Cardiovascular Studies during Controlled Baroreflex Activation in the Dog: I. Effects of Enflurane

In chloralose-anaesthetized dogs the carotid sinuses were bilaterally perfused with blood from a femoral artery, either at systemic arterial pressure through a direct by-pass or with a pump in order to control the sinus pressure. Influences from cardiac receptors and aortic baroreceptors were eliminated by denervation. Administration of enflurane (1.6% end-tidal concentration) with the presence of barostatic modulation, i.e. the carotid sinuses were perfused at prevailing systemic arterial pressure, reduced cardiac performance (cardiac output, cardiac contractility, heart rate and left ventricular stroke work) and mean arterial pressure. When barostatic compensation of enflurane-induced circulatory changes was prevented by maintaining sinus perfusion pressure constant at the pre-enflurane level, these haemodynamic alterations, with the exception of cardiac output, were significantly more pronounced. Furthermore, systemic vascular resistance decreased. We conclude that barostatic reflexes significantly modify cardiovascular depressive effects of enflurane.