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

Endurance-trained athletes exhibit greater diffusing capacity for carbon monoxide (DLCO) at rest and during exercise as compared to 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 to untrained and that the supine position would elicit a greater DLCO response as compared to the upright position during exercise in both groups. Fourteen endurance-trained (Trained) individuals (O: 61.1 ± 4.4 ml∙kg∙min) and 14 Untrained individuals (O: 37.4 ± 3.0 ml∙kg∙min) 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 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) was increased with supine exercise (p=0.03). There was an apparent plateau in DLCO and V 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 to upright position in Trained individuals near-maximal exercise, suggesting a plateau may be reached at maximal exercise.