Relationship between airway responsiveness and peak expiratory flow variability in subjects with allergic rhinitis.

BACKGROUND: Previous studies have demonstrated an increase in diurnal variation of peak expiratory flow (PEF) in subjects with allergic rhinitis who had decreased methacholine PC20 values. The relationship between PEF variability and some indices of the concentration-response curve to methacholine such as the position and level of the maximal response-plateau has not been studied. OBJECTIVE: The study was carried out to determine differences in PEF variability between subjects with allergic rhinitis who showed plateaus on the concentration-response curves to methacholine at mild degrees of airway narrowing, and patients in whom no plateau was detected. METHODS: Forty-three nonasthmatic patients with allergic rhinitis were included in the study. Subjects underwent methacholine challenge tests with doubling concentrations from 0.39 to 200 mg/mL and measured their PEF three times daily for the next seven days, using mini-Wright peak flow meters. The concentration-response curves to methacholine were characterized by the threshold value (PC20 = provocative concentration required to produce a 20% fall in FEV1) and, if possible, by the position (EC50 = concentration of methacholine that produced 50% of the maximal response) and maximal response-plateau (FEV1 falls < or = 5% after at least three of the highest concentrations). The variability of PEF was expressed as the amplitude percent mean. RESULTS: No correlations were observed between amplitude percent mean and PC20 (r = -.23, NS), EC50 (r = -.07, NS), or level of plateau (r = .02, NS). The amplitude percent mean was higher in subjects who had decreased methacholine threshold values without plateau (geometric mean = 8.3%; range = 3.8% to 14.2%) than in subjects who had decreased threshold values and plateaus (geometric mean = 4.5%; range = 2.4% to 9.9%; P < .01), or subjects who had normal threshold values and plateaus (geometric mean = 4.4%; range = 1.6% to 10.8%; P < .01). Although subjects who had decreased threshold values and plateaus showed higher methacholine responsiveness than subjects with normal threshold values and plateaus (geometric mean PC20 = 6.2 mg/mL versus 107.1 mg/mL, P < .01; geometric mean EC50 = 3.1 mg/mL versus 9.1 mg/mL, P < .01; mean +/- SEM level of plateau = 17.2 +/- 1.8% versus 28.8 +/- 1.1%, P < .001), the difference in amplitude percent mean was not significant. CONCLUSIONS: The loss of plateau on the concentration-response curves to inhaled methacholine at mild degrees of airway narrowing identifies those subjects with allergic rhinitis who show a greater PEF variability. The PEF variability and airway responsiveness are not interchangeable terms.