Ramp work tests with three different beta-blockers in normal human subjects

Summary The effects of-blockade on the responses of oxygen uptake (), heart rate (HR) and blood lactate (La^–) were examined during ramp cycle ergometer tests (50 W·min^–1 ramp slope) in 8 healthy male volunteers. Each subject took placebo, or one of four different doses of three different-blockers (propranolol, metoprolol or oxprenolol) 2 h prior to each test for a total of 15 exercise tests. () was measured breath-by-breath, HR was sampled once per breath, and La^– was obtained every minute. Linear regression analysis was applied to and HR data to obtain the kinetic parameter total lag time (TLT) and a slope value. La^– was analyzed by a continuous exponential model with the lactate slope index (LSI) being derived from the individual response curves. Submaximal exercise HR was significantly depressed at the baseline as well as during the ramp tests by-blockade. TLT for HR was significantly affected by-blockade, with a dose dependent shift from a placebo value of 16 to 26 s with placebo to a value of -40 to -60 s at the highest dose. Slope of HR was significantly depressed relative to placebo. kinetics assessed by TLT were not significantly affected by-blockade. This slope of the vs work rate relationship was significantly less than placebo only at the highest dose of-blocker. The LSI was not significantly affected by-blockade. In contrast with the clear impairment of HR response to exercise during-blockade, both the and La^– responses appear to be relatively unaffected by-blockade during ramp exercise tests. However, the significant change in slope of the vs work rate relationship at the highest dose level indicates that the oxygen transport system is in fact impaired by-blockade. It is concluded that the ramp exercise test is not a sensitive means of detecting changes in oxygen transport kinetics during exercise with-blockade. Further, there were no differences between the three-blocking drugs.Supported by the Heart and Stroke Foundation of Ontario, and the Natural Sciences and Engineering Research Council of Canada