Amplitude dependence of the carotid sinus reflex.

Abstract

Both carotid arteries of anesthetized mongrel dogs were perfused with arterial blood by a servo controlled peristaltic pump. This preparation allowed to examine the carotid sinus pressure reflex under open loop condition as well as under closed loop condition, without touching the receptor area. The experiments were performed before and after vagotomy. The response of the systemic arterial pressure to changes of the carotid sinus pressure was recorded and evaluated. In order to test the open loop characteristics of the system, the perfusion pressure in the carotid arteries was varied sinusoidally (0.01 to 0.2 Hz). It was found that the amplitude of the carotid sinus pressure had a marked influence on the gain of the reflex. The gain decreased with increasing amplitudes of the carotid sinus pressure at all frequencies tested. Vagotomy increased the gain especially at the low frequencies. By applying a hybrid computer system to control the perfusion pump, the same preparation could be examined under closed loop condition. Particularly, the effect of an artificial time delay (1–35 sec) between systemic and carotid sinus pressure was tested. We found that this procedure generates autooscillations of the arterial pressure. The period of the oscillations is proportional to the artificial time delay. From open loop results the closed loop behaviour of the system was calculated and compared with the actual experimental results. We could show that the amplitude dependence of the carotid sinus pressure reflex is important to explain the generation of oscillations in the closed loop system by an artificial time delay. However, whereas the predicted autooscillation frequencies agreed quite well with the experimental recordings, the prediction of the amplitudes of the oscillations showed remarkable errors, which probably are due to still unexplained nonlinearities. It can be concluded that 1) the amplitude dependence of the carotid sinus reflex is an important property of the pressure control system. 2. The application and comparison of open loop and closed loop methods in the same experiment allows to check results and predictions more thoroughly than either one of these methods alone.