Estimation of lung volume and pulmonary blood volume from radioisotopic images]

Lung volume and pulmonary blood volume in man were estimated from the radioisotopic image using single photon emission computed tomography (SPECT). Six healthy volunteers were studied in a supine position with normal and altered lung volumes by applying continuous negative body-surface pressure (CNP) and by positive end-expiratory pressure (PEEP). 99mTc labeled human serum albumin was administered as an aerosol to image the lungs. The CNP caused the diaphragm to be lowered and it increased the mean lung tissue volume obtained by SPECT from 3.09 +/- 0.49 l for baseline to 3.67 +/- 0.62 l for 10 cmH2O (p less than 0.01), and to 4.20 +/- 0.67 l for 20 cmH2O (p less than 0.01 as compared with 10 cmH2O), respectively. The PEEP also increased the lung tissue volume to 3.68 +/- 0.68 l for 10 cmH2O as compared with the baseline (p less than 0.05), but there was no further increase in the volume after applying 15 cmH2O PEEP. The lung tissue volume obtained by SPECT showed a positive correlation with functional residual capacity measured by the He dilution method (r = 0.91, p less than 0.001). Pulmonary blood volume was estimated by taking the ratio of gamma-counts in the lung field to those in the intracardiac space (L/H ratio) after the equilibration of intravascular 99mTc-labeled red blood cells. The L/H ratio decreased after either the CNP or PEEP, suggesting a decrease in the blood volume per unit lung volume.(ABSTRACT TRUNCATED AT 250 WORDS)