Response of nasal airway resistance to hypercapnia and hypoxia in the dog.

Nasal airway resistance was calculated in 9 anesthetized mongrel dogs by measuring the pressure difference across the nasal airway while a continuous flow of humidified air was passed through the upper airway. Hypercapnia produced a significant decrease in nasal airway resistance (P less than 0.05, Wilcoxon signed-rank test), which was proportional to the Paco2 over the range of 40 to 70 torr. Hypoxia produced a decrease in nasal airway resistance only when there was severe depression of Pao2. Direct stimulation of peripheral chemoreceptors by intravenously administered NaCN (100 microgram/kg) resulted in a significant decrease in nasal airway resistance (P = 0.06, Wilcoxon signed-rank test). Interruption of the cervical sympathetic trunk bilaterally abolished or reversed the response of the nasal airway resistance to hypercapnia and to NaCN. The study indicates that the nasal airway can modify airway resistance in response to respiratory stimuli and that this reflex is mediated by the sympathetic nervous system.