VENTILATORY AND UPPER-AIRWAY RESISTANCE RESPONSES TO UPPER-AIRWAY COOLING AND CO2 IN ANESTHETIZED RATS

The effects of upper airway (UA) cool air and CO2 on breathing and on laryngeal and supraglottic resistances were studied in anaesthetised r ats breathing spontaneously through a tracheostomy. Warm, humidified a ir containing 0, 5 and 9-10% CO2 and cool, room-humidity air were deli vered at constant flow to either the isolated larynx to exit through a pharyngotomy or to the supraglottic UA to exit through the mouth and/ or nose (nose open or sealed). Spontaneous tracheal airflow and UA air flows, temperatures and pressures were recorded. CO2 had no effect on breathing but caused a slight increase in laryngeal resistance which w as abolished by cutting the superior laryngeal nerves (SLN). Cool air caused a decrease in respiratory frequency and/or peak inspiratory flo w when applied to the isolated larynx or to the supraglottic airway wi th the nose closed. These effects were abolished by SLN section. With the nose open, the ventilatory inhibition was not abolished by SLN sec tion. Cool air also caused substantial decreases in laryngeal and supr aglottic resistances which were attenuated by SLN section and which pe rsisted following recurrent laryngeal nerve section. In conclusion, wh ilst UA cooling inhibits breathing and decreases UA resistances, UA CO 2 has minimal effects.