Impact of body posture on pulmonary diffusing capacity at rest and during exercise in endurance-trained and untrained individuals

Endurance-trained athletes exhibit a greater diffusing capacity for carbon monoxide (DLCO) at rest and during exercise as compared with untrained individuals; however, the mechanism(s) are unclear. The supine position translocates blood centrally and can be used to investigate DLCO responses independent of metabolic rate. We hypothesized that endurance-trained individuals would have a greater DLCO response to postural change at rest as compared with untrained and that the supine position would elicit a greater DLCO response as compared with the upright position during exercise in both groups. Fourteen endurance-trained (Trained) individuals (V̇o_2peak: 61.1 ± 4.4 mL·kg^-1·min^-1) and 14 untrained individuals (V̇o_2peak: 37.4 ± 3.0 mL·kg^-1·min^-1) completed DLCO maneuvers at rest and during exercise in the upright and supine position. At rest, there was a significant group-by-position interaction (P = 0.02) effect on DLCO with post hoc analysis determining DLCO increased from upright to supine position in Trained (P < 0.01), but not untrained (P = 0.58). There was no effect of position on exercising DLCO (P = 0.16) regardless of group; however, pulmonary capillary blood volume (V_C) was increased with supine exercise (P = 0.03). There was an apparent plateau in DLCO and V_C in the Trained group near-maximal exercise as Trained failed to increase DLCO (P = 0.25) and Vc (P = 0.46) up to near-maximal exercise. Trained individuals demonstrate greater DLCO recruitment with postural change at rest suggesting a greater ability to recruit/distend the pulmonary microvasculature. However, the supine position did not augment DLCO as compared with upright position in Trained individuals near-maximal exercise, suggesting a plateau may be reached at maximal exercise.NEW & NOTEWORTHY We demonstrate that the supine position increases resting DLCO significantly more in endurance-trained individuals as compared with untrained individuals. Furthermore, the supine position increases pulmonary capillary blood volume, but not diffusing capacity during exercise. Lastly, there was an apparent plateau in DLCO and V_C in the Trained group suggesting the pulmonary microvasculature may reach a morphological limit.