Muscle strength as a determinant of oxygen uptake efficiency and maximal metabolic response in patients with mild-to-moderate COPD.

Objective: To compare the behavior of the oxygen uptake efficiency slope (OUES) with that of oxygen uptake at peak exertion (VO₂peak).

Methods: This was a prospective cross-sectional study involving 21 patients (15 men) with mild-to-moderate COPD undergoing spirometry, handgrip strength (HGS) testing, cardiopulmonary exercise testing, and determination of lactate at peak exertion (LACpeak).

Results: Mean weight was 66.7 ± 13.6 kg, and mean age was 60.7 ± 7.8 years. With the exception of FEV₁ and FEV1/FVC ratio (75.8 ± 18.6 of predicted and 56.6 ± 8.8, respectively), all spirometric variables were normal, as was HGS. The patients exhibited significant metabolic and hemodynamic stress, as evidenced by the means (% of predicted) for VO₂peak (93.1 ± 15.4), maximum HR (92.5 ± 10.4), and OUES (99.4 ± 24.4), as well as for the gas exchange rate (1.2 ± 0.1). The correlation between VO₂peak and OUES was significant (r = 0.747; p < 0.0001). The correlation between HGS and VO₂peak (r = 0.734; p < 0.0001) was more significant than was that between HGS and OUES (r = 0.453; p < 0.05). Similar results were found regarding the correlations of VO₂peak and OUES with MIP. Although LACpeak correlated significantly with VO₂peak (r = -0.731; p < 0.0001), only LACpeak/maximum power correlated significantly with OUES (r = -0.605; p = 0.004).

Conclusions: Our findings suggest that, in mild-to-moderate COPD, VO2 determinants other than overall muscle strength have a greater impact on OUES than on VO₂peak.