To examine the effect of cardiac output (CO) on the gravity-nondependent distribution of pulmonary blood flow, 2 X 10(6) 99mTc-labeled albumin microspheres (20 microns) were injected at end expiration into dogs (anesthetized, supine, and breathing room air spontaneously). Two animals were injected at their resting CO, two were injected during increased CO (arteriovenous fistulas induced), and two were injected at low CO (phlebotomy induced). The chest was opened and the lungs were removed, drained of blood, and dried while fully inflated. Single-photon emission-computed tomography was performed on the dry lungs to map the distribution of activity in transverse, coronal, and sagittal slices. The results confirmed the presence of a central-peripheral gravity-nondependent gradient and showed that increases in CO were associated with increases in absolute flow to both the central and peripheral regions of the lung with persistence of the central-peripheral gradient. These observations were further confirmed by direct imaging of midcoronal slices. Examination of the average flow in vertical and horizontal slices showed that, when zone 1 was not present, changes in CO affected all slices uniformly, such that when the CO doubled, the absolute flow in every slice in all three planes also doubled. We conclude that, with the exception of recruitment and derecruitment of vascular channels in the upper regions of the lung (zone 1), when CO changes, the blood flow everywhere in the lung changes uniformly and in proportion to the CO. This uniform increase in blood flow is consistent with the three-dimensional nature and resistive properties of the pulmonary vascular tree.
- Copyright © 1989 the American Physiological Society