Effects of inspired gas on sleep-related apnea in the rat

Central apneas have been reported to occur in the rat during all stages of sleep. Two types of apnea have been described: spontaneous and postsigh, which are immediately preceded by an augmented breath. We studied the effect of inspired gas on the number and type of apneas in nine adult male Sprague-Dawley rats that were surgically prepared with cortical electroencephalogram and nuchal electromyogram electrodes. In addition to the electroencephalogram and electromyogram, we recorded respiration by the barometric method by using a single-chamber plethysmograph. Each rat was recorded from 1000 until 1600 on 4 separate days by using different inspired gases: room air, 100% O2, 15% O2, and 5% CO2. We found that the sleep-related apnea index was significantly higher during 100% O2 compared with room air (P < 0.05) and was significantly lower during 15% O2 and 5% CO2 compared with room air (P < 0.05). Postsigh apneas occurred more frequently than did spontaneous apneas (P < 0.0001). The coupling between sighs and apneas was strengthened by hyperoxia and weakened by hypoxia and hypercapnia (P < 0.05 for each). We conclude that stimulation of chemoreceptors acts to oppose apnea in the rat.