Effects of Atropine on Heart Rate and Oxygen Intake in Working Man

Abstract

The heart rates of 5 healthy young men were detd. during (a) rest, (b) a 16-minute walk on the treadmill at 3.5 mph. up an 8.6% grade (O2 intake 2 liters/min.), (c) an 11-min. run at 7 mph. on a level (O2 intake 3 liters/min.) and (d) an exhausting run of 5 min.'' duration (maximal O2 intake and maximal heart rate attained). In other expts. 2 mg. of atropine sulfate were administered intramusc. to each subject 53 min. before work began and heart rates and O2 intakes were measured at rest and in each of the above rates of work. At the 4 metabolic rates of the subjects in these expts. the elevations of heart rate (above corresponding controls) caused by the vagal blocking agent, atropine, were inversely related to O2 intake and, therefore, to the intensity of work stress. The maximal heart rates were unaffected by atropine. These results indicate that in men without atropine cardio-inhibitory tone is progressively decreased with increasing work stress up to the maximum, and in exhausting work with maximal heart rate vagal tone is stopped centrally. Atropine decreased maximal oxygen intake during exhausting work in all men.