Sleep and the ventilatory response to resistive loading in normal men.

Since upper airway resistance is known to increase during sleep, inadequate resistive load compensation may contribute to the normal decline in sleeping ventilation. We determined the acute and sustained (4 min) ventilatory response to a range of external inspiratory resistive loads (4, 8, 12, and 25 cmH2O.l-1.s) during wakefulness and non-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep in seven normal men. We found that minute ventilation (VI) was well maintained with acute and sustained resistive loading during wakefulness. Immediate adjustments in ventilatory timing (prolongation of inspiratory duration) provided full compensation for airflow reduction. In marked contrast, resistive load application during NREM sleep invariably produced a significant (P less than 0.05) reduction in VI with progressively larger resistive loads producing progressively greater ventilatory decrements. This decline in ventilation was a product of a falling inspiratory flow rate with inadequate prolongation of inspiratory duration (TI). The largest decrements in ventilation occurred immediately after load application followed by partial ventilatory recovery, which occurred over time in concert with rising PCO2 and augmented ventilatory effort (as reflected by P0.1 or mouth occlusion pressure). Similar observations were made during REM sleep, although the responses were less consistent and fewer data were obtained. These observations support the hypothesis that poor load compensation for increased upper airway resistance contributes to the hypoventilation characteristic of normal sleep.