The diaphragm in COPD. Better than expected, but not good enough

Muscle metabolomics analysis reveals potential biomarkers of exercise‑dependent improvement of the diaphragm function in chronic obstructive pulmonary disease

Decreased diaphragm function is a crucial factor leading to reduced ventilatory efficiency and worsening of quality of life in chronic obstructive pulmonary disease (COPD). Exercise training has been demonstrated to effectively improve the function of the diaphragm. However, the mechanism of this process has not been identified. The emergence of metabolomics has allowed the exploration of new ideas. The present study aimed to analyze the potential biomarkers of exercise-dependent enhancement of diaphragm function in COPD using metabolomics. Sprague Dawley rats were divided into three groups: COPD + exercise group (CEG); COPD model group (CMG); and control group (CG). The first two groups were exposed to cigarette smoke for 16 weeks to establish a COPD model. Then, the rats in the CEG underwent aerobic exercise training for 9 weeks. Following confirmation that exercise effectively improved the diaphragm function, a gas chromatography tandem time-of-flight mass spectrometry analysis system was used to detect the differential metabolites and associated pathways in the diaphragm muscles of the different groups. Following exercise intervention, the pulmonary function and diaphragm contractility of the CEG rats were significantly improved compared with those of the CMG rats. A total of 36 different metabolites were identified in the comparison between the CMG and the CG. Pathway enrichment analysis indicated that these different metabolites were involved in 17 pathways. A total of 29 different metabolites were identified in the comparison between the CMG and the CEG, which are involved in 14 pathways. Candidate biomarkers were selected, and the pathways analysis of these metabolites demonstrated that 2 types of metabolic pathways, the nicotinic acid and nicotinamide metabolism and arginine and proline metabolism pathways, were associated with exercise-induced pulmonary rehabilitation.

Effect of Lung Volume Reduction Surgery on Respiratory Muscle Strength in Advanced Emphysema

Background: Long-term effects of lung volume reduction surgery (LVRS) on respiratory muscle strength and effects of age, sex, and emphysema pattern on these changes are unknown. Therefore, we aimed to determine the long-term effect of LVRS on respiratory muscle strength changes in severe emphysema. Methods: The National Emphysema Treatment Trial was a prospective controlled multicentered trial, comparing LVRS to optimal medical treatment on survival and maximal exercise capacity. We examined percentage change in maximum inspiratory pressure (MIP) from baseline to 36 months follow-up to determine impact of LVRS as well as age, sex, emphysema pattern and exercise capacity on changes in MIP compared to medical treatment. Results: LVRS individuals had significantly greater increases in MIP from baseline compared to medical individuals at all follow-ups (LVRS 19.8 ± 42.3%, medical 3.2 ± 29.3%, p<0.0001, 12 months). The LVRS group had significant decreases in total lung capacity (TLC), residual volume (RV), functional residual capacity (FRC) and RV/TLC compared to the medical arm at all follow-up periods. Males and individuals 65-70 years of age had significantly greater increases in MIP following LVRS compared to the medical arm at all follow-ups; this same relationship was seen at up to 24 months for low exercise capacity, upper lobe predominant emphysema. Conclusions: LVRS significantly increases inspiratory muscle strength up to 3 years post-operatively, with male sex, age 65-70 years and low exercise capacity, upper lobe predominant emphysema especially associated with increased MIP. Inspiratory muscle strength increases were associated with decreases in non-invasive markers of dynamic hyperinflation, suggesting that LVRS allows inspiratory muscles to return to their optimal length-tension relationship.

