BRONCHIAL RESPONSIVENESS AND ACUTE BRONCHODILATOR RESPONSE IN CHRONICOBSTRUCTIVE PULMONARY-DISEASE AND DIFFUSE PANBRONCHIOLITIS

Background - Diffuse panbronchiolitis (DPB) is characterised clinicall y by chronic airflow limitation and respiratory tract infection, and p athologically by chronic bronchiolar inflammation. To elucidate the fu nctional differences between chronic obstructive pulmonary disease (CO PD) and DPB the bronchial responsiveness to methacholine was compared in 64 patients with COPD and 32 patients with DPB, and the bronchodila tor response was compared in 72 patients with COPD and 49 with DPB. Me thods - Bronchial responsiveness to methacholine was determined by the dosimeter method and expressed as PD(20)FEV(1), and bronchodilator re sponse was measured as the change in percentage predicted response wit h 5 mg nebulised salbutamol. Results - Baseline FEV(1) was similar in the two groups of patients. Patients with COPD were more responsive to methacholine than were those with DPB (geometric mean PD(20)FEV(1) 8. 87 v 48.0 cumulative units). Reversibility of air how obstruction, exp ressed as the difference between the percentage predicted postbronchod ilator FEV(1) and prebronchodilator FEV(1), was significantly larger i n patients with COPD than in those with DPB (7.87 (6.52)% v 4.16 (4.43 )%). Conclusions - The observation that patients with DPB differ subst antially in bronchial responsiveness from those with COPD is thought t o reflect the difference in the mechanisms of these two diseases that is, airway disease in DPB and more parenchymal disease in the group of patients with COPD. The nature of bronchiolar inflammation in COPD an d DPB is also different, possibly explaining the difference in bronchi al responsiveness. More fixed airflow limitation as a result of struct ural bronchiolar lesions in DPB will explain the smaller reversiblity of airflow obstruction.