MAINTAINED ABILITY OF CAROTID BAROREFLEX TO REGULATE ARTERIAL-PRESSURE DURING EXERCISE

In conscious dogs bilateral carotid occlusion increased arterial pressure by similar amounts at rest (+ 27 mmHg) and during graded exercise (+ 29 mmHg). During exercise stimulus-response curves for arterial pressure and heart rate derived from isolated carotid sinuses were displaced upward proportionately to the work load, but the curve characteristics were unchanged. After acute bilateral vagotomy similar responses to carotid occlusion were obtained at rest (+ 85 mmHg) and at 21% grade (+ 84 mmHg); the range and maximal slope of the arterial pressure stimulus-response curve during exercise was similar to that at rest, but the exercise curve was displaced downward and to the left. The carotid baroreflex was able to modulate arterial pressure as well during running as at rest. Dogs with neither carotid, aortic or cardiopulmonary receptors able to respond to the exercise stress became and remained hypotensive during mild exercise; during severe exercise hypotension was present initially, but after 90 s arterial presure recovered toward the preexercise level. Arterial and cardiopulmonary baroreceptors apparently have a major role in the support of arterial pressure in the 1st moments of exercise.