Impaired skeletal muscle endurance related to physical inactivity and altered lung function in COPD patients

Evaluation of oxygen uptake kinetics and oxygen kinetics of peripheral skeletal muscle during recovery from exercise in patients with chronic obstructive pulmonary disease

The biochemical features of skeletal muscle and its contribution to exercise intolerance in patients with chronic obstructive pulmonary disease (COPD) is under active investigation. Near-infrared spectroscopy (NIRS) can non-invasively provide information on the oxidative capacity of muscle. To clarify whether oxygenation of peripheral muscle is one determinant of exercise tolerance, we simultaneously examined the oxygen uptake (V O 2off) kinetics and oxygen kinetics of peripheral skeletal muscle evaluated by NIRS during recovery from exercise in COPD patients. Fifteen patients with COPD and five normal control subjects performed a symptom-limited incremental exercise test. On the following day, all patients performed a constant work rate exercise test while being monitored using NIRS continuously for changes in concentration of oxygenated haemoglobin (HbO2) and during expired gas analysis. We found that the time constant of during recovery from constant work rate exercise (V O 2off) and the time constant of V O 2off during recovery (tau V O 2off) were significantly longer in COPD patients than in normal control subjects. was inversely correlated with absolute values of forced expiratory volume in 1 s (FEV1.0) and FEV1.0 (% predicted). However, no significant correlation was found between and FVC (forced vital capacity), FEV1.0/FVC, or diffusing capacity of the lung for CO (DLCO). Moreover, was inversely correlated with maximal V O 2off and maximal work rate. In contrast, exhibited a significant positive correlation with tau V O 2off. These results indicate that V O 2off kinetics during recovery is related to re-oxygenation of peripheral skeletal muscle evaluated by NIRS in patients with COPD. Therefore, NIRS may be a useful tool to estimate the impairment of cardiopulmonary responses and re-oxygenation of peripheral skeletal muscle during the immediate recovery phase after exercise in COPD patients.

Contractile leg fatigue after cycle exercise: a factor limiting exercise in patients with chronic obstructive pulmonary disease

We evaluated whether contractile fatigue of the quadriceps occurs after cycling exercise in patients with chronic obstructive pulmonary disease (COPD) and whether it could contribute to exercise limitation. Eighteen COPD patients performed two constant work-rate cycling exercises up to exhaustion. These tests were preceded by nebulization of placebo or 500 microg of ipratropium bromide. Muscle fatigue was defined as a postexercise reduction in quadriceps twitch force of more than 15% of the resting value. There was an increase in endurance time postipratropium compared with placebo nebulization (440 +/- 244 seconds vs. 322 +/- 188 seconds, p = 0.06). Nine patients developed contractile fatigue after placebo exercise. In these patients, ipratropium did not increase the endurance time (394 +/- 220 seconds with placebo vs. 400 +/- 119 seconds with ipratropium) despite an 11% improvement in FEV1. In the nine patients who did not fatigue after placebo exercise, endurance time increased from 249 +/- 124 seconds with placebo to 479 +/- 298 seconds with ipratropium (p < 0.05). There was a significant correlation between the improvement in endurance time with ipratropium and quadriceps twitch force at 10 minutes after placebo exercise (r = 0.59, p = 0.01). The occurrence of contractile fatigue during exercise may explain why bronchodilation fails to improve exercise tolerance in some COPD patients.

ROS in the local and systemic pathogenesis of COPD

An imbalance between oxidants and antioxidants is proposed in the pathogenesis of COPD. Potential alterations responsible for an imbalance in oxidant production and intra- and extracellular antioxidant defense systems are discussed with respect to COPD-related changes in the pulmonary compartment. In line with the current view of COPD as a disease with multiple systemic consequences, there is increasing evidence that imbalances in the redox milieu extend beyond the diseased lung in COPD patients. Skeletal muscle dysfunction is often observed in COPD and may result from imbalances in the redox environment of skeletal muscle. Potential triggers of oxidative stress in the muscle compartment include inflammation and hypoxia, and local sources of reactive oxygen and nitrogen species are discussed, as well the mechanisms by which skeletal muscle trophical state, contractility and fatigability may be affected by oxidative stress, resulting in skeletal muscle dysfunction.

