Exercise-Limiting Factors in Respiratory Distress

Abstract

Exercise performance data, circulatory function and respiratory and leg muscle quality, expressed as muscle fiber composition, are reviewed and together with our own data discussed as possible limiting factors for physical performance in chronic obstructive pulmonary disease (COPD). COPD is regarded as synonymous with reduced physical performance, exaggerated breathlessness or dyspnea, muscle hypo trophy and/or wasting and, frequently, malnutrition. Impaired right ventricular circulatory function seems to be essential. The observed preponderance of fast twitch (FT), ‘glycogenolytic’ and capillary-poor muscle fiber type in the investigated muscles might reflect endowment, a ‘hypoxic vaso-constriction’-related downregulation of the other main fiber type: the slow twitch (ST), capillary-rich, fatigue-resistant fiber, and/or selective muscle trauma to ST fibers. Ischemic heart disease (IHD) patients demonstrate a similar fiber type pattern in leg muscles. Both COPD and IHD patients have low leg muscle and plasma deposits of antioxidants such as coenzyme Q₁₀ (CoQ₁₀) and α-tocopherol. This could reflect a depressed resistance to radical induced cell trauma and/or malnutrition. The magnitude of the antioxidant reduction is less pronounced in patients rich in FT fibers indicating a ST fiber-related susceptibility to trauma. Treatment of other muscle disorders including heart muscle with, e.g., CoQ₁₀ improves performance due to a causative enhanced antioxidant potential, reduced catabolism and/or an upregulated muscle anabolism, increased mitochondrial volume/function, etc. Such data are lacking in COPD.

Skeletal muscle dysfunction in chronic obstructive pulmonary disease and chronic heart failure: underlying mechanisms and therapy perspectives

“…A IIb/x→I shift was also observed when the distribution of MyHC isoforms was analyzed in diaphragms of patients with CHF (70) or COPD (71). Furthermore, a larger population of type I fibers in the diaphragm (corrected for the percentage of type I fibers in the quadriceps femoris) was found in both COPD and CHF patients (26,72) compared with sedentary control subjects (68,73). The proportion of type I fibers in both the internal and external inter-costal muscles was Ϸ62% in both COPD patients and control subjects in some studies (68,74), but in other studies COPD patients had lower proportions of type I fibers (46-48%) in these muscles (73,75).…”

“…In healthy subjects as well as in patients with COPD or CHF, exercise-limiting symptoms are the sense of leg effort (exertional discomfort) or breathlessness (exertional dyspnea) (23,24). Thus, despite correlations between peripheral muscle strength and performance in COPD and CHF (18,23,25), reduced endurance (ie, fatigue) seems to be the dominant limiting factor in peripheral muscles in these patients because the sense of leg effort was one of the main reasons to stop exercising (4,24,(26)(27)(28)(29). It was shown that early lactic acidosis occurs in COPD during exercise (30,31) and that this is largely the result of lactate release from the lower exercising limbs (32).…”

Lactate Kinetics during Exercise in Chronic Obstructive Pulmonary Disease

“…Using serial lactate concentration measurements during exercise, previous studies have shown that the lactate kinetics are abnormal in COPD patients; for a given submaximal exercise level, the concentration of blood lactate is greater in patients than in normal subjects (2,8,10,11). However, the prevalence of this phenomenon is difficult to evaluate, and it is commonly believed that, because of ventilatory limitation, the vast majority of patients with COPD are unable to exercise sufficiently to activate their skeletal muscles and, thereby, produce a significant amount of lactic acid (12,13).…”