Progressive attenuation of the carotid baroreflex control of blood pressure and heart rate during exercise.

With the use of a variable pressure neck chamber, the effect of supine bicycle exercise on the carotid baroreceptor reflex was investigated in 10 normal volunteers who were studied at rest and during moderate and severe exercise, i.e., at 33% and 66% of their previously determined maximal exercise capacity. Deactivation of the carotid baroreceptors by a decrease in carotid transmural pressure produced a greater (p less than 0.001) increase in mean intra-arterial pressure at rest (+11.2 +/- 0.2 [SE] mm Hg) than during moderate (+9.0 +/- 0.2 mm Hg) and severe (+6.1 +/- 0.1 mm Hg) exercise. Heart interval decreased less (p less than 0.005) at rest (-73 +/- 3.2 msec) than during exercise (-0.7 +/- 0.7 msec and -4.6 +/- 0.2 msec, respectively). Furthermore, activation of the carotid baroreceptors by an increase in carotid transmural pressure provoked a greater (p less than 0.005) reduction in mean intra-arterial pressure at rest (-11.5 +/- 0.2 mm Hg) than during exercise (-9.8 +/- 0.1 mm Hg and -7.5 +/- 0.1 mm Hg, respectively), while the lengthening of heart interval was also more (p less than 0.005) pronounced at rest (+97 +/- 4.3 msec) than during moderate (+44 +/- 1.2 msec) and severe (+7.6 +/- 0.3 msec) exercise. Finally, carotid baroreceptor sensitivity was defined as the slope of the changes in blood pressure and heart interval that occurred with increasing (baroreceptor deactivation) and decreasing (activation) neck tissue pressure. On average, baroreceptor sensitivity was consistently smaller (p less than 0.05) during exercise, as compared to rest.(ABSTRACT TRUNCATED AT 250 WORDS)