Journal of Applied Physiology, Vol 55, Issue 2 529-533, Copyright © 1983 by American Physiological Society
Exercise gas exchange in asthmatics after beta-adrenergic blockade
D. Y. Sue, L. R. Van Meter, J. E. Hansen and K. Wasserman
Pharmacologic beta-adrenergic blockade reduces maximal heart rate (HR)
during exercise but variable results have been reported for minute
ventilation (VE), CO2 output (VCO2), and O2 uptake (VO2). A total group of
19 subjects with mild asthma was studied. We studied 16 subjects from the
group who received placebo or pindolol, a beta-adrenergic antagonist,
during 1-min incremental exercise on a cycle ergometer. During incremental
exercise, HR, VE, VCO2, and VO2 were less after beta-blockade than after
placebo at the same work rate below the anaerobic threshold. Maximal HR,
VE, VO2, VCO2, and work rate were significantly less after beta-blockade.
In addition, we studied six subjects from the group, including three who
had also performed incremental exercise, during the steady state of
constant-work cycling exercise. We found no difference in VE, VCO2, or VO2
although HR was less after beta-blockade. We conclude that beta-adrenergic
blockade affects gas exchange by delaying the normal cardiovascular
response to exercise. Decreased VE during incremental exercise is due to
slowed delivery of CO2 load to the lungs rather than alterations in
substrate, lung function, or ventilatory control.