Lung hyperinflation in chronic obstructive pulmonary disease: mechanisms, clinical implications and treatment

Lung hyperinflation is highly prevalent in patients with chronic obstructive pulmonary disease and occurs across the continuum of the disease. A growing body of evidence suggests that lung hyperinflation contributes to dyspnea and activity limitation in chronic obstructive pulmonary disease and is an important independent risk factor for mortality. In this review, we will summarize the recent literature on pathogenesis and clinical implications of lung hyperinflation. We will outline the contribution of lung hyperinflation to exercise limitation and discuss its impact on symptoms and physical activity. Finally, we will examine the physiological rationale and efficacy of selected pharmacological and non-pharmacological 'lung deflating' interventions aimed at improving symptoms and physical functioning.

The role of spinal manipulation, soft-tissue therapy, and exercise in chronic obstructive pulmonary disease: a review of the literature and proposal of an anatomical explanation

The premise that lung function can regulate chest wall mobility is an accepted concept. Descriptions of the primary and accessory respiratory structures do not usually include spinal components as a part of these classifications. The case for including these components as a part of the respiratory mechanism and their role in the development of dyspnea and chest wall rigidity in chronic obstructive pulmonary disease (COPD) is reviewed. Mechanical impairment of the chest wall is a contributing factor in the prognosis of COPD. Reducing this impairment improves prognosis. Because spinal manipulation and soft-tissue therapy increase joint mobility and decrease muscle hypertonicity, respectively, applying these interventions to the chest wall in COPD could reduce chest wall rigidity, thereby improving breathing mechanics. Improvements in breathing mechanics reduce the work of the respiratory muscles and delay the onset of dyspnea. Exercise capacity is reliant on the ability to overcome activity-limiting dyspnea, which usually occurs prior to maximum exercise capacity being reached. Delaying the onset of dyspnea permits more exercise to be performed before dyspnea develops. Spinal manipulation and soft-tissue therapy have the potential to deliver such a delay. Because exercise tolerance is considered to be a strong predictor of quality of life and survival in COPD, any increase in exercise capacity would therefore improve prognosis for the disease.

Do obstructive and restrictive lung diseases share common underlying mechanisms of breathlessness?

This review tries to answer two main questions: (i) What are the neurophysiological underpinnings of the most commonly selected cluster descriptors which define the qualitative dimension of dyspnea in patients? (ii) How do mechanical constraints affect dyspnea? (iii) Do obstructive and restrictive lung diseases share some common underlying mechanisms? Qualitative dimensions of dyspnea, which allude to increased respiratory work/effort breathing, reflect a harmonious coupling between increased respiratory motor output and lung volume displacement in healthy subjects. Descriptors that allude to unsatisfied inspiration are the dominant qualitative descriptors in patients with a variety of respiratory diseases. It is possible that sensory feedback from a multitude of mechanoreceptors throughout the respiratory system (in the muscle, chest wall, airways and lung parenchyma) collectively convey information to the consciousness that volume/flow or chest wall displacement is inadequate for the prevailing respiratory drive. The data would lend support to the idea that: (i) an altered afferent proprioceptive peripheral feedback signals that ventilatory response is inadequate to the prevailing motor drive, reflecting neuromechanical uncoupling (NMU), (ii) mechanical constraints on volume expansion (dynamic restriction) play a pivotal role in dyspnea causation in patients with a variety of either obstructive or restrictive respiratory disorders, and (iii) all of the physiological adaptations that optimize neuromechanical coupling in obstructive and restrictive disorders are seriously disrupted so that an NMU underpins cluster descriptors of dyspnea which are similar in obstructed and in restricted patients.

[Limiting factors of exercise capacity in patients with COPD]

