β-Blockade and oxygen delivery to muscle during exercise

Abstract

The most commonly observed effect of β-blockade on cardiovascular function has been a reduction in heart rate both at rest and during exercise. The body attempts to compensate by increasing stroke volume and (or) increasing the extraction of O2 from the blood to maintain O2 delivery to the muscle. This paper examines the roles of muscle mass involved in the exercise as well as the time course of change in cardiac output and peripheral blood flow in an attempt to understand whether O2 supply is limited by β-blockade. Experiments are reported in which the kinetics of cardiac output response at the onset of submaximal cycle exercise were slowed in subjects taking oral propranolol. Taken in consideration with other data from our laboratory and with data in the literature, it was concluded that β-blockade does impair O2 transport. The degree of impairment is dependent on the total muscle mass involved and the metabolic demand.Key words: blood flow, cardiac output, fatigue, propranolol, oxygen uptake.