Pulmonary vascular response to carotid sinus hypotension in the awake and anaesthetized dog

The pulmonary haemodynamic response to brachiocephalic artery occlusion (BCO) was studied in nine dogs. The animals were chronically instrumented for the measurement of pulmonary artery pressure and flow together with left atrial pressure. Measurements were performed in the awake state and also at end-tidal halothane levels averaging 0.74 +/- 0.02 (H1), 0.92 +/- 0.02 (H2) and 1.13 +/- 0.03 (H3) %, with and without nitrous oxide. Halothane at any of the above concentrations, with or without nitrous oxide, had no effect on pulmonary vascular resistance compared to awake values. Most importantly, we found no evidence for active pulmonary vasomotion in response to BCO in the awake animal, or at any anaesthetic concentration.