Forced oscillation measurements do not affect upper airway muscle tone or sleep in clinical studies

Upper airway obstruction in the sleep apnoea/hypopnoea syndrome (SAHS) can be easily assessed by measuring respiratory impedance with the forced oscil lation technique (FOT). This methodology has been proposed as a useful clin ical tool both for the diagnosis of sleep breathing disorders and for conti nuous positive airway pressure (CPAP) titration. However, previous studies suggest that the application of high-frequency pressure oscillation to the upper airway may induce changes in the electroencephalogram (EEG) or upper airway muscle function. The effect of FOT measurements on upper airway musc le tone and EEG in clinical sleep studies was examined. Seven patients with moderate SAHS were included (age: 54 +/- 11 yrs; apnoea/hypopnoea index: 4 3 +/- 21 events(.)h(-1); body mass index: 30 +/- 2 kg(.)m(-2)). Genioglossu s surface electromyogram activity (EMGgg) and EEG signal were analysed with and without FOT application (frequency: 5 Hz and 30 Hz; peak-to-peak press ure oscillation: 1 cmH(2)O) during stable sleep. Measurements were carried out in two different situations. Step 1: applying FOT during episodes of ob structive events or flow limitation; and step 2: during prolonged periods o f normal breathing at optimal CPAP. The root mean square of EMGgg activity and fast Fourier analysis (alpha and delta bands) of the EEG signal were pe rformed. The application of FOT did not increase EMGgg activity in any of the situat ions studied. In addition, no evidence of the effects on EEG was found: alp ha/delta relationship: awake:0.70, baseline sleep:0.13, FOT(5 Hz):0.18, FOT (30 Hz):0.11. The presented results suggest that the use of forced oscillation technique over the ranges of frequency and amplitude proposed for clinical sleep stud ies does not induce changes in upper airway muscle activity and neurologica l variables in patients with sleep apnoea/hypopnoea syndrome.