The self-perception of dyspnoea threshold during the 6-min walk test: a good alternative to estimate the ventilatory threshold in chronic obstructive pulmonary disease.

To determine and/or adjust exercise training intensity for patients when the cardiopulmonary exercise test is not accessible, the determination of dyspnoea threshold (defined as the onset of self-perceived breathing discomfort) during the 6-min walk test (6MWT) could be a good alternative. The aim of this study was to evaluate the feasibility and reproducibility of self-perceived dyspnoea threshold and to determine whether a useful equation to estimate ventilatory threshold from self-perceived dyspnoea threshold could be derived. A total of 82 patients were included and performed two 6MWTs, during which they raised a hand to signal self-perceived dyspnoea threshold. The reproducibility in terms of heart rate (HR) was analysed. On a subsample of patients (n=27), a stepwise regression analysis was carried out to obtain a predictive equation of HR at ventilatory threshold measured during a cardiopulmonary exercise test estimated from HR at self-perceived dyspnoea threshold, age and forced expiratory volume in 1 s. Overall, 80% of patients could identify self-perceived dyspnoea threshold during the 6MWT. Self-perceived dyspnoea threshold was reproducibly expressed in HR (coefficient of variation=2.8%). A stepwise regression analysis enabled estimation of HR at ventilatory threshold from HR at self-perceived dyspnoea threshold, age and forced expiratory volume in 1 s (adjusted r=0.79, r=0.63, and relative standard deviation=9.8 bpm). This study shows that a majority of patients with chronic obstructive pulmonary disease can identify a self-perceived dyspnoea threshold during the 6MWT. This HR at the dyspnoea threshold is highly reproducible and enable estimation of the HR at the ventilatory threshold.

COPD recent findings: impact on clinical practice.

Chronic obstructive pulmonary disease is now considered as a systemic disease originating in the lungs. The natural history of this disease reveals numerous extrapulmonary manifestations and co-morbidity factors that complicate the evolution of COPD. Recent publications have documented these systemic manifestations and co-morbidities and clarified somewhat the role of muscle dysfunction, nutritional anomalies, endocrine dysfunction, anaemia, osteoporosis and cardiovascular and metabolic disorders as well as lung cancer and psychological elements in this complex disease. Importantly, recent studies have shown that effort intolerance, exertional desaturation, loss of autonomy and reduced physical activity, loss of muscle mass and quadriceps strength as well as dyspnoea and impaired quality of life can be considered as independent predictive factors for survival in COPD. Use of these data may advance understanding of mechanisms; improve evaluation and thereby patient management in COPD.

Contractile fatigue, muscle morphometry, and blood lactate in chronic obstructive pulmonary disease.

We hypothesized that patients with chronic obstructive pulmonary disease developing contractile fatigue of the quadriceps during cycle exercise may have characteristic metabolic and muscle features that could increase their susceptibility to fatigue, thus differentiating them from those who do not develop fatigue. We examined, in 32 patients, the fiber-type proportion, enzymatic activities, and capillary density in the vastus lateralis and the arterial blood lactate level during constant work-rate cycling exercise. Contractile fatigue was defined as a postexercise fall in quadriceps twitch force greater than 15% of resting values. Twenty-two patients developed contractile fatigue after exercise. No significant differences were found between fatiguers and non-fatiguers for the endurance time, fiber-type proportion, and oxidative enzyme activities. The lactate dehydrogenase activity was significantly higher (p < 0.05) and muscle capillarization significantly reduced in fatiguers (p < 0.05). Compared with non-fatiguers, the arterial lactate level during exercise was significantly higher in fatiguers (p < 0.001). A significant relationship was found between the fall in quadriceps twitch force and lactate dehydrogenase activity, capillary/fiber ratio, and blood lactate level. We conclude that changes in muscle enzymatic profile and capillarization with a greater reliance on glycolytic metabolism during exercise are associated with contractile fatigue in patients with chronic obstructive pulmonary disease.

Does oxidative stress alter quadriceps endurance in chronic obstructive pulmonary disease?

The role of exercise-induced oxidative stress in the reduced quadriceps endurance of chronic obstructive pulmonary disease (COPD) patients has never been shown. We conducted a randomized, double-blind, and crossover study in which nine severe patients performed localized dynamic quadriceps endurance tests at 40% of maximal strength after oral treatment with the antioxidant, N-acetylcysteine (NAC), and placebo. Venous blood was sampled before, immediately after exercise, and 6 hours later. Endurance time improved by 25% after NAC treatment compared with placebo (p < 0.05). Superoxide anion (oxidant) release by stimulated phagocytes decreased after 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 condition (p < 0.05) but not after treatment. Advanced oxidized protein products, another index of oxidative stress, were also increased 6 hours after exercise by 139 +/- 27% in the placebo condition but only by 54 +/- 19% after treatment (p < 0.05). This study shows that NAC treatment in COPD reduced basal disturbance in the prooxidant system, improved endurance time, and prevented exercise-induced oxidative stress. Oxidative stress thus seems to be implicated in the reduced quadriceps endurance of patients with COPD.

Exercise-induced quadriceps oxidative stress and peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease.

Exercise-induced muscle oxidative stress may be involved in the myopathy associated with chronic obstructive pulmonary disease (COPD). This study was designed to look at whether local exercise induces muscle oxidative stress and whether this oxidative stress may be associated with the reduced muscle endurance in patients with COPD. Quadriceps endurance was measured in 12 patients with COPD (FEV1 = 0.96 +/- 0.14 SEM) and 10 healthy sedentary subjects by repeated knee extensions of the dominant leg. Biopsies of the vastus lateralis muscle were obtained before and 48 hours after exercise. Muscle oxidative stress was measured by lipid peroxidation and oxidized proteins. Muscle antioxidant was evaluated by peroxidase glutathion activity. Quadriceps endurance was significantly reduced in patients with COPD when compared with the healthy control subjects (p < 0.01). Forty-eight hours postexercise, only patients with COPD had a significant increase in muscle lipid peroxidation (p < 0.05) and oxidized proteins (p < 0.05), whereas increased peroxidase glutathion activity was only observed in control subjects (p < 0.05). Both increases in muscle lipid peroxidation and oxidized proteins were significantly and inversely correlated with quadriceps endurance capacity in COPD (p < 0.05). In summary, local exercise induced muscle oxidative stress in patients with COPD, whereas it failed to raise antioxidant activity. In these individuals, muscle oxidative stress was associated with a reduced quadriceps endurance.