LACK OF SIGNIFICANT BRONCHIAL REACTIVITY TO INHALED NORMAL SALINE IN SUBJECTS WITH A POSITIVE METHACHOLINE CHALLENGE TEST

Patients with symptoms suggestive of asthma often have normal resting pulmonary function. In these patients, a determination of airway respo nsiveness by bronchia[ challenge is useful in demonstrating bronchial hyperreactivity (BHR), a defining feature of asthma. In the methacholi ne (Mch) challenge, it is recommended that following a baseline measur ement of FEV(1), the patient inhale the normal saline (NS) diluent and FEV(1) be repeated to assess for nonspecific BHR to NS. It is also re commended that post-NS inhalation FEV(1) should be used as the control value from which decrement in FEV(1) is compared following Mch challe nge. Mch testing was performed in 44 patients with symptoms suggestive of asthma (cough, chest tightness, dyspnea) and normal resting pulmon ary function.;Baseline spirometry was obtained and repeated after inha lation of NS and,after five breaths each of Mch at the following conce ntrations: 0.025 mg/ml, 0.25 mg/ml, 2.5 mg/ml, 10 mg/ml, and 25 mg/ml. The procedure was terminated when FEV(1) decreased to at least 80% of the post-NS value or if the maximal concentration of Mch had been rea ched. The post-NS FEV(1) was greater than or equal to 91% of the pre-N S value in all the subjects (range 91-105%). Using the post-NS FEV(1) as the recommended control value, 20 patients (45%) had a positive Mch challenge and 24 patients (55%) had a negative Mch challenge. Had we used the pre-NS FEV(1) as a control value, only 2 patients would have been reclassified, and when these 2 cases are carefully examined, ther e would have been no significant change in the clinical interpretation of the MCh test. We conclude that patients with a significant BHR to Mch do not have a significant BHR to NS. However, since the NS control has been accepted as part of the standardized Mch challenge, it shoul d be included in all research studies and in most clinical Mch challen ges.