Ramp work tests with three different beta-blockers in normal human subjects.
The effects of beta-blockade on the responses of oxygen uptake (VO2), 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 beta-blockers (propranolol, metoprolol or oxprenolol) 2 h prior to each test for a total of 15 exercise tests. VO2 was measured breath-by-breath, HR was sampled once per breath, and La- was obtained every minute. Linear regression analysis was applied to VO2 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 beta-blockade. TLT for HR was significantly affected by beta-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. VO2 kinetics assessed by TLT were not significantly affected by beta-blockade. This slope of the VO2 vs work rate relationship was significantly less than placebo only at the highest dose of beta-blocker. The LSI was not significantly affected by beta-blockade. In contrast with the clear impairment of HR response to exercise during beta-blockade, both the VO2 and La- responses appear to be relatively unaffected by beta-blockade during ramp exercise tests.(ABSTRACT TRUNCATED AT 250 WORDS)
Hughson
R L
RL
Department of Kinesiology, University of Waterloo, Ontario, Canada.
D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007773:Lactates / Q000097:blood*; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D010096:Oxprenolol / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects*; D005082:Physical Exertion; D011433:Propranolol / Q000494:pharmacology
D000319:Adrenergic beta-Antagonists; D007773:Lactates; D010096:Oxprenolol; D011433:Propranolol; D008790:Metoprolol