Pulmonary capillary blood volume and diffusing membrane capacity during exercise in humans: role of pulmonary artery pressure.

Abstract

During exercise, lung diffusing capacity for carbon monoxide (DL_CO), pulmonary capillary blood volume (V_c), and diffusing membrane capacity (D_M) increase secondary to a rise in pulmonary artery pressure (PAP) and central blood volume mobilization. While the role of central blood volume on DL_CO is well established, the impact of PAP on DL_CO, V_c, and D_M during exercise is less clear. Based on previous work, we tested the hypothesis that acute increases in PAP will potentiate exercise DL_CO via increases in D_M. Fifteen healthy young adults (7 females; age: 24±4 years) completed two bouts of cycling exercise at 60W, with (CUFF) or without (CON) bilateral thigh cuff inflation pressurized to 90 mmHg. The multiple fractions of inspired O₂-DL_CO method was used to determine DL_CO, V_c and D_M at baseline and during both exercise conditions alongside estimates of cardiac output (Q̇_c; impedance cardiography), and right ventricular systolic pressure (RVSP; echocardiography). CUFF exercise resulted in a larger increase in RVSP (CUFF: 44.7±6.1 vs. CON: 38.9±5.5 mmHg; P=0.036), but not Q̇_c (P=0.644) or V̇O₂ (P=0.976) compared to CON. DL_CO was higher during CUFF exercise (CUFF: 41±6 vs. CON: 38±6 ml/min/mmHg; P=0.001), and was mediated by increases in D_M (CUFF: 138±55 vs. CON: 90±39 ml/min/mmHg; P=0.032), not V_c (CUFF: 85±18 vs. CON: 98±27 ml/min/mmHg; P=0.820). Increases in RVSP were positively related with D_M (r_rm=0.82; P=0.024) but inversely related with V_c (r_rm=-0.80, P=0.029). Collectively, these data indicate that PAP primarily contributes to DL_CO during low intensity exercise via increases in capillary recruitment (i.e., D_M).