Chronic Obstructive Pulmonary Disease (COPD) is a major cause of morbidity and mortality worldwide. Moderate to severe COPD patients demonstrate severe impairments in exercise performance in daily activities, significantly affecting their quality of life. There are several causes for this limitation found in literature: air-flow limitation, lung hyperinflation, respiratory and peripheral muscles weakness, among others. In this study we intended to identify the potentially relevant factors that influence exercise performance in a group of moderate to severe COPD patients. We studied 24 male patients, 64,13 + 8,46 years old (46-83 years), FEV1: 46,96 + 12,99% predicted, FRC: 144,71 + 26,86% predicted, DLCO: 69,88 + 16,49 % predicted, PaO2: 78,25 + 7,82 mmHg, PaCO2: 40,78 + 4,28 mmHg. Patients performed an incremental symptom-limited cycle exercise. We correlated rest and exercise lung function parameters with peak oxygen uptake, maximal work rate and time span to exertion. The main contributors to exercise limitation were gas exchange abnormalities, ventilatory limitation and smaller values of body mass index. Rest lung hyperinflation didn't correlate with exercise performance. Dynamic exercise hyperinflation contributed greatly to exercise intolerance, through progressive restriction to tidal volume expansion necessary to deal with increasing exercise metabolic demands. Rest lung function parameters didn't correlate with exercise performance, stressing the importance of cardio-pulmonary exercise testing in the detection of exercise limitation factors in each patient. The identification of exercise limitation factors will certainly contribute to towards defining the best therapeutic approach in COPD patients.

Respiratory muscle fibres: specialisation and plasticity

Skeletal muscles are composed of fibres of different types, each type being identified by the isoform of myosin heavy chain which is expressed as slow 1, fast 2A, fast 2X, and fast 2B. Slow fibres are resistant to fatigue due to their highly oxidative metabolism whereas 2X and 2B fibres are easily fatiguable and fast 2A fibres exhibit intermediate fatigue resistance. Slow fibres and fast fibres are present in equal proportions in the adult human diaphragm while intercostal muscles contain a higher proportion of fast fibres. A small fibre size, abundance of capillaries, and a high aerobic oxidative enzyme activity are typical features of diaphragm fibres and give them the resistance to fatigue required by their continuous activity. Because of their fibre composition, intercostal muscles are less resistant to fatigue. The structural and functional characteristics of respiratory muscle fibres are not fixed, however, and can be modified in response to several physiological and pathological conditions such as training (adaptation to changes in respiratory load), adaptation to hypoxia, age related changes, and changes associated with respiratory diseases. The properties of respiratory muscle fibres can also be modified by pharmacological agents such as beta2 agonists and corticosteroids used for the treatment of respiratory diseases.

Dyspnoea in health and obstructive pulmonary disease : the role of respiratory muscle function and training

A consistent finding of recent research on respiratory muscle training (RMT) in healthy humans has been an attenuation of respiratory discomfort (dyspnoea) during exercise. We argue that the neurophysiology of dyspnoea can be explained in terms of Cambell's paradigm of length-tension inappropriateness. In the context of this paradigm, changes in the contractile properties of the respiratory muscles modify the intensity of dyspnoea predominantly by changing the required level of motor outflow to these respiratory muscles. Thus, factors that impair the contractile properties of the respiratory muscles (e.g. the pattern of tension development, functional weakening and fatigue) have the potential to increase the intensity of dyspnoea, while factors that improve the contractile properties of these respiratory muscles (e.g. RMT) have the potential to reduce the intensity of dyspnoea. In patients with obstructive pulmonary disease, functional weakening of the inspiratory muscles in response to dynamic lung hyperinflation appears to be a central component of dyspnoea. A decrease in the intensity of respiratory effort sensation (during exercise and loaded breathing) has been observed in both healthy individuals and patients with obstructive pulmonary disease after RMT. We conclude that RMT has the potential to reduce the severity of dyspnoea in healthy individuals and in patients with obstructive pulmonary disease, and that this probably occurs via a reduction in the level of motor outflow. Further work is required to clarify the role of RMT in the management of other disease conditions in which the function of the respiratory muscles is impaired, or the loads that they must overcome are elevated (e.g. cardiorespiratory and neuromuscular disorders).

Inspiratory muscle training in patients with COPD: effect on dyspnea, exercise performance, and quality of life

OBJECTIVE

The aim of the study was to assess the effect of target-flow inspiratory muscle training (IMT) on respiratory muscle function, exercise performance, dyspnea, and health-related quality of life (HRQL) in patients with COPD.

