Clinical application of the forced oscillation technique for CPAP titration in the sleep apnea/hypopnea syndrome

We have previously demonstrated that upper airway obstruction in sleep apne a/hypopnea syndrome (SAHS) can be accurately assessed in real-time by measu ring respiratory impedance (Z) with the forced oscillation technique (FOT). The aims of the present study were: (1) to determine the feasibility of id entifying the optimal continuous positive airway pressure (CPAP) for patien ts with SAHS based on analysis of the Z signal during conventional polysomn ographic CPAP titration studies; and (2) to evaluate practical issues invol ved in the application of FOT during CPAP titration. We performed CPAP titr ation in 28 patients with SAHS during polysomnography (PSG) (14 nap and 14 full overnight studies) using a FOT system applied continuously to obtain a n on-line measurement of Z. FOT was easily implemented and was well-tolerat ed by the patients. Optimal CPAP levels were determined both in the convent ional manner from the standard PSC titration record and during a separate b linded analysis using the FOT signal alone. The mean conventional versus FO T-based optimal CPAP values were similar for both nap studies (10.6 +/- 0.6 [mean +/- SEM] versus 11.1 +/- 0.6 cm H2O, respectively, p = 0.054) and ov ernight studies (9.9 +/- 0.7 versus 9.9 +/- 0.6 cm H2O, respectively, p 1.0 0). Subsequent analysis of the PSC record with the FOT signal incorporated demonstrated that artefacts in the Zi tracing occurred during mask leak, mo uth breathing, and movement during arousal. Such abnormalities were readily identified from the flow tracing. These results indicate that, for adequat e interpretation, the tracing and values of respiratory impedance obtained by FOT should be evaluated in conjunction with the flow signal. Continuous FOT-guided CPAP titration is feasible and may be a useful adjunct during ma nual titration. FOT could also potentially serve as the basis for automated CPAP in SAHS.