EFFECTS OF INSPIRED GAS ON SLEEP-RELATED APNEA IN THE RAT

Central apneas have been reported to occur in the rat during all stage s of sleep. Two types of apnea have been described: spontaneous and po stsigh, which are immediately preceded by an augmented breath. We stud ied the effect of inspired gas on the number and type of apneas in nin e adult mate Sprague-Dawley rats that were surgically prepared with co rtical electroencephalogram and nuchal electromyogram electrodes. In a ddition to the electroencephalogram and electromyogram, we recorded re spiration by the barometric method by using a single-chamber plethysmo graph. Each rat was recorded from 1000 until 1600 on 4 separate days b y using different inspired gases: room air, 100% O-2, 15% O-2, and 5% CO2. We found that the sleep-related apnea index was significantly hig her during 100% O-2 compared with room air (P < 0.05) and was signific antly lower during 15% O-2 and 5% CO2 compared with room air (P < 0.05 ). Postsigh apneas occurred more frequently than did spontaneous apnea s (P < 0.0001). The coupling between sighs and apneas was strengthened by hyperoxia and weakened by hypoxia and hypercapnia (P < 0.05 for ea ch). We conclude that stimulation of chemoreceptors acts to oppose apn ea in the rat.