Oxygen Uptake and Lactate Kinetics in Patients with Chronic Obstructive Pulmonary Disease during Heavy Intensity Exercise: Role of Pedaling Cadence.

Oxygen uptake slow component ((V) triple over dot (O2sc)) is associated with lactate accumulation, likely a contribution of poorly oxidative muscle fibers. We aimed to test the hypothesis that higher muscle tension during slow pedaling rates would yield more prominent (V) triple over dot (O2sc) in healthy subjects, but not in COPD patients. Eight severe COPD patients and 8 age-matched healthy individuals performed 4 rest-heavy exercise transitions at 40 and 80 RPM. Work rates at the two cadences were balanced. Venous blood was sampled for measurement of lactate concentration at rest and every 2 minutes until the end of exercise. <(V)over dot>(O2), kinetics were analyzed utilizing nonlinear regression. <(V)over dot>(O2), phase II amplitudes at the two cadences were similar in both groups. In healthy individuals, (V) triple over dot (O2sc) was steeper at 40 than 80 RPM (46.6 +/- 12.0 vs. 29.5 +/- 11.7 mL/min(2), p = 0.002) but not in COPD patients (16.2 +/- 14.7 vs. 13.3 +/- 7.6 mL/min(2)). End-exercise lactate concentration did not differ between cadences in either group. In healthy individuals, greater slow-cadence <(V)over dot>(O2sc) seems likely related to oxidative muscle fiber recruitment at higher muscular tension. COPD patients, known to have fast-twitch fiber predominance, might be unable to recruit oxidative fibers at high muscle tension, blunting (V) triple over dot (O2sc) response.