Static versus dynamic techniques for characterizing the carotid sinus baroreceptor reflex in conscious rabbits.

Abstract

1. We have studied in conscious rabbits the dynamic (AC) characteristics of the carotid sinus baroreceptor reflex by effecting sinusoidal pressure changes across the all of the carotid sinus of 28, 55 and 103 mmHg amplitude at frequencies of 0.005, 0.01 and 0.01 Hz. 2. The amplitudes of the reflex oscillations of blood pressure and heart rate were dependent on both input frequency and amplitude. The output amplitude for blood pressure was maximal at 0.005 Hz, for heart rate at 0.02 Hz: i.e. blood pressure output exhibited frequency attenuation, heart rate output frequency amplification. 3. AC gain was similarly dependent on input frequency, and was inversely associated, for both blood pressure and heart rate, with input amplitude. 4. Phase lag for heart rate behind carotid transmural pressure was small (3-4 degrees), suggesting that vagal efferent mechanisms predominated. For blood pressure it was positively associated with input frequency, and was much larger (30 degrees, 19 degrees and 12 degrees). 5. The reflex was also elicited by intermittent static (DC) input. The AC and DC output amplitudes were similar at high input amplitudes, but DC gain was always greater than AC except for the case of heart rate at high input frequency and low input amplitude. 6. The AC characteristics of the reflex were satisfactorily reproducible over 2-15 days. AC output amplitude provides a measure of the performance limits of the reflex, AC gain of its capacity to buffer rapidly changing disturbances, while phase lag reflects the inertia of the reflex.