Effects of atenolol, slow-release nifedipine, and their combination on respiratory gas exchange and exercise tolerance in stable effort angina.

The effects of atenolol, nifedipine, and their combination on gas exchange and exercise tolerance were studied in 27 patients with effort angina and normal global ventricular function in an open-label and randomized cross-over trial. Symptom-limited semi-supine exercise tests using a ramp protocol (20 W/min) with simultaneous breath-by-breath analysis of gas exchange were carried out after a 4-day wash-out period and after consecutive 2-week treatment periods with atenolol (50 mg b.i.d.), slow-release nifedipine (20 mg b.i.d.), and their combination (b.i.d.). Exercise tolerance was not significantly higher with atenolol than with nifedipine [118(24) vs 113(23) W]. Combination therapy [120(23) W] was more effective than monotherapy with nifedipine (p less than 0.05) but produced no further increase in exercise tolerance over atenolol monotherapy. Maximum oxygen uptake was not significantly different among the treatments. In the range of light to moderate exercise, the slope of the VO2-workload regression line expressed as ml.min-1.W-1 was lower with atenolol than with nifedipine [8.64(1.59) vs 10.28(1.74), p less than 0.005] and intermediate with combination therapy [9.99(1.83)]. The intercept on the VO2 axis was higher with atenolol than with nifedipine [366(111) vs 299(113) ml.min-1, p less than 0.05]. A similar pattern of results was seen when the drug effects on the slope of the VCO2-workload relation were analyzed. VE was higher with nifedipine than with atenolol at all points of the regression analysis [greater than 30 W].(ABSTRACT TRUNCATED AT 250 WORDS)