Peak oxygen uptake and respiratory muscle performance in patients with chronic obstructive pulmonary disease: Clinical findings and implications

The maximal oxygen uptake (VO2max) is the gold standard measure of aerobic exercise capacity and is an important outcome measure in patients with chronic obstructive pulmonary disease (COPD). And respiratory muscle performance is also an important functional parameter for COPD patients. In addition to the traditional respiratory muscle strength test, the Test of Incremental Respiratory Endurance has recently been introduced and validated in patients with COPD. However, the relationship between VO2 and respiratory muscle performance in COPD is not well understood. Therefore, this study investigated the correlations among VO2 and respiratory muscle performance and other functional markers in COPD. A total of 32 patients with COPD were enrolled. All study participants underwent the following assessments: cardiopulmonary exercise test, pulmonary function test, respiratory muscle strength test, peripheral muscle strength test, and bioelectrical impedance analysis. When comparing VO2peak and respiratory muscle parameters, the sustained maximal inspiratory pressure (SMIP) was the only factor with a significant relationship with VO2peak. Among other functional parameters, the forced expiratory volume in one second (FEV1) showed the strongest correlation with VO2peak. It was followed by phase angle values of lower limbs, leg extension peak torque, age, and total skeletal muscle mass. When comparing respiratory muscle performance with other functional parameters, the SMIP showed the strongest correlation with hand grip strength, followed by peak cough flow, forced vital capacity, maximal inspiratory pressure, and FEV1. The results showed that the SMIP was more significantly correlated with VO2peak than the static measurement of respiratory muscle strength. This suggests that TIRE may be a useful assessment tool for patients with COPD. Additionally, FEV1 and other functional markers were significantly correlated with VO2peak, suggesting that various parameters may be used to evaluate aerobic power indirectly.