Pulmonary capillary blood volume during lower body negative pressure: effect of gender.

BACKGROUND

The purpose of this study was to examine the changes in pulmonary capillary blood volume (VC) in men and women during lower body negative pressure (LBNP). Additionally, the components of lung diffusion capacity were measured and evaluated for the effect of gender and LBNP.

METHODS

There were 6 men and 6 women who underwent a staged LBNP 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 32.2 +/- 2.2 ml.min-1.mm-1 Hg, respectfully. DLCO decreased equally with each stage of LBNP for men and women. VC during supine rest was greater for men (131 +/- 8 ml) than for women (92.7 +/- 7 ml). VC 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 both men and women. These thoracic blood volume changes do not explain the previously reported reduced tolerances to LBNP for women because the reductions in thoracic blood volume were similar for men and women.