Relevance of dyspnoea and respiratory function measurements in monitoring of asthma: a factor analysis

Previous studies in patients with stable chronic obstructive pulmonary dise ase have demonstrated that objective measures (lung volumes and respiratory muscle force) and clinical or subjective measures (symptoms of breathlessn ess and exercise tolerance) are quantities that independently characterize the conditions of these patients. Such an evaluation has not been previousl y applied in patients with stable bronchial asthma. Sixty-nine patients wit h stable chronic asthma underwent evaluation of static (functional residual capacity, FRC) and dynamic [forced expiratory volume in 1 sec (FEV1) and f orced vital capacity, FVC] lung volumes; respiratory muscle strength (RMS). by measuring maximal inspiratory and expiratory pressures. and exercise ca pacity by means of the 6-min walking distance (6MWD). Chronic exertional dy spnoea was assessed by the Baseline Dyspnoea Index (BDI) focal score and by the Medical Research Council (MRC) scale. Statistical evaluation was perfo rmed by applying factor analysis. Three factors accounted for 78% of the co ral variance in the data: FEV,, FVC loaded on a factor I: RMS, FRC and 6MWD loaded on a factor II: dyspnoea ratings loaded on a factor III. Post-hoc a nalysis by randomly dividing the patients into two subgroups gave the same results. In asthmatic patients, airway obstruction appeared as an independe nt dimension or factor. Dyspnoea independently characterized the condition of asthma. Submaximal exercise tolerance could not be associated with the s ymptom of breathlessness. Evidence of independent factors support the valid ity of routine, multi-factorial assessment and the primary goal of treatmen t to alleviate symptoms and improve functional capacity in stable asthmatic s. (C) 2001 HARCOURT PUBLISHERS LTD.