Respiratory-related quality of life: Relation to pulmonary function, functional exercise capacity, and sputum biophysical properties

One of the difficulties in assessing mucoactive therapy is selecting clinic al outcome variables that reflect the impact of clearing airway secretions on quality of life (QOL). Petty and colleagues developed a questionnaire de signed to evaluate the clinical impact of mucoactive therapy in patients wi th chronic bronchitis (CB). We evaluated this questionnaire in a multicente r study of a mucolytic medication used in patients with CB and hypothesized that spirometry, exercise capacity, and sputum clearability changes would correlate with QOL changes. This was a multicenter trial in 159 patients wi th stable CB (111 completed the 16-week study). Spirometry, plethysmography , the 6-minute walk test (6MWT), and Petty score as a measure of QOL were a ssessed at each visit. Sputum was collected at each visit. Cough transporta bility was measured in a cough machine, and mucociliary transportability wa s measured on the frog palate. Cohesivity was measured in a filancemeter, i nterfacial tension by de Nouy ring, and wettability by contact angle analys is. Within the entire data set of 694 evaluations, there was no correlation between pulmonary function and QOL. There was an inverse correlation with distance covered in a 6MWT (R-2 = 0.041, p < 0.0001). Sputum CTR was direct ly correlated with QOL (R-2 = 0.027, p < 0.0001). Change from baseline (mea n of first three visits) was computed and compared the change in the mean o f values at the 8- and 12-week visits (n = 108 sets of data pairs). This wa s analyzed as a percentage of change for continuous measurements, and as QO L is normative, we calculated the absolute change in QOL. There was no rela tion between QOL and 6MWT changes. There was an inverse relation between ch ange in forced expiratory volume in 1 second and QOL (R-2 = 0.092, p = 0.00 21) as well as between forced vital capacity and QOL (R-2 = 0.05, p = 0.024 ). There was a direct relation between CTR and QOL (R-2 = 0.039, p = 0.048) . The relation between QOL and 6-minute walk distance was expected but weak . The consistent relation between CTR and QOL (suggesting that improved CTR of sputum is associated with decreased QOL) is difficult to explain. A cha nge in forced expiratory volume in 1 second and forced vital capacity did c orrelate with a change in QOL. There is a need for a good QOL tool to evalu ate mucus clearance devices or medications. The Petty questionnaire was des igned specifically for this task, but the effect on sputum properties by cu rrent mucoactive agents may be too small to elicit a significant change in the Petty score.