Journal of Applied Physiology, Vol 72, Issue 5 1764-1772, Copyright © 1992 by American Physiological Society
Kinetics of CO uptake and diffusing capacity in transition from rest to steady-state exercise
J. R. Kinker, A. S. Haffor, M. Stephan and T. L. Clanton
Division of Pulmonary and Critical Care Medicine, Ohio State University, Columbus 43210.
In the transition from rest to steady-state exercise, O2 uptake from the
lungs (VO2) depends on the product of pulmonary blood flow and pulmonary
arteriovenous O2 content difference. The kinetics of pulmonary blood flow
are believed to be somewhat faster than changes in pulmonary arteriovenous
O2 content difference. We hypothesized that during CO breathing, the
kinetics of CO uptake (VCO) and diffusing capacity for CO (DLCO) should be
faster than VO2 because changes in pulmonary arteriovenous CO content
difference should be relatively small. Six subjects went abruptly from rest
to constant exercise (inspired CO fraction = 0.0005) at 40, 60, and 80% of
their peak VO2, measured with an incremental test (VO2peak). At all
exercise levels, DLCO and VCO rose faster than VO2 (P less than 0.001), and
DLCO rose faster than VCO (P less than 0.001). For example, at 40% VO2peak,
the time constant (tau) for DLCO in phase 2 was 19 +/- 5 (SD), 24 +/- 5 s
for VCO, and 33 +/- 5 s for VO2. Both VCO and DLCO increased with exercise
intensity but to a lesser degree than VO2 at all exercise intensities (P
less than 0.001). In addition, no significant rise in DLCO was observed
between 60 and 80% VO2peak. We conclude that the kinetics of VCO and DLCO
are faster than VO2, suggesting that VCO and DLCO kinetics reflect, to a
greater extent, changes in pulmonary blood flow and thus recruitment of
alveolar-capillary surface area. However, other factors, such as the time
course of ventilation, may also be involved.(ABSTRACT TRUNCATED AT 250
WORDS)
