F Maltais, AA Simard, C Simard, J Jobin, P Desgagnes and P LeBlanc
Unite de Recherche, Centre de Pneumologie de l'Hopital Laval, Quebec, Canada.

Early lactic acidosis during exercise and abnormal skeletal muscle function have been reported in chronic obstructive pulmonary disease (COPD) but a possible relationship between these two abnormalities has not been evaluated. The purpose of this study was to compare and correlate the increase in arterial lactic acid (La) during exercise and the oxidative capacity of the skeletal muscle in nine COPD patients (age = 62 +/- 5 yr, mean +/- SD, FEV1 40 +/- 9% of predicted) and in nine normal subjects of similar age (54 +/- 3 yr). Following a transcutaneous biopsy of the vastus laterialis, each subject performed a stepwise exercise test on an ergocycle up to his or her maximal capacity during which 5-breath averages of oxygen consumption (Vo2), and serial La concentration measurements were obtained. From the muscle biopsy specimen, the activity of two oxidative enzymes, citrate synthase (CS) and 3-hydroxyacyl CoA dehydrogenase (HADH), and of three glycolytic enzymes, lactate dehydrogenase, hexokinase, and phosphofructokinase were determined. The La/Vo2 relationship during exercise was fitted by an exponential function in the form La = a + bvo2, where be represents the shape of the relationship. The activity of the oxidative enzymes was significantly lower in COPD than in control subjects (22.8 +/- 3.3 versus 36.8 +/- 8.6 mumol/min/g muscle for CS, and 3.1 +/- 1.1 versus 5.5 +/- 1.4 mumol/min/g for HADH, p < 0.0005) and the increase in lactic acid was steeper in COPD (b = 4.3 +/- 2.0 versus 2.1 +/- 0.2 for normal subjects, p = 0.0005). A significant inverse relationship was found between CS, HADH, and b. No difference was found between the two groups for the glycolytic enzymes. We conclude that in COPD the increase in arterial La during exercise is excessive, the oxidative capacity of the skeletal muscle is reduced, and that these two results are interrelated.

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				E. SALA, J. ROCA, R. M. MARRADES, J. ALONSO, J. M. GONZALEZ de SUSO, A. MORENO, J. A. BARBERÁ, J. NADAL, L. de JOVER, R. RODRIGUEZ-ROISIN, et al. Effects of Endurance Training on Skeletal Muscle Bioenergetics in Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., June 1, 1999; 159(6): 1726 - 1734. [Abstract] [Full Text]

				R. S. Richardson; and F. Maltais Skeletal Muscle Dysfunction vs. Muscle Disuse in Patients With COPD J Appl Physiol, May 1, 1999; 86(5): 1751 - 1752. [Full Text] [PDF]

				Pulmonary Rehabilitation---1999 Am. J. Respir. Crit. Care Med., May 1, 1999; 159(5): 1666 - 1682. [Full Text] [PDF]

				Skeletal Muscle Dysfunction in Chronic Obstructive Pulmonary Disease . A Statement of the American Thoracic Society and European Respiratory Society Am. J. Respir. Crit. Care Med., April 1, 1999; 159(4): S2 - 40. [Full Text] [PDF]

				R. S. RICHARDSON, J. SHELDON, D. C. POOLE, S. R. HOPKINS, A. L. RIES, and P. D. WAGNER Evidence of Skeletal Muscle Metabolic Reserve During Whole Body Exercise in Patients with Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., March 1, 1999; 159(3): 881 - 885. [Abstract] [Full Text]

				S. BERNARD, F. WHITTOM, P. LEBLANC, J. JOBIN, R. BELLEAU, C. BÉRUBÉ, G. CARRIER, and F. MALTAIS Aerobic and Strength Training in Patients with Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., March 1, 1999; 159(3): 896 - 901. [Abstract] [Full Text]

				D. A. OELBERG, R. M. KACMAREK, P. P. PAPPAGIANOPOULOS, L. C. GINNS, and D. M. SYSTROM Ventilatory and Cardiovascular Responses to Inspired He-O2 during Exercise in Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., December 1, 1998; 158(6): 1876 - 1882. [Abstract] [Full Text] [PDF]

				J. P. Mattson and D. C. Poole Pulmonary emphysema decreases hamster skeletal muscle oxidative enzyme capacity J Appl Physiol, July 1, 1998; 85(1): 210 - 214. [Abstract] [Full Text] [PDF]