Total airway resistance and respiratory muscle activity during sleep

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Abstract
Total airway resistance (Raw) and inspiratory muscle activity were measured in 5 normal adults during sleep. Flow was derived by electronically differentiating a volume signal obtained with a respiratory inductive plethysmograph. Esophageal and abdominal pressures were measured with a standard balloon technique and electromyograms (EMG) of the intercostal muscles and diaphragm were recorded with surface electrodes. Changes in Raw were sleep state dependent. Raw increased by a mean of 230% during non-rapid-eye-movement sleep (NREM) compared with wakefulness. During rapid-eye-movement (REM) sleep mean values were comparable to the ones measured during wakefulness. Intercostal EMG activity increased by 34% from wakefulness to NREM sleep. At the same time, transdiaphragmatic pressure (Pdi) increased by a mean of 20%, despite no change in diaphragmatic EMG activity, indicating an increase in muscle efficiency. From NREM to REM sleep diaphragmatic EMG increased by 30%, but despite the increase in diaphragmatic activity, mean Pdi values were 10% lower during this sleep state, indicating a decrease in muscle efficiency. Changes in total airway resistance, probably related to a decrease in upper airway muscle tone, lead to an increase in the work of breathing during sleep.