Objective: To evaluate the correlation of the quality of life in patients with chronic obstructive pulmonary disease (COPD) with the lung function tests, especially the inspiratory capacity (IC).
Methods: Sixty-two stable COPD patients were enrolled between Jan. 2006 and Mar. 2007 (55 males and 7 females), with an age range of 43 - 79 (66 +/- 8) years. Lung volume, spirometry and small airway function measurements were performed in all patients. The St George respiratory questionnaire (SGRQ) score was collected. Pearson's correlation coefficients were calculated.
Results: The total score of the 62 COPD patients was 43 +/- 17. The 3 component scores were: symptoms (54 +/- 23), activity (54 +/- 19) and impact (33 +/- 20). The FEV(1) pred% was (43 +/- 13)%, FEV(1)/FVC was (52 +/- 11)%, residual volume (RV) pred% was (194 +/- 50)%, RV/total lung capacity (TLC) was (166 +/- 31)%, and IC pred% was (74 +/- 21)%. The SGRQ scores were significantly correlated with IC pred%, RV pred%, RV/TLC, FEV(1) pred%, FEV(1)/FVC and small airway function measurements (FEF(50%), FEF(25%), MMEF). The correlation coefficients between the parameters of spirometry and the total score of SGRQ were -0.336 to -0.479, while those between the parameter of small airway function and the total score of SGRQ were -0.368 to -0.411. Among all these lung function measurements, IC pred% was best correlated with the SGRQ score, and the correlation coefficients between the IC pred% and the total score and the other 3 component scores of SGRQ were -0.418 to -0.521, respectively, P < 0.05. The symptoms section score had the poorest correlation with the lung function test.
Conclusions: The lung function test results correlate with the quality of life in patients with COPD. IC pred%, together with FEV(1) pred% should be used for clinical evaluation of patients with COPD.