The relationship between exercise capacity and different functional markers in pulmonary rehabilitation for COPD

The relationship of functional parameters such as lung mechanics, chest kinematics, metabolism and peripheral and respiratory muscle function with the level of exercise tolerance remains a controversial subject. While it has been previously shown that pulmonary rehabilitation is capable of improving exercise tolerance in patients afflicted by COPD, as expressed by values of 6-minute walking test (6MWT), the degree of contribution to this change by each of the aforementioned parameters remains unclear.

To investigate the correlation between changes in exercise capacity and other functional markers following pulmonary rehabilitation in COPD and to determine which parameters are more closely related to improvements of exercise tolerance.

Three hundred and twenty-seven patients with COPD (with average, 95% CI for forced expiratory volume in the first second [FEV₁]: 45% [25%-83%] predicted, age: 64 [48-80] years, and BMI: 27 [13.5-40.4] kg/m²) participated in this study. Thirty percent of the patients had pulmonary hypertension as comorbidity. Patients underwent a pulmonary rehabilitation program with 20-30 minutes sessions two to three times per day for 4 weeks. The program was composed of chest wall-stretching, controlled breathing exercises, and a personalized training schedule for cycling and treadmill use. Measurements of 6MWT, lung function, chest wall expansion, grip strength, maximal inspiratory pressure, and breath holding time were taken. The Body mass index, airflow Obstruction, Dyspnea and Exercise capacity (BODE-index), body mass index [BMI], FEV₁, 6MWT, modified Medical Research Dyspnea Scale score, and an alternative scale score (for BMI, FEV₁, 6MWT, and COPD Assessment Test) were calculated.

Rehabilitation resulted in a generalized improvement in 6MWT among patients (average: 360 [95% CI: 178-543 m] vs average: 420 [95% CI: 238-601 m], p<0.05). Improvements in exercise tolerance were found to be most closely associated with changes in composite BODE-index (R²=-0.6), Alternative Scale (R²=-0.56), dyspnea score (modified Medical Research Dyspnea Scale R²=-0.54), and health status (COPD Assessment Test R²=-0.4, p<0.05). In addition, improvements in exercise tolerance were found to moderately correlate with improvements in inspiratory vital capacity (IVC, R²=0.34, p<0.05). Post-rehabilitation changes in IVC displayed a connection with grip strength (R²=0.6) and chest expansion (R²=0.48).

Enhancements in exercise tolerance had correlation with changes in IVC, BODE-index, and the new Alternative Scale. However, comprehensive assessment needs to include considerations of chest kinematics and peripheral and respiratory muscle function as well.