Evaluation of a simplified oscillation technique for assessing airway obstruction in sleep apnoea

The forced oscillation technique (FOT) is a noninvasive method that is usef ul for assessing airway obstruction and for titrating continuous positive a irway pressure (CPAP) in patients with sleep apnoea, The aim was to evaluat e the routine applicability of a simplified FOT set-up based on recording p ressure and flow at the level of the CPAP device; i,e, obviating the need f or connecting the transducers to the nasal mask. A correction to account for the tubing and the exhaust port was applied. Th is simplified FOT was evaluated on nine patients with moderate or severe sl eep apnoea during routine CPAP titration. Patient impedance measured by the simplified FOT (\Z \) was compared,vith actual patient impedance (\ Zrs \) measured simultaneously with a reference FOT based on recording pressure a nd flow at the nasal mask. An excellent agreement was found between \Z \ an d \ Zrs \ over the wide range of airway obstruction explored (4.8-72.1 cmH( 2)O .s .L-1): \Z \=\ ZrS \ X 0.86+1.3 cmH(2)O .s .L-1 (r= 0.99). Moreover, the simplified and the conventional FOT settings detected the same respirat ory events during sleep. These results demonstrate that this simplified FOT is applicable for measur ing airway obstruction during routine sleep studies in patients with sleep apnoea.