Effect of beta-adrenergic blockade on VO2 kinetics during pseudorandom binary sequence exercise

The effect of beta-adrenergic blockade on the dynamic response characteristics of oxygen uptake (VO2) was examined in seven healthy men. Cycle ergometer exercise consisted of a pseudorandom binary sequence (PRBS) with 15 units per sequence, each unit lasting 15 s, for a total period of 225 s. Work rate was either 25 W or 125 W. Six identical sequences were performed continuously in a single exercise test. Each subject was studied on three occasions after 48 h treatment of placebo (CON); a nonselective beta-blocker, propranolol (PROP); and a beta 1-selective blocker, metoprolol (MET). VO2 was measured breath-by-breath. The data were analyzed in the frequency domain by Fourier analysis to yield amplitude and phase shift coefficients for the relationship between the input work rate and output VO2. Time domain analysis was performed on the cross-correlational analysis of VO2 (output).work rate (input) to determine the total lag time. The amplitude of the VO2.W-1 relationship was lower (P less than 0.0022) and the phase shift was greater (P less than 0.0039) with beta-blockade compared to CON; no differences were found between PROP and MET. The total lag time was longer (P less than 0.0053) in PROP (34.3 +/- 2.2 s) and MET (34.4 +/- 1.6 s) compared to CON (29.8 +/- 1.3 s). These data indicate that beta-adrenergic blockade causes a significant slowing of kinetics of the O2 transport system as determined by both frequency and time domain analysis. In addition, the PRBS exercise test is a sensitive indicator of change in function of the O2 transport system.