Quadriceps fatigability after single muscle exercise in patients with chronic obstructive pulmonary disease

The purpose of this study was to compare quadriceps fatigability in patients with varying severity of chronic obstructive pulmonary disease with age-matched control subjects. Ten healthy control subjects, 8 patients with severe disease (FEV1 less than 35% predicted), and 11 patients with mild to moderate disease were studied. The FEV1 was 1.75 +/- 0.13 L (SE), 50.4 +/- 2.9% of predicted in the mild to moderate group, and 0.87 +/- 0.06 L, 25.9 +/- 1.9% of predicted in the severe group. Quadriceps fatigue was quantified by the reduction in potentiated twitch force after a potentially fatiguing task. All subjects performed three sets of 10 maximum voluntary contractions of the right quadriceps muscle. Quadriceps maximum voluntary contraction force was 58.3 +/- 3.3 kg for the healthy older group, 49.0 +/- 4.2 kg in the mild to moderate group, and 44.3 +/- 4.7 kg in the severe group. The fall in potentiated twitch force after exercise was significantly greater in the patients with severe disease than in the healthy control subjects. In conclusion, the quadriceps in patients with severe chronic obstructive pulmonary disease are more fatigable than those in age- and sex-matched healthy control subjects.

Muscle strength and exercise kinetics in COPD patients with a normal fat-free mass index are comparable to control subjects

STUDY OBJECTIVE

This study was designed to investigate the extent of clinical muscle dysfunction in stable patients with COPD who were attending an out-patient pulmonary clinic compared with that of age-matched control subjects without COPD.

DESIGN AND SUBJECTS

Respiratory muscle and hand grip strength, steady-state O(2) kinetics, and body composition were measured in 32 patients with COPD (19 women) [mean (+/- SD) FEV(1), 38 +/- 11% predicted] and 36 age-matched control subjects (13 women).

RESULTS

Measurements of handgrip force (mean, 97 +/- 32% vs 106 +/- 26% predicted, respectively), maximal expiratory pressure (mean, 57 +/- 33% vs 61 +/- 22% predicted, respectively), steady-state O(2) kinetics (mean tau, 72 +/- 34 s vs 78 +/- 37 s, respectively) and steady-state CO(2) kinetics (mean tau, 77 +/- 38 s vs 65 +/- 32 s, respectively) at submaximal exercise were similar in patients and control subjects. All the subjects, except for one female COPD patient, had a normal fat-free mass index (FFMI), although on average the FFMI was lower in male patients (19.8 +/- 2.8) than in male control subjects (23.0 +/- 2.8; p < 0.01).

CONCLUSIONS

In patients with COPD who were attending a regular outpatient pulmonary clinic, there was no evidence of reduced upper extremity and expiratory muscle strength or prolonged O(2) and CO(2) kinetics during isowork submaximal cardiopulmonary exercise compared to healthy, age-matched control subjects. Also, a normal body composition was found in nearly all COPD patients. This argues against the existence of a clinically significant systemic myopathy in most stable patients with severe COPD and normal FFMI.

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.

Quadriceps fatigue after cycle exercise in patients with COPD compared with healthy control subjects

STUDY OBJECTIVES

Quadriceps fatigue can occur in patients with COPD after exhaustive cycle exercise. The purpose of this study was to determine whether the degree of fatigue elicited by cycle exercise was greater in patients with COPD compared with matched control subjects.

SUBJECTS

Nine male patients with COPD with a mean (+/- SE) age of 66 +/- 3 years and mean FEV(1) values of 1.31 +/- 0.15 L and 36 +/- 5% predicted were compared to nine healthy male subjects with a mean age of 66 +/- 2 years.

