A new method using quick hemorrhage allowed estimation of the overall open-loop gain of the arterial pressure control system under closed-loop conditions without surgically opening the reflex loop.
We developed a method to estimate an overall open-loop gain of the arterial pressure control system without surgically opening the reflex loop. Dogs anesthetized by intravenous injection of Nembutal (35 mg/kg body wt) were bled by 2 ml/kg body wt within 2-3 s through a catheter inserted into the abdominal aorta. Arterial pressure change after the quick hemorrhage was monitored via a catheter placed in the aortic arch for more than 2 min. The overall open-loop gain of the lumped arterial pressure control system was assessed as (delta API/delta APs)-1, where delta API is the immediate fall and delta APs the steady-state fall in mean arterial pressure obtained by a filter with a 2-s time constant. The advantage of this method is that the overall open-loop gain can be estimated under the closed-loop condition in which the baroreceptor reflexes operate naturally around the existing range of systemic arterial pressure. This enables one to study time-varying characteristics of the reflex gain. The disadvantage is that the substantial constituents of the lumped reflex system remain to be confirmed.
Hosomi et al. (1981) studied this question. Quick hemorrhage was evaluated on Overall open-loop gain of the lumped arterial pressure control system. A new method using quick hemorrhage allowed estimation of the overall open-loop gain of the arterial pressure control system under closed-loop conditions without surgically opening the reflex loop.