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Diagnostic Value of Negative Expiratory Pressure for Airway Hyperreactivity^*

^* From the Departments of Internal Medicine (Drs. P-H Kuo, Hsu, Wu, S-H Kuo, and Yang, and Miss Chang), National Taiwan University Hospital, Taipei; and The Department of Internal Medicine (Dr. Wang), Far Eastern Memorial Hospital, Taipei County, Taiwan.

Correspondence to: Ping-Hung Kuo, MD, Department of Internal Medicine, National Taiwan University Hospital, No. 7, Chung-Shan South Rd, Taipei, Taiwan; e-mail: kph{at}ntumc.org

Study objectives: To examine the value of negative expiratory pressure (NEP) in the assessment of methacholine bronchoprovocation testing (BPT).

Design: Prospective, observational study.

Setting: Pulmonary function laboratory in a university hospital.

Participants: Fifty-nine patients with chronic cough referred from outpatient clinics for methacholine BPT.

Methods: Each subject inhaled successive doubling concentrations of methacholine (from 0.049 to 25 mg/mL) until the FEV₁ decreased for > 20% or the maximum concentration of methacholine was inhaled. NEP was measured in the sitting position during tidal breathing before and after methacholine BPT. The FEV₁ and forced oscillation airway resistance (Rrs) and interrupter airway resistance (Rint) were also obtained simultaneously. A positive BPT result was defined as a fall in FEV₁ 20%.

Result: At baseline, only five patients had expiratory flow limitation as demonstrated by NEP (EFL-N). There were 39 patients with positive BPT results, and the other 20 patients had negative results. Among the BPT-positive patients, only 13 patients (33.3%) had EFL-N after methacholine challenge. The sensitivity indexes (absolute change/SD) of FEV₁, NEP, Rrs, and Rint were 16.0 ± 9.6%, 1.1 ± 1.6%, 3.8 ± 4.5%, and 5.89 ± 4.4% (mean ± SD), respectively. The percentage changes in FEV₁ in BPT-positive patients correlated with the percentage changes in Rrs (r = 0.419, p = 0.008) and only marginally with the percentage changes in Rint (r = 0.307, p = 0.058), but not with the changes in EFL-N (r = 0.048, p = 0.77).

Conclusion: These data suggest that NEP at sitting position is not sensitive in the assessment of methacholine bronchoprovocation as compared to FEV₁ and airway resistance measurements.

Key Words: forced oscillation technique • interrupter airway resistance • methacholine bronchoprovocation • negative expiratory pressure • spirometry

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