PATIENTS AND METHODS

Twenty patients with severe COPD were randomly assigned to a training group (group T) or to a control group (group C) following a double-blind procedure. Patients in group T (n = 10) trained with 60 to 70% maximal sustained inspiratory pressure (SIPmax) as a training load, and those in group C (n = 10) received no training. Group T trained at home for 30 min daily, 6 days a week for 6 months.

MEASUREMENTS

The measurements performed included spirometry, SIPmax, inspiratory muscle strength, and exercise capacity, which included maximal oxygen uptake (VO(2)), and minute ventilation (VE). Exercise performance was evaluated by the distance walked in the shuttle walking test (SWT). Changes in dyspnea and HRQL also were measured.

RESULTS

Results showed significant increases in SIPmax, maximal inspiratory pressure, and SWT only in group T (p < 0.003, p < 0.003, and p < 0.001, respectively), with significant differences after 6 months between the two groups (p < 0.003, p < 0.003, and p < 0.05, respectively). The levels of VO(2) and VE did not change in either group. The values for transitional dyspnea index and HRQL improved in group T at 6 months in comparison with group C (p < 0.003 and p < 0.003, respectively).

CONCLUSIONS

We conclude that targeted IMT relieves dyspnea, increases the capacity to walk, and improves HRQL in COPD patients.

Ventilatory limitations in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disorder characterized by dysfunction of the small and large airways, as well as by destruction of the lung parenchyma and vasculature, in highly variable combinations. Breathlessness and exercise intolerance are the most common symptoms in COPD and progress relentlessly as the disease advances. Exercise intolerance is multifactorial, but in more severe disease, ventilatory limitation is often the proximate exercise-limiting event. Multiple factors determine ventilatory limitation and include integrated abnormalities in ventilatory mechanics and ventilatory muscle function as well as increased ventilatory demands (as a result of gas exchange abnormalities) and alterations in the neuroregulatory control of breathing. Despite its heterogeneity, the pathophysiological hallmark of COPD is expiratory flow limitation. When ventilation increases in flow-limited patients during exercise, air trapping is inevitable and causes further dynamic lung hyperinflation (DH) above the already increased resting volumes. DH causes elastic and inspiratory threshold loading of inspiratory muscles already burdened with increased resistive work. It seriously constrains tidal volume expansion during exercise. DH compromises the ability of the inspiratory muscles to generate pressure, and the positive intrathoracic pressures likely contribute to cardiac impairment during exercise. Progressive DH hastens the development of critical ventilatory constraints that limit exercise and, by causing serious neuromechanical uncoupling, contributes importantly to the quality and intensity of breathlessness. The corollary of this is that therapeutic interventions that reduce operational lung volumes during exercise, by improving lung emptying or by reducing ventilatory demand (which delays the rate of DH), result in clinically meaningful improvement of exercise endurance and symptoms in disabled COPD patients.

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

Low exercise tolerance has a large influence on health status in chronic obstructive pulmonary disease and chronic heart failure. In addition to primary organ dysfunction, impaired skeletal muscle performance is a strong predictor of low exercise capacity. There are striking similarities between both disorders with respect to the muscular alterations underlying the impairment. However, different alterations occur in different muscle types. Histologic and metabolic data show that peripheral muscles undergo a shift from oxidative to glycolytic energy metabolism, whereas the opposite is observed in the diaphragm. These findings are in line with the notion that peripheral and diaphragm muscle are limited mainly by endurance and strength capacity, respectively. In both diseases, muscular impairment is multifactorially determined; hypoxia, oxidative stress, disuse, medication, nutritional depletion, and systemic inflammation may contribute to the observed muscle abnormalities and each factor has its own potential for innovative treatment approaches.

