Efficacy of Flow- vs Impedance-Guided Autoadjustable Continuous Positive Airway Pressure*: A Randomized Cross-over Trial

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Study objectives:

Autoadjustable continuous positive airway pressure (CPAP) devices are increasingly used in the treatment of obstructive sleep apnea (OSA). Since different measurements of upper airway obstruction are applied, it is uncertain whether these devices are equally effective in controlling sleep-disordered breathing. Hypothesizing that differences in therapeutic efficacy were to come out, we compared the performance of the AutoSet device (ResMed; Sydney, Australia), which features autoadjustable positive airway pressure (APAP) guided by detection of flow limitation (APAPfl), with the SOMNOsmart device (Weinmann; Hamburg, Germany), which features APAP guided by the forced oscillation technique (APAPfot).


A double-blind, randomized, cross-over trial.


The sleep disorders center and sleep laboratory of a university hospital.

Patients and interventions:

An overnight CPAP autotitration procedure was performed in 30 patients with OSA. A split-night protocol allowed that each patient used both devices.

Measurements and results:

Using polysomnography, sleep, indexes of sleep-disordered breathing, snoring, and CPAP levels were recorded. No significant differences were found in conventional sleep variables. While the apnea-hypopnea index (AHI) was lower with APAPfl (3.5 ± 5.6/h) as compared to APAPfot (9.9 ± 31.0/h), the difference was not statistically significant (mean ± SD). The snoring index, however, was significantly lower with APAPfl (35.3 ± 53.7/h vs 111.6 ± 175.4/h, respectively; p = 0.01). The median and 95th percentile pressure levels rose from wakefulness to sleep in APAPfl, but decreased in APAPfot. Higher pressure variability was present in the latter method.


These findings suggest that the APAPfl is superior to APAPfot in the control of snoring. While a lower AHI was achieved with APAPfl, at the expense of a higher median pressure but less pressure variability, the difference with APAPfot was not statistically significant.

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