Are there sex differences in the capillary blood volume and diffusing capacity response to exercise?

Abstract

Previous work suggests that women may exhibit a greater respiratory limitation in exercise compared with height-matched men. Diffusion capacity (Dl_CO) increases with incremental exercise, and the smaller lungs of women may limit membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc) in response to the increased oxygen demand. We hypothesized that women would have lower Dl_CO, Dl_CO relative to cardiac output (Dl_CO/Q̇), Dm, Vc, and pulmonary transit time, secondary to lower Vc at peak exercise. Sixteen women (112 ± 12% predicted relative V̇o_2peak) and sixteen men (118 ± 22% predicted relative V̇o_2peak) were matched for height and weight. Hemoglobin-corrected diffusing capacity (Dl_CO), Vc, and Dm were determined via the multiple-[Formula: see text] Dl_CO technique at rest and during incremental exercise up to 90% of V̇o_2peak Both groups increased Dl_CO, Vc, and Dm with exercise intensity, but women had 20% lower Dl_CO (P < 0.001), 18% lower Vc (P = 0.002), and 22% lower Dm (P < 0.001) compared with men across all workloads, and neither group exhibited a plateau in Vc. When expressed relative to alveolar volume (Va), the between-sex difference was eliminated. The drop in Dl_CO/Q̇ was proportionally less in women than men, and mean pulmonary transit time did not drop below 0.3 s in either group. Women demonstrate consistently lower Dl_CO, Vc, and Dm compared with height-matched men during exercise; however, these differences disappear with correction for lung size. These results suggest that after differences in lung volume are accounted for there is no intrinsic sex difference in the Dl_CO, Vc, or Dm response to exercise.NEW & NOTEWORTHY Women demonstrate lower diffusing capacity-to-cardiac output ratio (Dl_CO/Q̇), pulmonary capillary blood volume (Vc), and membrane diffusing capacity (Dm) compared with height-matched men during exercise. However, these differences disappear after correction for lung size. The drop in Dl_CO/Q̇ was proportionally less in women, and pulmonary transit time did not drop below 0.3 s in either group. After differences in lung volume are accounted for, there is no intrinsic sex difference in Dl_CO, Vc, or Dm response to exercise.

Keywords: diffusion capacity; exercise; pulmonary transit time; sex differences.