EFFECT OF ROUTE OF BREATHING ON THE VENTILATORY AND AROUSAL RESPONSESTO HYPERCAPNIA IN AWAKE AND SLEEPING DOGS

1. The influence of the upper airway on the ventilatory and arousal re sponses to hypercapnia in wakefulness and sleep was investigated using a chronic animal model. 2. Experiments were performed in five unrestr ained dogs trained to sleep naturally in the laboratory. The animal re breathed through a chronic tracheostoma (thus excluding the upper airw ay from the breathing circuit), or through the snout (intact upper air way). Resistance to breathing and volume of dead space during quiet tr acheal breathing were matched to those in quiet nasal breathing during wakefulness and sleep. CO2 rebreathing tests were performed during wa kefulness, rapid eye movement (REM) and non-REM (NREM) sleep, during n asal and tracheal breathing. 3. The ventilatory response to hypercapni a was significantly lower in nasal breathing compared with tracheal br eathing, in all behavioural states. This was due to a smaller tidal vo lume and lower breathing frequency. 4. The ventilatory response to CO2 was lowest during REM sleep, irrespective of route used for breathing . 5. Alveolar partial pressure of CO2 (P(A,CO2)) level at arousal was identical in NREM nasal and tracheal rebreathing tests. Differences in P(A,CO2) levels at arousal between NREM and REM sleep were not signif icant in nasal tests and only marginally different during tracheal bre athing. 6. We conclude that nasal breathing influences the hypercapnic ventilatory response in wakefulness and sleep, and that the presence of CO2 in the upper airway does not affect arousal in NREM and REM sle ep.