Time-dependent effect of sectioning carotid sinus nerves on the vagally mediated baroreflex.

The purpose of the reported experiments was to examine whether the vagally mediated baroreflex system (V-system) increases its feedback gain with time after sectioning of the carotid sinus nerves (CSN). In 10 dogs anesthetized with Nembutal, we determined the overall open-loop gain (G) of the rapidly acting arterial pressure control system. G was assessed as (delta API/delta APs)-1, where delta API and delta APs represent the immediate and steady-state decreases in arterial pressure at the aortic arch following a fast step-wise reduction in blood volume. delta API, delta APs and GINTACT in the intact condition (30th min before sectioning of the CSN) were -1.8 +/- 0.1 kPa, -0.20 +/- 0.01 kPa and 8.4 +/- 0.3 (mean +/- SE), respectively. The mean values of delta API, delta APs and G after sectioning of the CSN (Gv), first averaged within individual dogs and then averaged for ten dogs, were -2.53 +/- 0.07 kPa, -1.1 +/- 0.05 kPa, and 1.5 +/- 0.1, respectively. Gv did not change with time over about 4 h after sectioning of the CSN. It is concluded that the V-system cannot augment its ability to restore arterial pressure in compensation for the lost function of the carotid sinus baroreflex system over 4 h after sectioning of the CSN in the anesthetized dog.