Effects of oral propranolol and exercise protocol on indices of aerobic function in normal man

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Abstract
The exercise responses to 2 different progressive, upright cycle ergometer tests were studied in 9 healthy, young subjects either with no drug (ND) or following 48 h of oral propranolol (P) (40 mg q.i.d. [4 times/day]). The ergometer tests increased work rate by 30 W either every 30 s or every 4 min. Propranolol caused a significant (P < 0.05) reduction in peak O2 uptake (.ovrhdot.VO2) during both the 30-s and 4-min tests (30-s ND, 3949 .+-. 718 ml/min (.hivin.x .+-. SD); 30-s P, 3408 .+-. 778 ml/min; 4-min ND, 4058 .+-. 409 ml/min; 4-min P, 3725 .+-. 573 ml/min). There was no difference between 30-s ND and 4-min ND for peak .ovrhdot.VO2. The ventilatory anaerobic threshold was not significantly different between any test (30-s ND, 2337 .+-. 434 ml O2/min; 30-s P, 2174 .+-. 406 ml O2/min; 4-min ND, 2433 .+-. 685 ml O2/min; 4-min P, 2296 .+-. 604 ml O2/min). The .ovrhdot.VO2 at which blood lactate had increased by 0.5 mM above resting levels was significantly lower than the ventilatory anaerobic threshold for the 4-min ND (1917 .+-. 489) and the 4-min P (1978 .+-. 412) tests, but was not different for the 30-s ND and 30-s P tests. At exhaustion in the progressive tests, the blood PCO2 [CO2 tension] was higher (P < 0.05) in both 30-s tests than 4-min tests. Steady-state submaximal cardiac output was reduced (P < 0.05) by propranolol. This was primarily due to a decrease in heart rate as stroke volume was significantly greater with propranolol than with no drug (P < 0.05). The duration of time at each stage of work rate in progressive exercise did not significantly affect the peak .ovrhdot.VO2 or the .ovrhdot.VO2 at the ventilatory anaerobic threshold. Short duration stages were associated with lwoer blood lactates for a given submaximal .ovrhdot.VO2 and with higher blood PCO2 at exhaustion. Propranolol had no significant effect on ventilatory anaerobic threshold or .ovrhdot.VO2 at a 0.5 mM blood lactate increase; however, propanolol did significantly reduce the peak .ovrhdot.VO2. Evidently in submaximal exercise, the cardiorespiratory system can compensate for propranolol induced changes. Above the anaerobic threshold, these compensations are inadequate.