Oxidative capacity of the skeletal muscle and lactic acid kinetics during exercise in healthy subjects and patients with COPD.

[Background] In patients with chronic obstructive pulmonary disease (COPD), early lactic acidosis during exercise should be considered as playing a role in the limitation of exercise tolerance. It was hypothesized that the relationship between blood lactate concentrations (LA) and tissue oxygenation index (TOI) is available for the prediction of aerobic capacity of skeletal muscle. [Methods] Changes of LA and TOI in the vastus lateralis muscle were measured during incremental cycling exercise in 12 healthy subjects and 4 patients with COPD. The relationship between TOI and LA was examined in 12 healthy subjects and 4 COPD patients, and changes in the relationship were examined at an interval of several years (3.3 +/- 1.0).
[Results] (1) From the pattern LA as related to TOI, the healthy subjects were classified into the three groups. Group A (n = 3); LA increased slowly with a decrease in TOI. Group B (n = 3); LA increased steeply after the half point of maximal exercise. Group C (n = 6); LA increased steeply before the half point of maximal exercise. (2) In 3 patients with COPD, the relationship between TOI and LA shifted rightward at the second examination.
[Conclusion] The steep increase in LA from the approximate resting value of TOI during exercise suggests that the aerobic capacity of working skeletal muscle decreased.