Factors altering pulmonary capillary perfusion

The fraction of pulmonary capillaries perfused (FPCP) was determined in dogs by the ratio of pulmonary extravascular water (PEVW) measured by simultaneous indicator dilution curves of I¹²⁵ radioiodinated serum albumin (RISA) and I¹³¹ iodoantipyrene to total weighed lung water. Cardiac output (CO) was varied by opening or closing chronic bilateral A-V fistulas. Lobar atelectasis was produced by obstructing the bronchus with an intrabronchial balloon. In control animals, the FPCP was 0.6 to 0.7 with a cardiac index (CI) of 3 to 4 L. per miunte per square meter. During hemorrhage, with a CI of 0.6 L. per minute per square meter, the FPCP was 0.54. During high blood flow (fistula open and CI, 5.2 L. per minute per square meter) the FPCP approached 1.0. Left lower lobar atelectasis (LLLA) had no effect on the FPCP, although the shunt fraction increased from 16 to 32 percent. These data indicate that pulmonary capillary recruitment is a linear function of CO between a cardiac index of 2 and 5 L. per minute. Over a short period, atelectasis does not change FPCP.