Effect of lung volume reduction surgery on diaphragm length in severe chronic obstructive pulmonary disease

Lung volume reduction surgery (LVRS) has been suggested as improving respiratory mechanics in patients with severe chronic obstructive pulmonary disease (COPD). We hypothesized that LVRS might lengthen the diaphragm, increase its area of apposition with the chest wall, and thereby improve its mechanical function. To determine the effect of bilateral LVRS on diaphragm length, we measured diaphragm length at TLC, using plain chest roentgenograms (CXRs), in 25 patients (11 males and 14 females) before LVRS and 3 to 6 mo after LVRS. A subgroup of seven patients (reference data) also had diaphragm length measurements made with CXRs, using films made within a year before their presurgical evaluation. Right hemidiaphragm silhouette length (PADL) and the length of the most vertically oriented portion of the right hemidiaphragm muscle (VDML) were measured. Diaphragm dome height was determined from the: (1) distance between the dome and transverse diameter at the manubrium; and (2) highest point of the dome referenced horizontally to the vertebral column. Patients also underwent spirometry, measurements of lung volumes and diffusion capacity, an incremental symptom-limited maximum exercise test, and measurements of 6 min walk distance (6MWD) and transdiaphragmatic pressures during maximum static inspiratory efforts (Pdimax sniff) and bilateral supramaximal electrophrenic twitch stimulation (Pditwitch) both before and 3 mo after LVRS. Patients were 58 +/- 8 yr of age, with severe COPD and hyperinflation (FEV1 = 0.68 +/- 0.23 L, FVC = 2.56 +/- 7.3 L, and TLC = 143 +/- 22% predicted). Following LVRS, PADL increased by 4% (from 13.9 +/- 1.9 cm to 14.5 +/- 1.7 cm; p = 0.02), VDML increased by 44% (from 2.08 +/- 1.5 cm to 3.00 +/- 1.6 cm, p = 0.01), and diaphragm dome height increased by more than 10%. In contrast, diaphragm lengths were similar in subjects with CXRs made before LVRS and within 1 yr before evaluation. The increase in diaphragm length correlated directly with postoperative reductions in TLC and RV, and also with increases in transdiaphragmatic pressure with maximal sniff (Pdimax sniff), maximal oxygen consumption (V O2max), maximal minute ventilation (V Emax), and maximum voluntary ventilation following LVRS. We conclude that LVRS leads to a significant increase in diaphragm length, especially in the area of apposition of the diaphragm with the rib cage. Diaphragm lengthening after LVRS is most likely the result of a reduction in lung volume. Increases in diaphragm length after LVRS correlate with postoperative improvements in diaphragm strength, exercise capacity, and maximum voluntary ventilation.

Lack of effects of recombinant growth hormone on muscle function in patients requiring prolonged mechanical ventilation: a prospective, randomized, controlled study

OBJECTIVE

To evaluate the benefit of recombinant human growth hormone administration on muscle strength and duration of weaning in critically ill patients undergoing prolonged mechanical ventilation.

DESIGN

Prospective, randomized, controlled, single-blind study.

SETTING

Intensive care unit.

PATIENTS

Twenty patients requiring > or = 7 days of mechanical ventilation for acute respiratory failure.

INTERVENTION

Random assignment to receive either 0.43 IU (approximately 0.14 mg) recombinant growth hormone/kg body weight/day (treated group), or saline (nontreated group) for 12 days.

