Effects of exercise on heart output of the dog

Abstract

Effects of varying rates of work on the heart output of healthy young dogs were determined by the direct Fick method. Blood was sampled simultaneously through a polyethylene catheter in the right ventricle and an inlying needle in the left carotid artery. Heart rates were determined from right ventricular pressure recordings. Oxygen consumption was determined by the open-circuit method. Oxygen consumption of the dog was linearly related to work rate in runs on the treadmill at 5.6, 9.6 and 12.9 km/hr. up an 18% grade. Minute volume of the heart, arteriovenous oxygen difference, heart rate and stroke volume were found to increase with increasing metabolic rate. The average stroke volume in the hardest work rate was 82% greater than the average resting value. An animal whose activity had been greatly restricted for 3 months showed a 62% increase in stroke volume from rest to running on the treadmill at 9.6 km/hr. up an 18% grade. The data show that a substantial increase in stroke volume in work must necessarily occur in order to account for the observed increase in minute volume. Submitted on May 10, 1960