Effect of baroreceptor reflex stimulation on blood flow to an atelectatic lung

The effect of baroreceptor reflex stimulation by carotid sinus hypotension on the pulmonary vascular response to atelectasis was studied in eight dogs anesthetized with chloralose. Closed-chest dogs with electromagnetic flow probes previously implanted on their left (QL) and main (QT) pulmonary arteries had their left and right lungs ventilated separately. Their carotid sinuses were isolated bilaterally and perfused by a pulsatile pump with a physiological salt solution. After an initial period of bilateral 100% O2 ventilation with carotid sinus perfusion pressures (CSPP) set at each animal's initial mean arterial pressure (98 +/- 19 Torr), the left airway was occluded, QL/QT fell from 0.33 +/- 0.01 to 0.24 +/- 0.02 and PO2 fell from 323 +/- 35 Torr to 74 + 7 Torr. When CSPP was lowered to 21 +/- 3 Torr, there were no changes in QL/QT and PO2. These results suggest that stimulation of the baroreceptor reflex by carotid sinus hypotension does not interfere with the diversion of pulmonary blood flow away from a unilaterally atelectatic lung.