Effect of chemoreceptor stimulation and inhibition on total pulmonary resistance in humans during NREM sleep.

We investigated the effect of chemoreceptor stimulation and inhibition on total pulmonary resistance (RL) during non-rapid-eye-movement (NREM) sleep in healthy subjects. Chemoreceptor stimulation was accomplished with brief isocapnic hypoxia (n = 8). Minute ventilation increased to 150% of room air control. RL at peak inspiratory flow decreased to 66% of room air control. Resistive pressure-inspiratory flow plots demonstrated lower resistive pressures for a given inspiratory flow. Chemoreceptor inhibition was accomplished by abruptly terminating brief hypocapnic hypoxia with 100% O2 (n = 7). Minute ventilation decreased to 63% of room air control. RL calculated at peak inspiratory or fixed flow did not change significantly, and pressure-flow plots at nadir ventilation showed no systematic change from room air control. We conclude that 1) hypoxic chemoreceptor stimulation is associated with decreased RL and enhancement of pressure-flow relationships, suggesting increased upper airway caliber; 2) upper airway patency is not compromised during periods of low ventilatory drive in normal subjects; and 3) upper airway dilating muscles and thoracic pump muscles are optionally coordinated with increased and decreased ventilatory drive.