Chest
Volume 128, Issue 4, October 2005, Pages 2159-2165
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Clinical Investigations SLEEP
A New Method of Negative Expiratory Pressure Test Analysis Detecting Upper Airway Flow Limitation To Reveal Obstructive Sleep Apnea

https://doi.org/10.1378/chest.128.4.2159Get rights and content

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 ( V˙) followed by a short-lasting V˙ drop (Δ V˙), reflecting upper airway collapsibility.

Purpose

This 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.

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 H2 O and – 10 cm H2 O in sitting and supine positions.

Results

Δ 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.

Conclusions

OSA 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.

Section snippets

Materials and Methods

Thirty-seven male subjects referred to our sleep laboratory for suspected OSA syndrome after evaluation of spirometry to exclude subjects with bronchial obstruction were recruited for the study. Mean ± SD age was 46 ± 11 years, and mean body mass index (BMI) was 34 ± 7 kg/m2. None of the subjects had acute or known chronic cardiopulmonary or neuromuscular diseases. Each patient gave informed consent, and the study protocol was approved by the local scientific committee. All subjects underwent

Results

All subjects had normal forced expiratory flow volume loops (FVC and FEV1 of 101 ± 12% of predicted and 100 ± 12% of predicted, respectively). Nocturnal monitoring showed an AHI of 51 ± 32 events/h in the whole population studied. Most subjects were obese (BMI range, 27 to 59 kg/m2), and 10 of them had BMI > 35 kg/m2. Table 1 shows anthropometric and respiratory characteristics of subjects with BMI < 35 kg/m2 and with BMI > 35 kg/m2.

NEP application during tidal expiration produced an

Discussion

The main finding of the present study is that, to assess upper airway flow limitation in a population attending a sleep center for suspected OSA, the NEP test is more usefully evaluated by Δ V˙ (% V˙ peak) than by EFL (%Vt). In fact, Δ V˙ (% V˙ peak) was better correlated to AHI than EFL (%Vt). In addition, Δ V˙ (% V˙ peak) was always correlated with AHI in the group with BMI < 35 kg/m2, while EFL (%Vt) showed some correlations with AHI, mostly when severely obese

Acknowledgment

The authors wish to thank Dr. Pietro Abate for his help and Mr. Giovanni Sciortino for technical support.

REFERENCES (25)

  • FlemonsWW et al.

    Clinical prediction of the sleep apnea syndrome

    Sleep Med Rev

    (1997)
  • FogelRB et al.

    Sleep: II. Pathophysiology of obstructive sleep apnoea/hypopnoea syndrome

    Thorax

    (2004)
  • Cited by (0)

    This study was supported by the Italian National Research Council.

    Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

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