Diagnostic value of negative expiratory pressure for airway hyperreactivity

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 FEV(1) 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 FEV(1) 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 FEV(1) > or = 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 FEV(1), 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 FEV(1) 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 FEV(1) and airway resistance measurements.