METHODS

Patients with COPD exercised at 60% of peak work capacity until exhaustion. Healthy elderly subjects exercised at a workload that was chosen to produce a similar absolute oxygen uptake (O(2)) during constant-load exercise as that obtained by the patients with COPD. Quadriceps fatigue was detected by measuring twitch force (unpotentiated twitch force [TwQu] and potentiated twitch force [TwQp]) before and after cycle exercise.

RESULTS

Patients with COPD exercised for a mean duration of 8.4 +/- 1.8 min. O(2) during exercise was 50 +/- 6% of predicted. The healthy elderly control subjects exercised for 10 min, generating a O(2) of 48 +/- 1% predicted. TwQu fell significantly postexercise in the patients with COPD but not in the matched control subjects. TwQp fell significantly postexercise in both groups, but the fall in TwQp postexercise was significantly greater in the patients with COPD.

CONCLUSION

For the same absolute O(2) and duration of cycle exercise, the amount of fatigue elicited was significantly greater in the patients with COPD compared to age-matched healthy control subjects.

Dual morphometrical changes of the deltoid muscle in patients with COPD

The present study was specifically aimed at evaluating if the structure of the deltoid muscles is modified in patients with chronic obstructive pulmonary disease (COPD). Twenty-eight male volunteers (61+/-13 yr) were assigned, according to pulmonary function, to either the COPD (n=14, FEV(1)=22-74%pred) or control group (n=14, FEV(1)=83-121%pred). Biopsies from non-dominant deltoid muscle were obtained and processed for morphometric analysis of the fibre types. Both type I and type II muscle fibres were distributed in the typical mosaic pattern. The mean value of the fibre size was within the normal range. However, three differentiated modes were observed in the deltoid from COPD patients: a central mode of normal sized fibres, a mode of atrophic fibres and a mode of hypertrophic fibres. This observation was evident even within single fascicles and especially prevalent in the most severe COPD patients. We conclude that factors with opposite effect (promotion of either atrophy or hypertrophy) exert relevant roles in the histomorphometrical characteristics of the deltoid muscles in COPD patients.

Electrophysiologic changes during exercise testing in patients with chronic obstructive pulmonary disease

To determine whether skeletal muscle is involved in the exercise limitation of chronic obstructive pulmonary disease (COPD), we investigated electrical adaptations in muscle during incremental cycling exercise testing. Changes in quadriceps activity were compared using surface electromyography (SEMG) and motor point stimulation in ten COPD patients and ten healthy subjects. Patients showed significantly lower exercise capacity, and M-wave duration was increased from exercise onset (P < 0.05) with a parallel decrease in amplitude (P < 0.05). The SEMG power spectrum median frequency was always higher (P < 0.04) in patients and its decline was earlier (P < 0.01). The ratio of the root mean square of the SEMG to oxygen uptake was decreased (P < 0.001) during exercise in patients, although it remained constant in controls. Electromyographic parameters were significantly more involved in the exercise limitation than ventilatory factors. Thus, modified electrical activity in muscle appeared in COPD patients from exercise onset, indicating that skeletal muscle function is clearly implicated in the exercise intolerance of these patients.

A randomized, controlled trial comparing long-term and short-term exercise in patients with chronic obstructive pulmonary disease

PURPOSE

To compare the effects of short-term (3 months) and long-term (18 months) involvement in an exercise program on self-reported disability and physical function in patients with chronic obstructive pulmonary disease (COPD).

METHODS

A total of 140 patients with COPD were studied in a randomized, single-blinded clinical trial. Self-reported disability and physical function were assessed using a 21-item questionnaire, a 6-minute walk, timed stair climb, and an overhead task.

RESULTS

At the completion of the trial, participants in the long-term intervention reported 12% less disability than those in the short-term intervention (adjusted mean with 95% confidence interval, 1.53 (1.43-1.63) versus 1.71 (1.61 to 1.81) units, respectively; P=.016), walked 6% farther during 6-minutes (1,815.0 [1,750.4-1,879.6] vs 1,711.5 [1,640.7-1,782.3] feet, respectively), climbed steps 11% faster (11.6 [11.0-12.2] vs 12.9 [12.3-13.5] seconds, respectively), and completed an overhead task 8% faster (46.8 [44.4-49.2] vs 50.4 [47.8-53.0] seconds, respectively) than those in the short-term intervention.

