Cardiovascular Performance of Alaska Sled Dogs during Exercise

Abstract

Radiotelemetry was used to study regional blood flow distribution in Alaska sled dogs during cross-country runs. Doppler ultrasonic flowmeter transducers were chronically implanted on the coronary, renal, and mesenteric arteries, terminal abdominal aorta, and ascending aorta or pulmonary artery, and a miniature blood pressure gauge was installed in the aorta or carotid artery. Flow and pressure data telemetered from dogs running on the trail were received and recorded remotely. The heart rate, 40 to 60/min in sleeping dogs, increased to 80 to 100/min when the dogs were ambulatory and to 100 to 150/min when the dogs were excited before a race. Heart rate accelerated to 300/min at the start of exercise and commonly remained at that level throughout prolonged runs. Aortic blood pressure averaged 130/90 mm Hg at rest, but the systolic pressure often exceeded 300 mm Hg when the dogs were running. A transient drop in mean pressure occurred at the onset of running, but mean pressure during sustained exercise was practically identical to that at rest. Flow in the terminal aorta increased 9 to 12 times and coronary flow 5 to 6 times, but mesenteric and renal flows were unchanged during violent, prolonged exercise. These findings contrast with diminished visceral flows recorded in exercising humans and suggest that compensatory redistribution of flow is not a significant reserve mechanism in these animals during exercise.