UPPER AIRWAY COOLING REDUCES UPPER AIRWAY-RESISTANCE IN ANESTHETIZED YOUNG GUINEA-PIGS

In adults, the upper airway (UA) contains a variety of receptors inclu ding cold receptors, which evoke reflex effects on ventilation and UA dilator muscle activity, which may be important in the regulation of U A patency. However, very little is known about UA receptors in young a nimals, and the effects of UA cooling on UA dilator muscle activity an d resistance have not been studied. A constant flow of warm or cool ai r was applied to the isolated UA in anaesthetized, vagotomized young g uinea-pigs breathing spontaneously through a low-cervical tracheostomy while ventilation, UA resistance and geniohyoid muscle electromyograp hic activity were recorded, Cooling caused an inhibition of breathing, a reduction in UA resistance and an excitation of geniohyoid muscle a ctivity, Topical anaesthesia of the UA or sealing the nose and cutting the superior laryngeal and glossopharyngeal nerves abolished the vent ilatory and geniohyoid muscle responses but not the fall in UA resista nce, It is concluded that upper airway cooling reflexly inhibits breat hing and excites geniohyoid muscle activity, Cooling also reduces uppe r airway resistance by an effect which is not of reflex origin, possib ly by reducing upper airway mucosal blood flow.