CONCLUSION

An 18 month exercise program results in greater improvements in self-reported disability and physical function in patients with COPD when compared with a 3-month exercise program. As such, long-term exercise should be recommended for all patients with COPD.

Cerebral oxygenation during exercise in patients with terminal lung disease

STUDY OBJECTIVES

In patients with terminal lung disease who were exercising, we assessed whether improved arterial O2 saturation with an increased fraction of inspired oxygen (FIO2) affects cerebral oxygenation.

DESIGN

Randomized, crossover.

PATIENTS AND METHODS

The cerebral changes in oxyhemoglobin (DeltaHbO2) and changes in deoxyhemoglobin (DeltaHb) levels were evaluated using near-infrared spectrophotometry and the middle cerebral artery (MCA) mean velocity (V(mean)) was determined by transcranial Doppler ultrasonography in 13 patients with terminal lung disease (New York Heart Association class III-IV). Patients were allocated to an FIO2 of either 0.21 or 0.35 during incremental exercise with 15 min between trials.

RESULTS

Peak exercise intensity (mean [+/- SE], 26 +/- 4 W) reduced the arterial O2 pressure (at rest, 64 +/- 3 mm Hg; during exercise, 56 +/- 3 mm Hg) and the arterial oxygen saturation (SaO2) [at rest, 92 +/- 2%; 87 +/- 2%; p < 0.05], while the arterial CO2 pressure was not significantly affected. The MCA V(mean) increased from 49 +/- 5 to 63 +/- 7 cm/s (p < 0.05) as did the DeltaHb, while the DeltaHbO2 remained unaffected by exercise. With an elevated FIO2, the SaO2 level (at rest, 95.8 +/- 0.7%; during exercise, 96.0 +/- 1.0%) and arterial O2 pressure (at rest, 102 +/- 11 mm Hg; during exercise, 100 +/- 8 mm Hg) were not significantly affected by exercise, and the levels of blood oxygenation remained higher than the values established at normoxia (p < 0.05). The MCA V(mean) increased to a level similar to that achieved during control exercise (ie, to 70 +/- 11 cm/s). In contrast to control exercise, DeltaHb decreased while DeltaHbO2 increased during exercise with 35% O2 (p < 0.05).

CONCLUSION

An O2-enriched atmosphere enabled patients with terminal lung disease to maintain arterial O2 saturation during exercise. An exercise-induced increase in cerebral perfusion was not affected by hyperoxia, whereby the enhanced availability of oxygenated hemoglobin increases cerebral oxygenation. The clinical implication of the study is that during physical activity patients with terminal lung disease are recommended to use an elevated FIO2 to protect cerebral oxygenation.

Isokinetic muscle function in COPD

AIM

Exercise limitation in patients with COPD has been attributed to impaired ventilation and reduced skeletal muscle function. We have previously used a combination of FEV(1) and leg muscle function (work achieved during a 30-s isokinetic sprint test) to predict progressive exercise capacity. However, the 30-s test may not be well tolerated in patients with advanced lung disease. We studied the relationship between progressive exercise capacity, FEV(1), and isokinetic work in patients with COPD and in healthy control subjects to assess whether the work accomplished at time intervals of < 30 s could also be used to predict progressive maximal exercise capacity (Wmax).

METHODS

Twenty-seven patients with COPD and 29 control subjects underwent anthropometric measures, spirometry, progressive cycle ergometry, and 30-s isokinetic cycling.

RESULTS

There was no significant difference for weight, height, or body mass index between the groups. The COPD group was slightly older and had a significantly lower FEV(1) than control subjects. They also had a lower Wmax (56 +/- 28.3 W vs 141.9 +/- 46.7 W) and isokinetic work accomplished over 10 s (W10), over 15 s (W15), over 20 s (W20), over 25 s (W25), and over 30 s (W30). Wmax correlated in both patients with COPD and in control subjects with W10, W15, W20, W25, W30, and FEV(1). Combining FEV(1) and isokinetic work (W10, W15, W20, W25, or W30) in a two-factor model to predict Wmax, the coefficients of determination (r(2)) for patients with COPD were 0.57, 0.57, 0.58, 0.59, and 0.58, and for control subjects were 0.69, 0.69, 0.71, 0.71, and 0.73, respectively. Wmax correlated with weight only in control subjects.

CONCLUSIONS

Both ventilatory function and leg muscle function contribute to exercise limitation, and a 20-s isokinetic test can be utilized to assess leg function in patients with COPD.

The contribution of starvation, deconditioning and ageing to the observed alterations in peripheral skeletal muscle in chronic organ diseases

Muscle weakness and early fatigue are common symptoms of chronic organ diseases, like chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF) and chronic renal failure (CRF). It is becoming more and more clear that symptom intensities and exercise intolerance are related to muscle wasting and intrinsic alterations in peripheral skeletal muscle in these patient populations, while correlations with parameters of organ functioning are poor. Also, changes in muscle structure and function in COPD, CHF and CRF show much resemblance. Semi-starvation, reduced physical activity and ageing are external factors possibly confounding a direct relationship between the primary organ impairments and alterations in peripheral skeletal muscle and exercise capacity. Reducing the catabolic effects of the various contributing factors might improve muscle function and health status in chronic disease. In this review, we present a systematic overview of human studies on alterations in skeletal muscle function, morphology and energy metabolism in COPD, CHF, CRF and we compare the results with comparable studies in anorexia nervosa, disuse or inactivity and ageing. Unravelling the relative contributions of these external factors to the observed alterations in the various diseases may contribute to targeted intervention strategies to improve muscle function in selected groups of patients.

Skeletal muscle dysfunction in chronic obstructive pulmonary disease

It has become increasingly recognized that skeletal muscle dysfunction is common in patients with chronic obstructive pulmonary disease (COPD). Muscle strength and endurance are decreased, whereas muscle fatigability is increased. There is a reduced proportion of type I fibers and an increase in type II fibers. Muscle atrophy occurs with a reduction in fiber cross-sectional area. Oxidative enzyme activity is decreased, and measurement of muscle bioenergetics during exercise reveals a reduced aerobic capacity. Deconditioning is probably very important mechanistically. Other mechanisms that may be of varying importance in individual patients include chronic hypercapnia and/or hypoxia, nutritional depletion, steroid usage, and oxidative stress. Potential therapies include exercise training, oxygen supplementation, nutritional repletion, and administration of anabolic hormones.

Metabolic characteristics of the deltoid muscle in patients with chronic obstructive pulmonary disease

The purpose of this study was to analyse key enzyme activities of the deltoid muscle (DM) in chronic obstructive pulmonary disease (COPD) patients. The activities of one oxidative enzyme (citrate synthase (CS)), two glycolytic enzymes (lacatate dehydrogenase (LD); and phosphofructokinase (PFK)) and one enzyme related to the use of energy stores (creatine kinase (CK)) were determined in the DM of 10 patients with COPD and nine controls. Exercise capacity (cycloergometry) and the handgrip strength were also evaluated. Although exercise capacity was markedly reduced in COPD (57 +/- 20% predicted), their handgrip strength was relatively preserved (77 +/- 19% pred). The activity of LD was higher in the COPD patients (263.9 +/- 68.2 versus 184.4 +/- 46.5 mmol x min(-1) x g(-1), p<0.01), with a similar trend for CS (67.3 +/- 33.3 versus 46.0 +/- 17.4 mmol x min(-1) x g(-1), p = 0.07). Interestingly, the activity of the latter enzyme was significantly higher than controls if only severe COPD patients were considered (81.8 +/- 31.2 mmol x min(-1) x g(-1), p < 0.01). PFK and CK activities were similar for controls and COPD. Chronic obstructive patients show a preserved or even increased (severe disease) oxidative capacity in their deltoid muscle. This coexists with a greater capacity in the anaerobic part of the glycolysis. These findings are different to those previously observed in muscles of the lower limbs.

Insulin resistance and associated metabolic abnormalities in muscle: effects of exercise

Skeletal muscle is a major site of insulin resistance. In addition to glucose transport, oxidative disposal and storage defects, insulin resistant muscle exhibit many other metabolic abnormalities. After a brief review of insulin resistance determinants, we will focus on muscular abnormalities in obesity and type 2 diabetes. Glucose and lipid metabolism defects will be analysed and their interactions discussed. Exercise can improve many of these muscular abnormalities and the mechanisms underlying exercise-induced benefits have been clarified during the past decades. Therefore, exercise training has proved to be useful in the management of insulin resistant states, i.e. mainly obesity, especially in its truncal distribution, and type 2 diabetes. However, exercise prescription remains poorly codified, and results on glycaemic control are sometimes conflicting. In the last part of this review, we will emphasize the pathophysiological basis for an individualized exercise prescription in insulin resistant subjects.

Peripheral muscle dysfunction in chronic obstructive pulmonary disease

Peripheral muscle dysfunction is a common systemic complication of moderate to severe COPD and may contribute to disability, handicap, and premature mortality. In contrast to the lung impairment, which is largely irreversible, peripheral muscle dysfunction is potentially remediable with exercise training, nutritional intervention, oxygen, and anabolic drugs. Therapeutic success is often incomplete, however, and a better understanding of the mechanisms involved in the development of peripheral muscle dysfunction in COPD is needed to help develop innovative and more effective therapeutic strategies.

Exercise training in chronic obstructive pulmonary disease

Exercise limitation is a common and disturbing manifestation of COPD. The exercise intolerance is often caused by multiple interrelated anatomic and physiologic disturbances. Importantly, exercise tolerance can be improved despite the presence of fixed structural abnormalities in the lung. Exercise training, undertaken alone or in the context of comprehensive PR, improves exercise endurance and, to a lesser degree, the maximal tolerated workload of patients with COPD. Pulmonary rehabilitation also improves dyspnea and QOL. Exercise training and PR should be considered for all patients lacking contraindications who experience exercise intolerance despite optimal medical therapy. Lower-extremity training should be included routinely in the exercise prescription. The choice of type and intensity of training should be based primarily on the patient's individual baseline functional status, symptoms, needs, and long-term goals. When tolerated, high-intensity (continuous or interval) training may lead to greater improvements in aerobic fitness than low-intensity training but is not absolutely necessary to achieve gains in exercise endurance. Upper-extremity training should be undertaken when possible. Ventilatory muscle training should be considered for patients who continue to experience exercise limitation and breathlessness despite medical therapy and general exercise reconditioning. Exercise tolerance may improve following exercise training because of gains in aerobic fitness or peripheral muscle strength; enhanced mechanical skill and efficiency of exercise; improvements in respiratory muscle function, breathing pattern, or lung hyperinflation; as well as reduction in anxiety, fear, and dyspnea associated with exercise. Gains made in exercise tolerance can last up to 2 years following a limited duration (6-12 week) rehabilitation program.

Distribution of muscle weakness in patients with stable chronic obstructive pulmonary disease

PURPOSE

The authors determined the degree of respiratory and peripheral muscle weakness in patients with moderate to severe chronic obstructive pulmonary disease (COPD). Differences in severity of muscle weakness among muscle groups may provide treatment options, such as selective muscle training, to adapt the exercise prescription in pulmonary rehabilitation programs. In addition, this information may add to the knowledge on the mechanisms of muscle weakness.

METHODS

Respiratory and peripheral muscle force were quantified in 22 healthy elderly subjects and 40 consecutive COPD patients (forced expiratory volume in 1 second, percent of predicted value [% pred] 41 +/- 19; transfer factor for carbon monoxide, % pred 47 +/- 26) admitted to a pulmonary rehabilitation program. Lung function, diffusing capacity, isometric force of four peripheral muscle groups (handgrip, elbow flexion, shoulder abduction, and knee extension), neck flexion force, and maximal inspiratory and expiratory pressures were measured.

RESULTS

Patients had reduced respiratory muscle strength (mean 64% of control subjects' value [% control]) and peripheral muscle strength (mean 75% control) compared to normal subjects. Inspiratory muscle strength (59 +/- 18% control) was significantly lower than expiratory muscle strength (69 +/- 25% control) and peripheral muscle strength (P < 0.01). Neck flexion force (80 +/- 19% control) was better preserved than maximal inspiratory pressure and shoulder abduction force (70 +/- 15% control, P < 0.01). Handgrip force (78 +/- 16% control) and elbow flexion force (78 +/- 14% control) were significantly less affected than shoulder abduction force (70 +/- 15% control, P < 0.01). Finally, shoulder abduction force and knee-extension force (72 +/- 24% control) were not significantly different.

CONCLUSIONS

Muscle weakness in stable COPD patients does not affect all muscles to a similar extent. Inspiratory muscle force is affected more than peripheral muscle force, whereas proximal upper limb muscle strength was impaired more than distal upper limb muscle strength.

Quadriceps fatigue after cycle exercise in patients with chronic obstructive pulmonary disease

Patients with COPD have derangements in respiratory mechanics that may cause them to stop exercising before the exercising limb muscles reach their functional limits. However, because lung disease makes activity unpleasant, patients with chronic obstructive pulmonary disease (COPD) often adapt a sedentary lifestyle leading to progressive deconditioning. Deconditioning will lead to progressive deterioration in limb muscle function, which could adversely affect exercise capacity. The purpose of this study was to determine whether fatigue of the quadriceps muscle occurs after high intensity cycle exercise to the limits of tolerance in patients with moderate to severe COPD. Nineteen male patients with COPD (FEV(1) 1.54 +/- 0. 12 L; 42 +/- 3% predicted) exercised at 60 to 70% of their predetermined maximal work capacity until exhaustion. The femoral nerve was supramaximally stimulated with a figure-of-eight magnetic coil, and quadriceps twitch force (TwQ) was measured before and at 10, 30, and 60 min postexercise. Patients exercised at 53.7 +/- 4.1 watts for 10.4 +/- 1.4 min. Peak V O(2) was 1.24 +/- 0.08 L/min (51. 3 +/- 3.6% predicted). TwQ fell significantly postexercise; 79.2 +/- 5.4% of baseline value at 10 min postexercise (p < 0.005), 75.7 +/- 4.8% at 30 min postexercise (p < 0.001), and 84.0 +/- 5.0% at 60 min postexercise (p < 0.005). Acceptable M-waves from the quadriceps muscle (not obscured by stimulus artifact) were obtained in six subjects. M-wave amplitude was unchanged from baseline at all times postexercise indicating that the fall in TwQ was due to contractile fatigue and not to transmission failure. In conclusion, contractile fatigue of the quadriceps muscle occurs after high intensity cycle exercise to the limits of tolerance in patients with COPD.

Skeletal muscle abnormalities in patients with COPD: contribution to exercise intolerance

Exercise intolerance in COPD patients appears to be in part because of skeletal muscle dysfunction. Studies using biopsy techniques and magnetic resonance spectroscopy have demonstrated changes in enzyme activities and metabolism that indicate reduced oxidative capacity in the peripheral muscles of these patients. Regarding the respiratory muscles, the biochemical characteristics have been studied in only a few works and the results seem to depend on the specific muscle group studied. Several factors, such as hypoxemia, nutritional status, pharmacological treatment, and deconditioning, may be responsible for these skeletal muscle abnormalities. This brief review describes the changes in peripheral and respiratory muscles in COPD patients based on data from the literature. The causes of these muscle abnormalities, their contribution to exercise intolerance, and the effects of training are then discussed. We conclude with suggested directions for future investigation using contemporary noninvasive technologies.