MEASUREMENTS AND MAIN RESULTS

Nutritional support was guided by indirect calorimetry. Cumulative nitrogen balance was positive throughout the study period in the treated group 17.3 (44.9 +/- 17.3[SEM] g/12 days) vs. the nontreated group (-65.8 +/- 11.8 g/12 days) (p<.0001). Despite similar initial plasma concentrations, recombinant growth hormone supplementation resulted in marked increases in growth hormone, insulin like growth factor-1, and insulin concentrations (p<.05, .02, and .0001, respectively, vs. nontreated group). Body impedance determined net fat-free mass increased in the treated group (0.8 +/- 0.6 kg) vs. the nontreated group (-1.1 +/- O.5 kg) (p<.03). Initial peripheral muscle function, assessed by computer-controlled electrical stimulation of the adductor pollicis, was similarly lower in treated and nontreated groups than sex and age-matched normal controls, and decreased further during the study period. Arterial blood gases, cumulative total mechanical ventilation time, and number of hrs/day of mechanical ventilation during weaning were similar in both patient groups. Only three of the ten patients in each group were weaned from mechanical ventilation by day 12.

CONCLUSIONS

Daily administration of recombinant growth hormone in mechanically ventilated patients with acute respiratory failure promotes a marked nitrogen retention. However, this reaction is accompanied neither by an improvement in muscle strength nor by a shorter duration of ventilatory supports.

Effects of body position, hyperinflation, and blood gas tensions on maximal respiratory pressures in patients with chronic obstructive pulmonary disease

BACKGROUND

Inspiratory muscle strength in patients with chronic obstructive pulmonary disease (COPD) can be affected by mechanical factors which influence the length of the diaphragm, and by non-mechanical factors. The aim of the present study was to evaluate firstly the effects of body position on respiratory pressures and, secondly, to determine the relative contribution of age, body mass index (BMI), lung volumes, and arterial blood gas tensions to respiratory muscle strength.

METHODS

Thirty male patients with stable COPD (mean FEV1 40.4% predicted) participated in the study. Maximal inspiratory and expiratory mouth pressures (PImax, PEmax) and maximal inspiratory transdiaphragmatic pressures (PDI) in the sitting and supine position, lung function, and arterial blood gas tensions were measured.

RESULTS

Mean (SD) PImax in the sitting position was higher than in the supine position (7.1(2.3)kPa v 6.4(2.2)kPa respectively). In contrast, PDI in the sitting position was lower than in the supine position (10.0(3.5)kPa v 10.8(3.7)kPa respectively). PEmax was higher in the sitting position (9.3(3.0)kPa) than in the supine position (8.7(2.8)kPa). Significant correlations were found between inspiratory muscle strength on the one hand, and lung function parameters, BMI, and arterial blood gas tensions on the other.

CONCLUSIONS

Inspiratory muscle strength in patients with COPD is influenced by mechanical factors (body position, lung volumes) and non-mechanical factors (BMI, FEV1, and blood gases). PImax and PEmax are lower in the supine position while, in contrast to healthy subjects, PDI is higher in the supine position than in the sitting position.

Exercise in patients with chronic obstructive pulmonary disease

Sporadic visits to the local doctor followed sometimes by changes in oral and inhaled bronchodilators and occasionally by the addition of steroids frequently does little to significantly improve symptoms and function in the disabled patient with COPD. As in other chronic diseases, the management of these patients is facilitated by a team approach in conjunction with general rehabilitation principles. The rationale and practical implementation of such a programme has recently been outlined by the American Association of Cardiopulmonary Rehabilitation. These are multifaceted programmes but a key component, as outlined above, is exercise training. In this brief review the various approaches available have been described. Controversy still reigns regarding the optimal modes of training and there are important differences among the several approaches. Two main groups can be delineated. One emphasises the detailed definition of the impaired physiology with therapeutic measures targeted to specific defects. There is good documentation that, conversely, unstructured programmes that use treadmill and free range walking and cycling also improve endurance for walking. Upper extremity training is of additional benefit. Programmes with as little as three sessions per week of 1-2 hours of low intensity activity have achieved success so we know that simple programmes can be helpful. Moreover, without the necessity for complex testing and training methods these programmes can be implemented with relatively low costs. Future investigations to examine the relationship between improved exercise capacity for walking and arm exercise on the one hand, and the ease of performance of activities of daily living on the other, will help to reinforce the effectiveness of exercise programmes.