Peripheral Muscles

To investigate the role of systemic oxidative stress in the reduced quadriceps endurance of patients with COPD, Koechlin and coworkers conducted a randomized, double-blind, crossover study measuring dynamic quadriceps endurance tests at 40% of maximal strength after oral treatment with either the antioxidant N-acetylcysteine or placebo. Venous blood was sampled before and immediately after exercise, as well as 6 hours later. Endurance time improved by 25% after N-acetylcysteine treatment compared with placebo (p < 0.05). Oxidant release by stimulated phagocytes decreased after N-acetylcysteine treatment (p < 0.05). No change in the antioxidant system was observed. Lipid peroxidation, an index of oxidative stress, was significantly increased 6 hours after exercise in the placebo-treated patients' condition (p < 0.05), but not after N-acetylcysteine treatment. Advanced oxidized protein products, another index of oxidative stress, were also increased 6 hours after exercise by 139 ± 27% in the placebo group, but only by 54 ± 19% after N-acetylcysteine treatment (p < 0.05). These results suggest that oxidative stress may be involved in the reduced quadriceps endurance of patients with COPD.

To determine whether the development of quadriceps fatigue during exercise influences the response to a bronchodilator, Saey and coworkers studied 18 patients with COPD (FEV₁, 38% predicted). Compared with placebo, inhalation of ipratropium bromide (500 痢) tended to increase the time that cycle exercise was endured at a constant work rate: 440 versus 322 seconds. Nine patients developed quadriceps fatigue (a decrease in quadriceps twitch pressure of more than 15%) secondary to exercising after placebo; ipratropium did not increase endurance time in these patients despite an increase in FEV₁ of 11%. Nine patients did not develop quadriceps fatigue secondary to exercising after placebo; ipratropium increased endurance time in these patients (479 versus 249 seconds). The improvement in endurance time with ipratropium was correlated with twitch force of the quadriceps at 10 minutes after exercise preceded by placebo (r = 0.59). The authors conclude that the development of quadriceps fatigue may explain why some patients with COPD fail to increase endurance time after ipratropium. An editorial commentary by Casaburi accompanies this article.

Oxidative stress arising in exercising muscle may contribute to the peripheral muscle dysfunction of COPD. To determine whether quadriceps exercise induces oxidative stress and whether the stress decreases muscle endurance, Couillard and coworkers studied 12 patients with COPD (FEV₁, 33% predicted) and 10 healthy subjects. Biopsies of the vastus lateralis were obtained before and 48 hours after exercise. Quadriceps endurance was less in the patients than in the control subjects: 378 versus 843 seconds. At 48 hours, patients, but not the control subjects, displayed increases in muscle lipid peroxidation and oxidized protein; the control subjects, but not the patients, displayed an increase in peroxidase glutathion activity. Endurance time was inversely correlated with both muscle lipid peroxidation (r = -0.66) and oxidized protein (r = -0.70). The authors conclude that quadriceps exercise increased oxidative stress but not antioxidant activity in patients with COPD, and that the increase in oxidative stress was correlated with a decrease in quadriceps endurance.

To determine whether severity of COPD influences the degree of quadriceps fatigability after single muscle contractions, Mador and coworkers studied 8 patients with severe COPD (FEV₁, 26% predicted), 11 patients with mild-to-moderate COPD (FEV₁, 50% predicted), and 10 healthy subjects. Maximum voluntary contraction of the right quadriceps achieved a force of 44 kg in patients with severe COPD, 49 kg in patients with mild-to-moderate COPD, and 58 kg in healthy subjects. Three sets of 10 maximum voluntary contractions of the quadriceps achieved greater fatigability (measured as the decrease in potentiated twitch force during magnetic stimulation of the femoral nerve) of the quadriceps in patients with severe COPD than in patients with mild-to-moderate COPD or the healthy subjects. The fall in twitch force in patients with mild-to-moderate COPD was not significantly different from healthy subjects. The authors conclude that patients with severe COPD display greater fatigability of the quadriceps muscle than do healthy subjects or patients with mild-to-moderate COPD.

When cycling, patients with COPD often stop because of leg effort rather than dyspnea. To determine whether the response might differ when patients walk versus when they cycle, Man and coworkers studied 84 patients with COPD (FEV₁, 41% of predicted). Dyspnea alone was a more common limiting symptom during incremental walking than during incremental cycling (81 versus 34%) and during endurance walking than during endurance cycling (75 versus 29%). Twitch stimulation of the quadriceps was performed in 12 of the patients. Walking did not decrease twitch tension of the quadriceps, whereas cycling caused a 17.1% decrease in twitch tension. The authors conclude that leg effort and fatigue of the quadriceps are infrequent after walking in patients with COPD.

Citations 1-6 of 6 total displayed.

Does Oxidative Stress Alter Quadriceps Endurance in Chronic Obstructive Pulmonary Disease?

Christelle Koechlin, Annabelle Couillard, David Simar, Jean Paul Cristol, Hélène Bellet, Maurice Hayot, and Christian Prefaut
Am. J. Respir. Crit. Care Med. 169: 1022 -1027. First published online as doi:10.1164/rccm.200310-1465OC [Abstract] [Full text]

Symptoms and Quadriceps Fatigability after Walking and Cycling in Chronic Obstructive Pulmonary Disease

William D.-C. Man, Mohamed G. G. Soliman, Johanne Gearing, Sheena G. Radford, Gerrard F. Rafferty, Barry J. Gray, Michael I. Polkey, and John Moxham
Am. J. Respir. Crit. Care Med. 168: 562 -567. First published online as doi:10.1164/rccm.200302-162OC [Abstract] [Full text]

Limitation to Exercise Tolerance in Chronic Obstructive Pulmonary Disease: Look to the Muscles of Ambulation

Richard Casaburi
Am. J. Respir. Crit. Care Med. 168: 409-410. [Full text]

Contractile Leg Fatigue after Cycle Exercise: A Factor Limiting Exercise in Patients with Chronic Obstructive Pulmonary Disease

Didier Saey, Richard Debigaré, Pierre LeBlanc, M. Jeffery Mador, Claude H. Côté, Jean Jobin, and François Maltais
Am. J. Respir. Crit. Care Med. 168: 425 -430. First published online as doi:10.1164/rccm.200208-856OC [Abstract] [Full text]

Quadriceps Fatigability after Single Muscle Exercise in Patients with Chronic Obstructive Pulmonary Disease

M. Jeffery Mador, Omer Deniz, Ajay Aggarwal, and Thomas J. Kufel
Am. J. Respir. Crit. Care Med. 168: 102 -108. First published online as doi:10.1164/rccm.200202-080OC [Abstract] [Full text]

Exercise-induced Quadriceps Oxidative Stress and Peripheral Muscle Dysfunction in Patients with Chronic Obstructive Pulmonary Disease

Annabelle Couillard, François Maltais, Didier Saey, Richard Debigaré, Annie Michaud, Christelle Koechlin, Pierre LeBlanc, and Christian Préfaut
Am. J. Respir. Crit. Care Med. 167: 1664 -1669. First published online as doi:10.1164/rccm.200209-1028OC [Abstract] [Full text]

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