Correlation of nonspecific bronchial responsiveness to baseline pulmonary function in patients with asthma and sinobronchial syndrome.

To examine the relationship of nonspecific bronchial responsiveness to baseline pulmonary function, and to compare the reactivity in asthma and sinobronchitis, we measured the provocative concentration of methacholine, causing a 20% fall in forced expiratory volume in one second (PC20-FEV1) in 82 asthmatic patients, 54 patients with sinobronchial syndrome and 57 normal subjects. Log PC20-FEV1 was directly correlated to baseline pulmonary function. The strongest correlation was seen between log PC20-FEV1 and baseline FEV1 as a % of the predicted FEV1 (%FEV1), both in asthma (log PC20-FEV1 = 0.020 x %FEV1-1.988, r = 0.54, p < 0.01) and in sinobronchial syndrome (log PC20-FEV1 = 0.025 x %FEV1-1.233, r = 0.64, p < 0.01). From the regression equations, the mean value of PC20-FEV1 at 100% FEV1 was calculated as 1.02 and 18.5 mg/ml in asthmatic and sinobronchitic patients, respectively, and the value was 35.5 mg/ml in normal subjects. The PC20-FEV1 to %FEV1 relationship may be helpful to assess individually measured PC20-FEV1 values in patients with airway obstruction.