Effect of changing lung mass on lung water and permeability-surface area in sheep

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Abstract
The effects of changing cardiac output and lung mass on pulmonary capillary surface area, lung water and hemodynamics were studied in 8 sheep. 51Cr-erythrocytes, 125I-albumin, 3H2O and [14C]urea were injected into the right atrium, and timed samples were collected from the aorta for the calculation of cardiac output (CO), extravascular lung water (EVLW) and permeability-surface area product (PS) for [14C]urea. CO was varied by opening and closing arteriovenous shunts and lung mass was decreased by first tying off the left lung followed by tying off the right lower lobe. Pulmonary arterial pressure (r = -0.741) and pulmonary vascular resistance (r = -0.700) increased as lung mass was decreased. CO decreased slightly (r = -0.470) while left atrial pressure was not changed (r = -0.144) by decreasing lung mass. There was a close correlation between EVLW and lung mass (r = 0.944) and between [14C]urea PS and lung mass (r = 0.672). [14C]urea behaves as a diffusion-limited tracer in a single pass through the lungs, since [14C]urea extraction decreased as flow per unit mass increased. The clinical use of multiple-tracer studies to measure EVLW and [14C]urea PS was supported.