Airway obstruction and chronic exertional dyspnoea in patients with persistent bronchial asthma

In patients with COPD, flow limitation (FL) predicts chronic exertional dys pnoea (CED) better than routine spirometry. Whether, and to what extent, FL and CED are overlapping quantities in chronic asthma has not yet been defi ned. Forty consecutive clinically stable asthmatic patients without smoking history or cardiopulmonary disorders, were studied. In each subject respir atory function, including static and dynamic pulmonary volumes, was evaluat ed; maximal (MEFV) and partial (PEFV) expiratory V'-V curves and isovolumic partial to maximal flow ratio (M/P). FL was assessed in a seated patient b y comparing tidal and PEFV curves; FL was detected when tidal flows were su perimposed or exceeded those obtained during PEFV curves, and was expressed as a percentage of the expired control tidal volume (V-T) affected by flow limitation (FL% V-T) Dyspnoea was assessed by both MRC scale and Baseline Dyspnoea Index (BDI) focal score. Half of the patients were found to have F L. They were older, more dyspnoeic and more obstructed (P < 0.03 - P < 0.00 0005) than the non-FL group. FEV1, vital capacity (VC), age, body mass inde x, FL and M/P ratio were all related to dyspnoea scores. FL was significant ly related to FEV1 (r = - 0.59). Multiple regression analysis showed that F EV1 (P = 0.003, r(2) = 15.3% and P = 0.004, r(2) = 20.3%) and age (P = 0.00 06, r(2) = 26.8% and P = 0.016, r(2) = 11%) independently predicted a part of the variance of MRC (P = 0.0001, r(2) = 42.1%) and BDI (P = 0.0008, r(2) = 31.3%), respectively. With dyspnoea scale being the gold standard, diagn ostic accuracy (sensitivity and specificity) by ROC (receiver operating cha racteristics) analysis was similar for FEV1 and FL. The results indicate th at FL may be present in this subset of asthmatics. CED may not be easily ex plained by abnormalities of routine spirometry or FL, the largest part of t he CED variance remained unexplained. Thus, routine spirometry, FL and CED in patients with bronchial asthma ate only partially overlapping quantities which need to be assessed separately.