Upper airway cooling reduces upper airway resistance in anaesthetized young guinea-pigs.

In adults, the upper airway (UA) contains a variety of receptors including cold receptors, which evoke reflex effects on ventilation and UA dilator muscle activity, which may be important in the regulation of UA patency. However, very little is known about UA receptors in young animals, and the effects of UA cooling on UA dilator muscle activity and resistance have not been studied. A constant flow of warm or cool air was applied to the isolated UA in anaesthetized, vagotomized young guinea-pigs breathing spontaneously through a low-cervical tracheostomy while ventilation, UA resistance and geniohyoid muscle electromyographic activity were recorded. Cooling caused an inhibition of breathing, a reduction in UA resistance and an excitation of geniohyoid muscle activity. Topical anaesthesia of the UA or sealing the nose and cutting the superior laryngeal and glossopharyngeal nerves abolished the ventilatory and geniohyoid muscle responses but not the fall in UA resistance. It is concluded that upper airway cooling reflexly inhibits breathing and excites geniohyoid muscle activity. Cooling also reduces upper airway resistance by an effect which is not of reflex origin, possibly by reducing upper airway mucosal blood flow.