Baroreceptor control of regional haemodynamics during halothane anaesthesia in the dog

Regional haemodynamic control by the cardiovascular baroreceptors was examined in dogs anaesthetized with 1 + MAC halothane in oxygen (1%). The open-loop relationships between carotid sinus pressure (CSP) and regional haemodynamics in the iliac, renal, mesenteric, aortic and coeliac beds were examined before vagotomy, following vagotomy and following thoracotomy. Around the carotid sinus reflex set point, the ratio of the reflex decrease in systemic arterial pressure to an increase in CSP (reflex gain) was -0.744+/-0.089 (mean+/-SEM): the latter increased to -1.275+/-0.093 following vagotomy. Reflex resistance changes were greatest in the renal bed and least in the coeliac bed, reflecting blood flow homeostasis which was well preserved in the renal bed but minimal in the coeliac bed. Thoracotomy in the dogs in which vagotomy had been performed resulted in no significant changes in the dependent variables studied. It is concluded that, in these dogs anaesthetized with 1 + MAC of halothane, baroreceptor control of regional pressure flow relationships is well preserved.