PULMONARY CAPILLARY BLOOD-VOLUME DURING LOWER-BODY NEGATIVE-PRESSURE - EFFECT OF GENDER

Background: The purpose of this study was to examine the changes in pu lmonary capillary blood volume (Vc) in men and women during lower body negative pressure (LBNP). Additionally, the components of lung diffus ion capacity were measured and evaluated for the effect of gender and LBNP. Methods: There were 6 men and 6 women who underwent a staged LBN P protocol to -40 mm Hg. The diffusion of the lung for carbon monoxide (DLCO) was determined at two levels of inspired oxygen (21% and 60%). DLCO was separated into the diffusion capacity of the membrane (DLM) and the diffusion capacity of blood. Results: During supine rest, DLCO values for men were larger than for women and were 39.8 +/- 3.8 and 3 2.2 +/- 2.2 ml.min(-1).mm(-1) Hg, respectfully. DLCO decreased equally with each stage of LBNP for men and women. Ve during supine rest was greater for men (131 +/- 8 mi) than for women (92.7 +/- 7 mi). Ve also declined with each stage of LBNP, and the decline was similar for men and women. DLM did not change with LBNP. Conclusion: The decrease in DLCO with LBNP is due to the reductions in thoracic blood volume in bo th men and women. These thoracic blood volume changes do not explain t he previously reported reduced tolerances to LBNP for women because th e reductions in thoracic blood volume were similar for men and women.