Background: Expiratory 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 (V̇) followed by a short-lasting V̇ drop (ΔV̇), reflecting upper airway collapsibility.
Purpose: This study investigated if a new NEP test analysis on the transient expiratory ΔV̇ after NEP application for detection of upper airway V̇ limitation is able to identify obstructive sleep apnea (OSA) subjects and its severity.
Methods: Thirty-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 H2O and – 10 cm H2O in sitting and supine positions.
Results: ΔV̇ (percentage of the peak V̇ [%V̇peak]) was better correlated to apnea-hypopnea index (AHI) than the EFL measured as V̇, during NEP application, equal or inferior to the corresponding V̇ 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 ΔV̇ (%V̇peak) in both sitting and supine positions at both NEP pressures.
Conclusions: OSA severity is better related to ΔV̇ (%V̇peak) than EFL (%Vt) in subjects referred to sleep centers. ΔV̇ (%V̇peak) can be a marker of OSA, and it is particularly useful in nonseverely obese subjects.