Effects of beta-adrenergic blockade on ventilation and gas exchange during the rest to work transition

The purpose of these experiments was to determine the effects of acute beta-blockade on the kinetics of oxygen uptake (V̇o₂), expired carbon dioxide (V̇oo₂), and expired ventilation (V̇E) in the transition from rest to submaximal exercise. Six male subjects exercised for 6 min on a cycle ergometer (60 W) initiated as a square wave form rest on two occasions. The beta-blockade experiment began 60 min after the subejct ingested propranolol hydrochloride (1 mg·kg^-1 BW) while the second experiment served as control with the treatment order counterbalanced. Ventilation and gas exchange were monitored by open circuit techniques and the data were modeled with a single-component exponential function using a time delay. No differences existed (p > 0.05) in the steady state V̇o₂, V̇co₂ and V̇E nor the kinetics of V̇E between treatments. However, the rate of adaptation of V̇o₂ toward steady state was significantly slowed (p < 0.05) with beta-blockade. These data suggest that acute beta blockade results in diminished V̇o₂ kinetics in the transition from rest to steady-state exercise. We hypothesize that the mechanism to explain this finding is a slowed time course of cardiac output adjustment at the beginning of exercise.