Abstract
OBJECTIVES: To examine whether the lactate kinetics during exercise are abnormal in patients with chronic obstructive pulmonary disease (COPD) and to evaluate the relationship of lactate kinetics with functional status.POPULATION: Fifty-four patients with COPD (forced expiratory volume in 1 s [FEV1] [mean ± SD] 36±12% predicted, range 19 to 70) and 10 healthy, age-matched normal men were included in this study.INTERVENTION: Each subject performed a stepwise exercise test up to maximal capacity during which five-breath averages of oxygen uptake (VO2) were obtained. Arterial plasma lactate (La) concentration was also measured at each one-minute exercise step. The La/VO2 relationship during exercise was fitted by an exponential function La = a + bVO2 where b represents the steepness of the relationship. Patients' functional status was classified according to the peak VO2 : more than 16 mL/min/kg and 20 mL/min/kg or less indicated mild to moderate impairment (class B, n=15); more than 10 mL/min/kg and 16 or less mL/min/kg, moderate to severe impairment (class C, n=31); and more than 6 mL/min/kg and 10 mL/min/kg or less, severe impairment (class D, n=8). An average La/VO2 relationship was constructed for each functional class with the La and VO2 data obtained from each individual at each exercise step.RESULTS: Parameter b was obtained in all normal subjects and in 46 of 54 patients with COPD. It averaged 2.66±0.47 and 4.49±1.72 in normal subjects and COPD patients, respectively (P<0.005). In 30 of 46 patients, parameter b was greater than the upper value obtained in the normal group. The rise in arterial lactate concentration during exercise became progressively greater with the worsening of functional status.CONCLUSIONS: Lactate kinetics are frequently abnormal in patients with moderate to severe COPD compared with age-matched normal subjects. Reduction in functional status from class B to D was associated with a progressively greater increase in arterial blood lactate during exercise.