Measurement of response to methacholine inhalation challenge in asthma and allergic rhinitis. PC20 or PC35FEV1?

It has been widely accepted that significant bronchial responsiveness is demonstrated by a 20% fall in the FEV1 during the course of a methacholine challenge (PC20 or PD20FEV1). However, many subjects with allergic rhinitis may have a positive reaction, as evidenced by attaining a PC20 or PD20FEV1, and then demonstrate a plateau. When the PC35FEV1 is used, individuals with this plateau versus individuals with asthma can clearly be differentiated. We thus decided to assess bronchial responsiveness to methacholine with PC20 and PC35FEV1 in asthmatics and patients with allergic rhinitis. Bronchial challenge with methacholine by the method described by Cockcroft et al., with a Hudson 1720 nebulizer (output: 0.198 +/- 0.017 ml/min) was performed on 57 asthmatics and on 56 patients with allergic rhinitis. At the time of the study, they had an FEV1 and FVC greater than or equal to 80% of their predicted normal value and a FEV1FVC% greater than or equal to 70%. Results were expressed as the provocative concentration of methacholine required to produce a 20% and 35% fall in FEV1 (PC20 and PC35FEV1). A plateau was considered if 3 or more consecutive doses of methacholine produced no fall in FEV1 greater than 5%. By the PC20FEV1, bronchial responsiveness was increased (PC20 less than or equal to 18 mg/ml) in 98% of patients with bronchial asthma and in 28% of patients with allergic rhinitis. By the PC35FEV1, bronchial hyperexcitability (PC35FEV1 less than or equal to 40 mg/ml) was detected in 93% of patients with bronchial asthma and in 12% of patients with allergic rhinitis.(ABSTRACT TRUNCATED AT 250 WORDS)