Chemoreceptor stimulation interferes with regional hypoxic pulmonary vasoconstriction.

Hypoxemia interferes with the diversion of blood flow away from hypoxic regions of the lung, possibly through activation of the arterial chemoreceptor reflex. The purpose of this study was to determine if selective stimulation of carotid chemoreceptors reduces the diversion of flow (hypoxic vasoconstriction) when normal systemic oxygen levels are present. Chloralose anesthetized dogs were paralyzed and each lung was separately ventilated via a dual-lumen endobronchial tube. Left pulmonary artery (QL) and main pulmonary artery (QT) blood flows were measured with electromagnetic flow probes. Chemoreceptors were stimulated by perfusion of the carotid sinuses with hypoxic, hypercapnic blood. QL/QT averaged 46 +/- 4, 29 +/- 2, and 36 +/- 4% during bilateral O2 ventilation (control), left lung N2 ventilation, and left lung N2 plus chemoreceptor stimulation in dogs treated with the cyclo-oxygenase inhibitor meclofenamate. After vagotomy, QL/QT averaged 45 +/- 4, 27 +/- 3, and 28 +/- 2% during the same conditions. QL/QT decreased significantly from control (P less than 0.05) during left lung N2 alone but did not decrease during left lung N2 plus chemoreceptor stimulation in dogs with intact vagi. In contrast, QL/QT decreased significantly both before and during chemoreceptor stimulation in vagotomized dogs. The same responses were observed in dogs not treated with meclofenamate. These results indicate that selective stimulation of arterial chemoreceptors can interfere with regional hypoxic vasoconstriction and suggest that the vagus nerves may mediate this effect.