A New Method of Negative Expiratory Pressure Test Analysis Detecting Upper Airway Flow Limitation To Reveal Obstructive Sleep Apnea

BackgroundExpiratory flow limitation (EFL) by negative expiratory pressure (NEP) testing, quantified as the expiratory flow-limited part of the flow-volume curve, may be influenced by airway obstruction of intrathoracic and extrathoracic origins. NEP application during tidal expiration immediately determines a rise in expiratory flow ( V˙) followed by a short-lasting V˙ drop (Δ V˙), reflecting upper airway collapsibility.PurposeThis study investigated if a new NEP test analysis on the transient expiratory Δ V˙ after NEP application for detection of upper airway V˙ limitation is able to identify obstructive sleep apnea (OSA) subjects and its severity.MethodsThirty-seven male subjects (mean ± SD age, 46 ± 11years; mean body mass index [BMI], 34 ± 7 kg/m2) with suspected OSA and with normal spirometric values underwent nocturnal polysomnography and diurnal NEP testing at – 5 cm H2 O and – 10 cm H2 O in sitting and supine positions.ResultsΔ V˙ (percentage of the peak V˙ [% V˙ peak]) was better correlated to apnea-hypopnea index (AHI) than the EFL measured as V˙, during NEP application, equal or inferior to the corresponding V˙ during control (EFL), and expressed as percentage of control tidal volume (%Vt). AHI values were always high (> 44 events/h) in subjects with BMI > 35 kg/m2, while they were very scattered (range, 0.5 to 103.5 events/h) in subjects with BMI < 35 kg/m2. In these subjects, AHI still correlated to Δ V˙ (% V˙ peak) in both sitting and supine positions at both NEP pressures.ConclusionsOSA severity is better related to Δ V˙ (% V˙ peak) than EFL (%Vt) in subjects referred to sleep centers. Δ V˙ (% V˙ peak) can be a marker of OSA, and it is particularly useful in nonseverely obese subjects.