Cardiovascular responses to various pulsatile pressures in the carotid sinus.

SCHMIDT,ROBERT M., MAMORUKUMADA,AND KIICHI SAGAWA. Curdiovascular responses to various pulsatile pressures in the carotid sinus. Am. J. Physiol. 223 (1): l-7. 1972.-To extend the knowledge of the carotid sinus reflex, we forced the isolated sinuses of anesthetized dogs with sinusoidal (pulsatile) pressures using multiple combinations of mean level, amplitude, and frequency of pulsation. The reflex responses of mean arterial pressure, cardiac output, and total peripheral resistance were analyzed at mean sinus pressures of 75, 100, 125, and 150 mm Hg, frequencies of 1, 2, 3, and 4 Hz, and peak-to-peak amplitudes of 25, 50, and 75 mm Hg. Increasing the amplitude of pulsation from 25 to 75 mm Hg while holding the frequency at 2 Hz caused moderate and proportional reductions in arterial pressure, cardiac output, and total peripheral resistance, except when the pulsatile pressure was superimposed on mean sinus pressure of 150 mm Hg. In contrast, increasing the frequency of pulsation from 1 to 4 Hz with a fixed amplitude of 50 mm Hg evoked significant responses only after vagotomy at the mean intrasinus pressure of 75 mm Hg. An example of use of the quantitative data gained by this study is discussed in relation to evaluation of the role that the reflex system plays in maintaining mean arterial pressure after a 20$& hemorrhage. We conclude from the above findings that variations of pulse pressure and particularly of heart rate in the physiological range have relatively little reflex effect compared with that of the change in mean intrasinus pressure.