Apnee ostruttive notturne e fatica diaframmatica

In patients with obstructive sleep apnea syndrome (OSAS), respiratory muscle develop inspiratory pressure that progressively increase toward the end of the occlusive phase. In order to evaluate if the respiratory muscles may fatigue during obstructive apneas, we studied six patients with OSAS during N-REM sleep. Six apneas per patient were analyzed breath by breath. We measured transdiaphragmatic pressure (Pdi) and diaphragmatic electrical activity (EMGd). The tension-time index (TTdi) was calculated from the Pdi, whereas time and spectral analysis were performed on the EMGd in order to obtain the inspiratory slope (Sl.Insp.) from the moving average and the high to low frequency ratio (H/L) from the spectral analysis. We found a progressive increase in TTdi values toward the end of the apnea; values potentially close to the fatigue threshold (TTdi>0.18) were reached at the last occluded efforts. The H/L values decreased at the beginning of the apnea, then progressively increased toward the end, thus excluding the onset of fatigue. A linear relationship was found between the H/L and the Sl.Insp. values. Our results suggest that diaphragmatic fatigue does not usually occur in OSAS and that changes in H/L are probably related to changes in neuromuscular drive.