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(Chest. 2005;128:2159-2165.)
© 2005 American College of Chest Physicians

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

Giuseppe Insalaco, MD; Salvatore Romano, MSc; Oreste Marrone, MD; Adriana Salvaggio, MD and Giovanni Bonsignore, MD, FCCP

* From the Italian National Research Council, Institute of Biomedicine and Molecular Immunology "A. Monroy," Section of Respiratory Pathophysiology, Palermo, Italy.

Correspondence to: Giuseppe Insalaco, MD, Italian National Research Council, Institute of Biomedicine and Molecular Immunology "A. Monroy," Section of Respiratory Pathophysiology, Via Ugo La Malfa, 153–90146 Palermo, Italy; e-mail: insalaco{at}ibim.cnr.it

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 () followed by a short-lasting drop ({Delta}), reflecting upper airway collapsibility.

Purpose: This study investigated if a new NEP test analysis on the transient expiratory {Delta} after NEP application for detection of upper airway 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: {Delta} (percentage of the peak [%peak]) was better correlated to apnea-hypopnea index (AHI) than the EFL measured as , during NEP application, equal or inferior to the corresponding 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 {Delta} (%peak) in both sitting and supine positions at both NEP pressures.

Conclusions: OSA severity is better related to {Delta} (%peak) than EFL (%VT) in subjects referred to sleep centers. {Delta} (%peak) can be a marker of OSA, and it is particularly useful in nonseverely obese subjects.

Key Words: expiratory flow limitation • extrathoracic airway obstruction • negative expiratory pressure • obesity • obstructive sleep apnea • upper airway collapse






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