Effect of body position on measurements of diffusion capacity after exercise.
BACKGROUND
Pulmonary diffusing capacity for carbon monoxide (D1co), alveolar capillary membrane diffusing capacity (Dm), and pulmonary capillary blood volume (Vc) are all significantly reduced after exercise.


OBJECTIVE
To investigate whether measurement position affects this impaired gas transfer.


METHODS
Before and one, two, and four hours after incremental cycle ergometer exercise to fatigue, single breath D1co, Dm, and Vc measurements were obtained in 10 healthy men in a randomly assigned supine and upright seated position.


RESULTS
After exercise, D1co, Dm, and Vc were significantly depressed compared with baseline in both positions. The supine position produced significantly higher values over time for D1co (5.22 (0.13) v. 4.66 (0.15) ml/min/mm Hg/l, p = 0.022) and Dm (6.78 (0.19) v. 6.03 (0.19) ml/min/mm Hg/l, p = 0.016), but there was no significant position effect for Vc. There was a similar pattern of change over time for D1co, Dm, and Vc in the two positions.


CONCLUSIONS
The change in D1co after exercise appears to be primarily due to a decrease in Vc. Although the mechanism for the reduction in Vc cannot be determined from these data, passive relocation of blood to the periphery as the result of gravity can be discounted, suggesting that active vasoconstriction of the pulmonary vasculature and/or peripheral vasodilatation is occurring after exercise.
Stewart
I B
IB
University of British Columbia, Allan McGavin Sports Medicine Center, Vancouver, Columbia, Canada. kiwi@interchange.ubc.ca
Potts
J E
JE
McKenzie
D C
DC
Coutts
K D
KD
D000328:Adult; D001810:Blood Volume; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D011653:Pulmonary Diffusing Capacity; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology