Exercise capacity and ventilatory, circulatory, and symptom limitation in patients with chronic airflow limitation

Pain in people with chronic obstructive pulmonary disease (COPD)

INTRODUCTION

The prevalence and characteristics of pain are not known in COPD patients. The purposes of this study were to determine if pain is more common in COPD patients than in healthy people and if it was related to self-reported physical activity, health related quality of life (HRQoL) and comorbidities.

METHODS

Participants returned a mailed survey package that contained: 1) McGill Pain Questionnaire (MPQ) and Brief Pain Inventory (BPI) to evaluate pain severity and how pain interferes with activities; 2) Tampa Scale for Kinesiophobia (TSK) to evaluate fear of movement related to pain; 3) Short Form-36 (SF-36), to measure HRQoL; 4) Community Health Activities Model Program for Seniors (CHAMPS) to evaluate physical activity; 5) a form to list medications and comorbidities.

RESULTS

Forty-seven COPD patients and 47 age- and gender-matched healthy people responded. People with COPD demonstrated more pain (MPQ and BPI, p = 0.000), a greater pain-related interference in their lives (BPI, p = 0.000), a higher pain-related fear of movement, and lower frequency and energy expenditure of physical activities (CHAMPS, p = 0.000) than healthy people (TSK, p < 0.001). Pain severity (MPQ and BPI) was indirectly correlated to the Physical Component Score of the SF-36. COPD patients identified pain in the neck and trunk 3.1 times more often than healthy people. The number of comorbidities was the most consistent independent correlate of pain in COPD patients.

CONCLUSIONS

COPD patients demonstrate more pain which interferes with activities more so than healthy people of similar age. Pain is also negatively associated with HRQoL in COPD.

Mechanisms of non-pharmacologic adjunct therapies used during exercise in COPD

Individuals with chronic obstructive pulmonary disease (COPD) are often limited in their ability to perform exercise due to a heightened sense of dyspnea and/or the occurrence of leg fatigue associated with a reduced ventilatory capacity and peripheral skeletal muscle dysfunction, respectively. Pulmonary rehabilitation programs have been shown to improve exercise tolerance and health related quality of life. Additional therapeutic approaches such as non-invasive ventilatory support (NIVS), heliox (He-O(2)) and supplemental oxygen have been used as non-pharmacologic adjuncts to exercise to enhance the ability of patients with COPD to exercise at a higher exercise-intensity and thus improve the physiological benefits of exercise. The purpose of the current review is to examine the pathophysiology of exercise limitation in COPD and to explore the physiological mechanisms underlying the effect of the adjunct therapies on exercise in patients with COPD. This review indicates that strategies that aim to unload the respiratory muscles and enhance oxygen saturation during exercise alleviate exercise limiting factors and improve exercise performance in patients with COPD. However, available data shows significant variability in the effectiveness across patients. Further research is needed to identify the most appropriate candidates for these forms of therapies.

Impaired adrenergic- and corticotropic-axis outflow during exercise in chronic obstructive pulmonary disease

Exercise stimulates coordinated release of the sympathoadrenal hormones adrenocorticotropic hormone (ACTH), cortisol, norepinephrine (NE), and epinephrine (Epi). The study hypothesis was that chronic obstructive pulmonary disease (COPD) is marked by heightened sympathoadrenal outflow at comparable relative workloads. The location of the study was at a clinical research unit. Eight healthy men and 9 men with stable COPD (forced expiratory volume at 1 second <75% predicted) were studied. Volunteers rested (baseline) or exercised at individual submaximal (35% ± 5%) or maximal oxygen consumption. Blood was sampled every 2 minutes for 40 minutes concurrently. Two-way analysis of covariance was applied to examine group (healthy/COPD) and exercise (3 levels) effects on ACTH, cortisol, NE, and Epi release and regularity (estimable by approximate entropy). The timing of peak hormone concentrations was Epi, 14 minutes; NE, 16 minutes; ACTH, 22 minutes; and cortisol, 34 minutes in both cohorts. Type of exercise regimen influenced all 4 hormones (each P < .001), and subject group (control vs COPD) affected cortisol (P < .001) and Epi (P = .048) responses. Exercise regimen and group together controlled ACTH, cortisol, and Epi (each P < .001), but not NE, responses. In particular, endocrine responses were attenuated in COPD compared with control subjects. Approximate entropy analysis also identified loss of maximal exercise-induced ACTH-secretory regularity in COPD patients (P = .042). These outcomes demonstrate impaired rather than augmented exercise-associated sympathocorticotropic-axis outflow in patients with COPD even when outcomes are normalized to maximal oxygen consumption, suggesting that factors other than fitness are at work.

Sex differences in exertional dyspnea in patients with mild COPD: physiological mechanisms

The purpose of this study was to evaluate the physiological basis for sex-differences in exercise-induced dyspnea in patients with mild COPD. We compared operating lung volumes, breathing pattern and dyspnea during incremental cycling in 32 men (FEV(1)=86±10% predicted) and women (FEV(1)=86±12% predicted) with mild COPD and 32 age-matched controls. There were no sex differences in dyspnea in the control group at any work-rate or ventilation (V(E)). Women with COPD had significantly greater dyspnea than men at 60 and 80 W. At 80 W, dyspnea ratings were 5.7±2.3 and 3.3±2.5 Borg units (P<0.05) and the V(E) to maximal ventilatory capacity ratio was 72% and 55% in women and men, respectively (P<0.05). Comparable increases in dynamic hyperinflation were seen in both male and female COPD groups at symptom limitation but women reached tidal volume constraints at a lower work rate and V(E) than men. Superimposing mild COPD on the normal aging effects had greater sensory consequences in women because of their naturally reduced ventilatory reserve.

Cardiopulmonary exercise testing: relevant but underused

Cardiopulmonary exercise testing (CPX) is a relatively old technology, but has sustained relevance for many primary care clinical scenarios in which it is, ironically, rarely considered. Advancing computer technology has made CPX easier to administer and interpret at a time when our aging population is more prone to comorbidities and higher prevalence of nonspecific symptoms of exercise intolerance and dyspnea, for which CPX is particularly useful diagnostically and prognostically. These discrepancies in application are compounded by patterns in which CPX is often administered and interpreted by cardiology, pulmonary, or exercise specialists who limit their assessments to the priorities of their own discipline, thereby missing opportunities to distinguish symptom origins. When used properly, CPX enables the physician to assess fitness and uncover cardiopulmonary issues at earlier phases of work-up, which would therefore be especially useful for primary care physicians. In this article, we provide an overview of CPX principles and testing logistics, as well as some of the clinical contexts in which it can enhance patient care.

Evidence that a higher ATP cost of muscular contraction contributes to the lower mechanical efficiency associated with COPD: preliminary findings

Impaired metabolism in peripheral skeletal muscles potentially contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). We used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to examine the energy cost and skeletal muscle energetics in six patients with COPD during dynamic plantar flexion exercise compared with six well-matched healthy control subjects. Patients with COPD displayed a higher energy cost of muscle contraction compared with the controls (control: 6.1 ± 3.1% of rest·min(-1)·W(-1), COPD: 13.6 ± 8.3% of rest·min(-1)·W(-1), P = 0.01). Although, the initial phosphocreatine resynthesis rate was also significantly attenuated in patients with COPD compared with controls (control: 74 ± 17% of rest/min, COPD: 52 ± 13% of rest/min, P = 0.04), when scaled to power output, oxidative ATP synthesis was similar between groups (6.5 ± 2.3% of rest·min(-1)·W(-1) in control and 7.8 ± 3.9% of rest·min(-1)·W(-1) in COPD, P = 0.52). Therefore, our results reveal, for the first time that in a small subset of patients with COPD a higher ATP cost of muscle contraction may substantially contribute to the lower mechanical efficiency previously reported in this population. In addition, it appears that some patients with COPD have preserved mitochondrial function and normal energy supply in lower limb skeletal muscle.

Altered mitochondrial regulation in quadriceps muscles of patients with COPD

Evidence exists for locomotor muscle impairment in patients with chronic obstructive pulmonary disease (COPD), including fiber type alterations and reduced mitochondrial oxidative capacity. In this study high-resolution respirometry was used to quantify oxygen flux in permeabilized fibres from biopsies of the vastus lateralis muscle in patients with COPD and compared to healthy control subjects. The main findings of this study were that (i) routine state 2 respiration was higher in COPD; (ii) state 3 respiration in the presence of ADP was similar in both groups with substrate supply of electrons to complex I (COPD 38·28 ± 3·58 versus control 42·85 ± 3·10 pmol s(-1) mg tissue(-1) ), but O(2) flux with addition of succinate was lower in COPD patients (COPD 63·72 ± 6·33 versus control 95·73 ± 6·53 pmol s(-1) mg tissue(-1) ); (iii) excess capacity of cytochrome c oxidase in COPD patients was only ~50% that of control subjects. These results indicate that quadriceps muscle mitochondrial function is altered in patients with COPD. The regulatory mechanisms underlying these functional abnormalities remain to be uncovered.

Changes in six-minute walking distance during pulmonary rehabilitation in patients with COPD and in healthy subjects

Background:

The six-minute walking distance (6MWD) test has demonstrated validity and reliability to assess changes in functional capacity following pulmonary rehabilitation in patients with chronic obstructive lung disease. However, no attempt has been made to establish an iterative measurement of 6MWD during the overall period of pulmonary rehabilitation. Therefore, the aim of this study was to evaluate the impact of a twelve-week rehabilitation program on the iterative weekly measurement of 6MWD in chronic obstructive pulmonary disease (COPD) patients and healthy subjects.

Methods:

Twenty-six patients with COPD and nine age-matched healthy subjects were studied. Measurements were taken at baseline and after twelve weeks except for the 6MWD. The exercise measurements included a six-minute walking test (6MWT) and an incremental exercise test. Oxygen saturation, heart rate, and dyspnea will be monitored during all these tests.

Results:

At baseline there were significant differences between groups, except in age, body mass index, and oxygen saturation. After 12 weeks, there was no significant change in lung function in patients with COPD and healthy subjects. The 6MWD, peak oxygen uptake V̇O_2peak and anaerobic threshold increased significantly after training in both groups (P < 0.01). The averaged trace of the 6MWD of patients with COPD and healthy subjects was followed-up respectively by a logarithmic and linear fitting. 6MWD showed a plateau after eight weeks in patients with COPD, however, it increased continually overall in healthy subjects.

Conclusion:

Both patients with COPD and healthy subjects demonstrated functional responses to training but with somewhat different patterns in quality of the improvement of the 6MWD.

Systemic effects of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is associated with important extrapulmonary, or systemic, effects. There is systemic as well as pulmonary inflammation in COPD and this, together with systemic oxidative stress, contributes to their development. Skeletal muscle dysfunction contributes to exercise limitation. There is a loss of muscle mass and a reduction in the proportion of type 1 fibers. Sedentarism, hypoxia, corticosteroid therapy, nutritional depletion and systemic inflammation may contribute to its development. Weight loss is another important effect. It is associated with a worse prognosis, which changes with therapy and may be due to reductions in calorie intake, changes in intermediate metabolism and effects of systemic inflammation. Cardiovascular disease is a frequent cause of death in COPD and coronary artery disease, left ventricular failure and arrhythmias are systemic effects of COPD, as well as comorbidities sharing a common etiology. Exacerbations of COPD may increase the risk of coronary events by increasing the level of systemic inflammation. Osteoporosis is more common in COPD (even after adjusting for corticosteroid usage) and may be due to a combination of inactivity and the effects of systemic inflammation. COPD is also associated with systemic endothelial dysfunction and CNS abnormalities (including depression), which may also be due to the effects of systemic inflammation. These systemic effects respond to COPD treatments, including pulmonary rehabilitation, nutritional supplementation and inhaled corticosteroids, as well as specific drugs, such as bisphosphonates or diuretics. There is growing evidence that novel approaches, such as the use of statins, may also be of value.

Methods for the assessment of peripheral muscle fatigue and its energy and metabolic determinants in COPD

It has been well established that, in addition to the pulmonary involvement, COPD has systemic consequences that can lead to peripheral muscle dysfunction, with greater muscle fatigue, lower exercise tolerance and lower survival in these patients. In view of the negative repercussions of early muscle fatigue in COPD, the objective of this review was to discuss the principal findings in the literature on the metabolic and bioenergy determinants of muscle fatigue, its functional repercussions, as well as the methods for its identification and quantification. The anatomical and functional substrate of higher muscle fatigue in COPD appears to include lower levels of high-energy phosphates, lower mitochondrial density, early lactacidemia, higher serum ammonia and reduced muscle perfusion. These alterations can be revealed by contraction failure, decreased firing rates of motor units and increased recruitment of motor units in a given activity, which can be functionally detected by a reduction in muscle strength, power and endurance. This review article also shows that various types of muscle contraction regimens and protocols have been used in order to detect muscle fatigue in this population. With this understanding, rehabilitation strategies can be developed in order to improve the resistance to muscle fatigue in this population.

MRC chronic Dyspnea Scale: Relationships with cardiopulmonary exercise testing and 6-minute walk test in idiopathic pulmonary fibrosis patients: a prospective study

Background

Exertional dyspnea is the most prominent and disabling feature in idiopathic pulmonary fibrosis (IPF). The Medical Research Chronic (MRC) chronic dyspnea score as well as physiological measurements obtained during cardiopulmonary exercise testing (CPET) and the 6-minute walk test (6MWT) are shown to provide information on the severity and survival of disease.

Methods

We prospectively recruited IPF patients and examined the relationship between the MRC score and either CPET or 6MWT parameters known to reflect physiologic derangements limiting exercise capacity in IPF patients

Results

Twenty-five patients with IPF were included in the study. Significant correlations were found between the MRC score and the distance (r = -.781, p < 0.001), the SPO₂ at the initiation and the end (r = -.542, p = 0.005 and r = -.713, p < 0.001 respectively) and the desaturation index (r = .634, p = 0.001) for the 6MWT; the MRC score and VO₂ peak/kg (r = -.731, p < 0.001), SPO₂ at peak exercise (r = -. 682, p < 0.001), VE/VCO₂ slope (r = .731, p < 0.001), VE/VCO₂ at AT (r = .630, p = 0.002) and the Borg scale at peak exercise (r = .50, p = 0.01) for the CPET. In multiple logistic regression analysis, the only variable independently related to the MRC is the distance walked at the 6MWT.

Conclusion

In this population of IPF patients a good correlation was found between the MRC chronic dyspnoea score and physiological parameters obtained during maximal and submaximal exercise testing known to reflect ventilatory impairment and exercise limitation as well as disease severity and survival. This finding is described for the first time in the literature in this group of patients as far as we know and could explain why a simple chronic dyspnea score provides reliable prognostic information on IPF.

Impact of pulmonary system limitations on locomotor muscle fatigue in patients with COPD

We examined the effects of respiratory muscle work [inspiratory (W(r-insp)); expiratory (W(r-exp))] and arterial oxygenation (Sp(O(2))) on exercise-induced locomotor muscle fatigue in patients with chronic obstructive pulmonary disease (COPD). Eight patients (FEV, 48 +/- 4%) performed constant-load cycling to exhaustion (Ctrl; 9.8 +/- 1.2 min). In subsequent trials, the identical exercise was repeated with 1) proportional assist ventilation + heliox (PAV); 2) heliox (He:21% O(2)); 3) 60% O(2) inspirate (hyperoxia); or 4) hyperoxic heliox mixture (He:40% O(2)). Five age-matched healthy control subjects performed Ctrl exercise at the same relative workload but for 14.7 min ( approximately best COPD performance). Exercise-induced quadriceps fatigue was assessed via changes in quadriceps twitch force (Q(tw,pot)) from before to 10 min after exercise in response to supramaximal femoral nerve stimulation. During Ctrl, absolute workload (124 +/- 6 vs. 62 +/- 7 W), W(r-insp) (207 +/- 18 vs. 301 +/- 37 cmH(2)O x s x min(-1)), W(r-exp) (172 +/- 15 vs. 635 +/- 58 cmH(2)O x s x min(-1)), and Sp(O(2)) (96 +/- 1% vs. 87 +/- 3%) differed between control subjects and patients. Various interventions altered W(r-insp), W(r-exp), and Sp(O(2)) from Ctrl (PAV: -55 +/- 5%, -21 +/- 7%, +6 +/- 2%; He:21% O(2): -16 +/- 2%, -25 +/- 5%, +4 +/- 1%; hyperoxia: -11 +/- 2%, -17 +/- 4%, +16 +/- 4%; He:40% O(2): -22 +/- 2%, -27 +/- 6%, +15 +/- 4%). Ten minutes after Ctrl exercise, Q(tw,pot) was reduced by 25 +/- 2% (P < 0.01) in all COPD and 2 +/- 1% (P = 0.07) in healthy control subjects. In COPD, DeltaQ(tw,pot) was attenuated by one-third after each interventional trial; however, most of the exercise-induced reductions in Q(tw,pot) remained. Our findings suggest that the high susceptibility to locomotor muscle fatigue in patients with COPD is in part attributable to insufficient O(2) transport as a consequence of exaggerated arterial hypoxemia and/or excessive respiratory muscle work but also support a critical role for the well-known altered intrinsic muscle characteristics in these patients.

Muscle training with repetitive magnetic stimulation of the quadriceps in severe COPD patients

BACKGROUND

Previous studies have used electrical neuromuscular stimulation as a physical training method in patients with severe COPD. We introduce the use of the more tolerable magnetic stimulation for the same purpose, investigating the effectiveness of an eight-week protocol.

METHODS

Eighteen patients with severe COPD were randomly assigned to a magnetic stimulation training protocol, n=10, FEV(1)=30% (SD: 7) or to parallel clinical monitoring, control group, n=8, FEV(1)=35% (SD: 8). During eight weeks, patients were stimulated for 15min on each quadriceps femoris, three times per week. Quadriceps muscle strength and endurance measurements, quality-of-life questionnaires (SF36, SGRQ) and a six-minute walking test were all carried out before and after the training period in the stimulated and control subjects.

RESULTS

All patients completed the training with increasing intensity of stimulation, displaying a significant improvement in voluntary quadriceps strength (17.5% of the baseline value) and exercise capacity, with a mean increase of 23m in the six-minute walking test. The questionnaire scores showed greater increases in quality-of-life scores in the trained subjects compared to the controls, particularly in the physical function areas: mean increments in SF36 in "physical function": +26, "role limitations due to physical problems": +40 and "vitality": +17.5, while +13, -4 and +1, respectively in controls. Saint George's "Activity" score improved by 19.6 points, for 11.5 in controls.

CONCLUSIONS

In COPD patients who are limited due to dyspnoea, magnetic neuromuscular stimulation of the quadriceps constitutes a feasible training method for the lower limbs, with positive effects on the muscle function, effort capacity and perception areas.

Impact of preinduced quadriceps fatigue on exercise response in chronic obstructive pulmonary disease and healthy subjects

Exercise intolerance in chronic obstructive pulmonary disease (COPD) results from a complex interaction between central (ventilatory) and peripheral (limb muscles) components of exercise limitation. The purpose of this study was to evaluate the influence of quadriceps muscle fatigue on exercise tolerance and ventilatory response during constant-workrate cycling exercise testing (CWT) in patients with COPD and healthy subjects. Fifteen patients with COPD and nine age-matched healthy subjects performed, 7 days apart, two CWTs up to exhaustion at 80% of their predetermined maximal work capacity. In a randomized order, one test was performed with preinduced quadriceps fatigue and the other in a fresh state. Quadriceps fatigue was produced by electrostimulation-induced contractions and quantified by maximal voluntary contraction and potentiated twitch force (TwQpot). Endurance time and ventilatory response during CWT were compared between fatigued and fresh state. Endurance time significantly decreased in the fatigued state compared with the fresh condition in COPD (356 ± 69 s vs. 294 ± 45 s, P < 0.05) and controls (450 ± 74 s vs. 340 ± 45 s, P < 0.05). Controls showed significantly higher ventilation and end-exercise dyspnea scores in the fatigued condition, whereas, in COPD, fatigue did not influence ventilation or dyspnea during exercise. The degree of ventilatory limitation, as expressed by the V̇e/maximum voluntary ventilation ratio, was similar in both conditions in patients with COPD. We conclude that it is possible to induce quadriceps fatigue by local electrostimulation-induced contractions. Our findings demonstrate that peripheral muscle fatigue is an additional important factor, besides intense dyspnea, that limits exercise tolerance in COPD.

Skeletal muscle dysfunction in COPD: clinical and laboratory observations

COPD (chronic obstructive pulmonary disease), although primarily a disease of the lungs, exhibits secondary systemic manifestations. The skeletal muscles are of particular interest because their function (or dysfunction) not only influences the symptoms that limit exercise, but may contribute directly to poor exercise performance. Furthermore, skeletal muscle weakness is of great clinical importance in COPD as it is recognized to contribute independently to poor health status, increased healthcare utilization and even mortality. The present review describes the current knowledge of the structural and functional abnormalities of skeletal muscles in COPD and the possible aetiological factors. Increasing knowledge of the molecular pathways of muscle wasting will lead to the development of new therapeutic agents and strategies to combat COPD muscle dysfunction.

The “Oil Well Analogy” as a Comprehensive Interpretation of Factors Leading to Muscle Injury and Wasting

Muscle abnormalities involved in chronic obstructive pulmonary disease (COPD) or the changes leading to muscle wasting and cachexia in neoplastic patients have a remarkable clinical impact, but their study is complex and findings are sometimes paradoxical. In this review, the main factors influencing muscle wasting and muscle abnormalities found in chronic diseases such as COPD are regarded in the light of a comprehensive approach. All this changes work in a complex, multifactorial manner, and experimental or observational approaches must take this fact into consideration. Two concepts that may be helpful in this regard are the "muscle compartment theory," by which different muscle groups, individual muscles, or muscle areas may react differently to a variety of stimuli and pathogenic factors, and the "oil well analogy," which reflects the complexity and variability of the energy resource depletion mechanisms in cells and tissues, leading to structural remodeling and functional adaptation or impairment.

Exercise Capacity in Chronic Obstructive Pulmonary Disease: Mechanisms of Limitation

Patients with chronic obstructive pulmonary disease (COPD) are often caught in a downward spiral that progresses from expiratory flow limitation to poor quality of life and invalidity. Within this downward spiral, exercise tolerance represents a key intermediate outcome. As recently stated by the GOLD initiative, improvement in exercise tolerance is now rec ognized as an important goal of COPD treatment. This objective will be achieved only by a comprehensive understanding of the mechanism of exercise limitation in this disease. The objective of this paper is to review the mechanisms of exercise limitation in COPD and discuss their relative contribution to exercise intolerance in patients suffering from this disease.

An index for breathlessness and leg fatigue

The features of perceived symptoms causing discontinuation of strenuous exercise have been scarcely studied. The aim was to characterize the two main symptoms causing the discontinuation of heavy work in healthy persons as well as describe the growth of symptoms during exercise. Breathlessness (b) and leg fatigue (l) were assessed using the Borg CR10 Scale and the Borg CR100 (centiMax) Scale, during a standardized exercise test in 38 healthy subjects (24-71 years). The b/l-relationships were calculated for terminal perceptions (ERI(b/l)), and the growth of symptoms determined by power functions for the whole test, as well as by growth response indexes (GRI). This latter index was constructed as a ratio between power levels corresponding to a very strong and a moderate perception. In the majority (71%) of the test subjects, leg fatigue was the dominant symptom at the conclusion of exercise (P<0.001) and the b/l ratio was 0.77 (CR10) and 0.75 (CR100), respectively. The GRI for breathlessness and leg fatigue was similar, with good correlations between GRI and the power function exponent (P<0.005). In healthy subjects, leg fatigue is the most common cause for discontinuing an incremental exercise test. The growth functions for breathlessness and leg fatigue during work are, however, almost parallel.

Skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a debilitating disease characterized by inflammation-induced airflow limitation and parenchymal destruction. In addition to pulmonary manifestations, patients with COPD develop systemic problems, including skeletal muscle and other organ-specific dysfunctions, nutritional abnormalities, weight loss, and adverse psychological responses. Patients with COPD often complain of dyspnea on exertion, reduced exercise capacity, and develop a progressive decline in lung function with increasing age. These symptoms have been attributed to increases in the work of breathing and in impairments in gas exchange that result from airflow limitation and dynamic hyperinflation. However, there is mounting evidence to suggest that skeletal muscle dysfunction, independent of lung function, contributes significantly to reduced exercise capacity and poor quality of life in these patients. Limb and ventilatory skeletal muscle dysfunction in COPD patients has been attributed to a myriad of factors, including the presence of low grade systemic inflammatory processes, nutritional depletion, corticosteroid medications, chronic inactivity, age, hypoxemia, smoking, oxidative and nitrosative stresses, protein degradation and changes in vascular density. This review briefly summarizes the contribution of these factors to overall skeletal muscle dysfunction in patients with COPD, with particular attention paid to the latest advances in the field.

[Phenotypic heterogeneity of chronic obstructive pulmonary disease]

A functional definition of chronic obstructive pulmonary disease (COPD) based on airflow limitation has largely dominated the field. However, a view has emerged that COPD involves a complex array of cellular, organic, functional, and clinical events, with a growing interest in disentangling the phenotypic heterogeneity of COPD. The present review is based on the opinion of the authors, who have extensive research experience in several aspects of COPD. The starting assumption of the review is that current knowledge on the pathophysiology and clinical features of COPD allows us to classify phenotypic information in terms of the following dimensions: respiratory symptoms and health status, acute exacerbations, lung function, structural changes, local and systemic inflammation, and systemic effects. Twenty-six phenotypic traits were identified and assigned to one of the 6 dimensions. For each dimension, a summary is provided of the best evidence on the relationships among phenotypic traits, in particular among those corresponding to different dimensions, and on the relationship between these traits and relevant events in the natural history of COPD. The information has been organized graphically into a phenotypic matrix where each cell representing a pair of phenotypic traits is linked to relevant references. The information provided has the potential to increase our understanding of the heterogeneity of COPD phenotypes and help us plan future studies on aspects that are as yet unexplored.

[Dyspnea and handicap in chronic obstructive pulmonary disease: interaction of their mechanisms]

Today, dyspnea in chronic obstructive pulmonary disease (COPD) is attributed to thoracic distention secondary to bronchial obstruction and hyperventilation. It inevitably occurs during exercise, even in patients with little obstruction, when they are capable of the elevated and prolonged power output that necessitates substantial hyperventilation. Exercise intolerance is due mainly to dyspnea, but muscle fatigue is also involved, especially in COPD patients who are malnourished. Deterioration of muscle function follows a substantial reduction in daily physical activity. In malnourished and hypoxemic subjects, however, responsibility for this is attributed to diverse aggravating biological processes related to chronic low-grade inflammation and to accentuated oxidative stress. The drastic diminution of physical activity results from ventilatory and muscle impairment and from symptoms that make movement painful. Improvement of ventilatory and muscle function, however, does not lead to recovery that allows sufficient physical activity. The spiral of disengagement, a morbid, psychodynamic process, accompanies chronic diseases and has the strongest effect in patients who were not highly physically active before becoming ill. Improvement of this handicap therefore requires a comprehensive management of patients, not confined to the prescription of physical activity under medical supervision. The aim is to offer diverse treatment propositions that can produce sustainable behavioral change.

Perceptual and physiologic responses during treadmill and cycle exercise in patients with COPD

BACKGROUND

Although the cycle ergometer is the traditional mode for exercise testing in patients with respiratory disease, this preference over the treadmill does not consider perceptual responses. Our hypotheses were as follows: (1) the regression slope between breathlessness and oxygen consumption (Vo(2)) is greater on the treadmill than on the cycle ergometer; and (2) the regression slope between leg discomfort and Vo(2) is greater on the cycle ergometer than on the treadmill.

METHODS

Twenty patients (10 men/10 women) with COPD (mean +/- SD postbronchodilator FEV(1), 50 +/- 15% of predicted) used a continuous method to report changes in breathlessness and in leg discomfort during cycle and treadmill exercise.

RESULTS

Patients reported an earlier onset of breathlessness and leg discomfort during cycling. Peak ratings of breathlessness were higher on the treadmill, whereas peak ratings of leg discomfort were higher on the cycle ergometer. The regression slopes for breathlessness as a function of Vo(2) and of minute ventilation (Ve) were higher on the treadmill. The regression slopes between leg discomfort and Vo(2) were similar for treadmill and cycle exercise. Peak Vo(2) was significantly higher with treadmill exercise (mean Delta = 8%; p = 0.002).

CONCLUSIONS

Patients with COPD exhibit different perceptual and physiologic responses during treadmill walking and cycling. Although ratings of breathlessness are initially higher with cycling at equivalent levels of Vo(2), the changes in breathlessness as a function of physiologic stimuli (Vo(2) and Ve) are greater during treadmill exercise. Leg discomfort is the predominant symptom throughout cycling.

COPD as a systemic disease

Chronic obstructive pulmonary disease (COPD) represents an important and increasing burden throughout the world. Classically, COPD has been considered a respiratory condition only, mainly caused by tobacco smoking. However, COPD has important manifestations beyond the lungs, the so-called systemic effects. These include unintentional weight loss, skeletal muscle dysfunction, an increased risk of cardiovascular disease, osteoporosis, and depression, among others. Low-grade, chronic systemic inflammation is one of the key mechanisms underlying these systemic effects. Because these extra-pulmonary manifestations of COPD are common and/or may have significant implications for the patient wellbeing and prognosis, they warrant systematic screening and appropriate management in order to provide optimal medical care.

Randomized controlled trial of dietary creatine as an adjunct therapy to physical training in chronic obstructive pulmonary disease

RATIONALE

Skeletal muscle strength and bulk are reduced in patients with chronic obstructive pulmonary disease (COPD) and influence quality of life, survival, and utilization of health care resources. Exercise training during pulmonary rehabilitation (PR) can reverse some of these effects. In athletes and healthy elderly individuals, dietary creatine supplementation (CrS) has been shown to augment high-intensity exercise training, thereby increasing muscle mass.

OBJECTIVES

This article examines the effect of CrS on functional exercise capacity and muscle performance in people with COPD.

METHODS

One hundred subjects with COPD (mean [SD] age, 68.2 [8.2] yr; FEV(1), 44.0 [19.6] %predicted) were randomized to a double-blind, placebo-controlled, parallel group trial of CrS during 7 weeks of PR encompassing aerobic and resistance exercises. Subjects ingested creatine (22 g/d loading for 5 d; maintenance, 3.76 g/d throughout PR) or placebo. Baseline, postloading, and postrehabilitation measurements included pulmonary function, body composition, peripheral muscle strength, and functional performance (shuttle walking tests). A volunteer subgroup (n = 44) had pre- and postloading quadriceps muscle biopsies.

MEASUREMENTS AND MAIN RESULTS

Eighty subjects completed the trial (38 creatine, 42 placebo). All outcome measures significantly improved after PR. There were no significant differences between groups post-PR (mean [SD] change in incremental shuttle walk distance, 84 [79] m in the creatine group vs. 83.8 [60] m in the placebo group; P = 1.0; knee extensor work, 19.2 [16] Nm [Newton meters] in the creatine group vs. 19.5 [17] Nm in the placebo group; P = 0.9). Muscle biopsies showed evidence of creatine uptake.

CONCLUSIONS

This adequately powered, randomized, placebo-controlled trial shows that CrS does not augment the substantial training effect of multidisciplinary PR for patients with COPD. Clinical trial registered with https://portal.nihr.ac.uk/Pages/NRRArchiveSearch.aspx (NO123138126).

The etiology and management of intractable breathlessness in patients with advanced cancer: a systematic review of pharmacological therapy

Intractable breathlessness is a common, devastating symptom of advanced cancer causing distress and isolation for patients and families. In advanced cancer, breathlessness is complex and usually multifactorial and its severity unrelated to measurable pulmonary function or disease status. Therapeutic advances in the clinical management of dyspnea are limited and it remains difficult to treat successfully. There is growing interest in the palliation of breathlessness, and recent work has shown that a systematic, evidence-based approach by a committed multidisciplinary team can improve lives considerably. Where such care is lacking it may be owing to therapeutic nihilism in clinicians untrained in the management of chronic breathlessness and unaware that there are options other than endurance. Optimum management involves pharmacological treatment (principally opioids, occasionally oxygen and anxiolytics) and nonpharmacological interventions (including use of a fan, a tailor-made exercise program, and psychoeducational support for patient and family) with the use of parenteral opioids and sedation at the end of life when appropriate. Effective care centers on the patient's needs and goals. Priorities in breathlessness research include studies on: neuroimaging, the effectiveness of new interventions, the efficacy, safety, and dosing regimens of opioids, the contribution of deconditioning, and the effect of preventing or reversing breathlessness.

Ventilatory constraints and dyspnea during exercise in chronic obstructive pulmonary disease

Dyspnea (respiratory difficulty) and activity limitation are the primary symptoms of chronic obstructive pulmonary disease (COPD) and progress relentlessly as the disease advances, contributing to reduced quality of life. In COPD, the mechanisms of dyspnea are multifactorial, but abnormal dynamic ventilatory mechanics are believed to play a central role. In flow-limited patients with COPD, dynamic lung hyperinflation (DH) occurs during exercise and has serious sensory and mechanical consequences. In several studies, indices of DH strongly correlate with ratings of dyspnea intensity during exercise, and strategies that reduce resting hyperinflation (either pharmacological or surgical) consistently result in reduced exertional dyspnea. The mechanisms by which DH gives rise to exertional dyspnea and exercise intolerance are complex, but recent mechanistic studies suggest that DH-induced inspiratory muscle loading, restriction of tidal volume expansion during exercise, and consequent neuromechanical uncoupling of the respiratory system are key components. This review examines the specific derangements of ventilatory mechanics that occur in COPD during exercise and attempts to provide a mechanistic rationale for the attendant respiratory discomfort and activity limitation.