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.peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=ierx20status: publishe

Differences in respiratory muscle activity during cycling and walking do not influence dyspnea perception in obese patients with COPD

In patients with combined obesity and chronic obstructive pulmonary disease (COPD), dyspnea intensity at matched work rates during weight-supported cycling and weight-bearing walking is similar, despite consistent metabolic differences between test modalities. The present study examined the influence of differences in activity of the diaphragm and abdominal muscles during cycling and walking on intensity and quality of dyspnea at matched ventilation in obese patients with COPD. We compared respiratory muscle activity patterns and dyspnea ratings during incremental cycle and treadmill exercise tests, where work rate was matched, in 12 obese (body mass index 36.6 ± 5.4 kg/m(2); mean ± SD) patients with moderate COPD. We used a multipair electrode-balloon catheter to compare electromyography of the diaphragm and esophageal, gastric, and transdiaphragmatic pressures during the two exercise tests. Ventilation, breathing pattern, operating lung volumes, global respiratory effort, and electrical activation of the diaphragm were similar across exercise modalities for a given work rate. The cycling position was associated with greater neuromuscular efficiency of the diaphragm (P < 0.01), greater diaphragm use (P < 0.01) measured by the ventilatory muscle recruitment index, and less expiratory muscle activity compared (P < 0.01) with treadmill walking. However, intensity and quality of dyspnea were similar between exercise modalities. In obese patients with COPD, altered respiratory muscle activity due to body position differences between cycling and walking did not modulate perceived dyspnea when indirect measures of respiratory neural drive were unchanged.status: publishe

Ventilation Distribution Heterogeneity at Rest as a Marker of Exercise Impairment in Mild-to-Advanced COPD

Abstract The difference between total lung capacity (TLC) by body plethysmography and alveolar volume (VA) from the single-breath lung diffusing capacity measurement provides an index of ventilation distribution inequalities in COPD. The relevance of these abnormalities to dyspnea and exercise intolerance across the continuum of disease severity remains unknown. Two-hundred and seventy-six COPD patients distributed across GOLD grades 1 to 4 and 67 healthy controls were evaluated. The "poorly communicating fraction" (PCF) of the TLC was estimated as the ratio (%) of TLC to VA. Healthy subjects showed significantly lower PCF values compared to GOLD grades 1 to 4 (10 ± 3% vs. 17 ± 8% vs. 27 ± 10% vs. 37 ± 10% vs. 56 ± 11%, respectively; p < 0.05). Pulmonary gas exchange impairment, mechanical ventilatory constraints and ventilation-corrected dyspnea scores worsened across PCF tertiles (p < 0.05). Of note, GOLD grades 1 and 2 patients with the highest PCF values had pronounced exercise ventilatory inefficiency and dyspnea as a limiting symptom. In fact, dyspnea was a significant contributor to exercise limitation only in those with "moderate" or "extensive" PCF (p < 0.05). A receiver operating characteristics curve analysis revealed that PCF was a better predictor of severely reduced maximal exercise capacity than traditional pulmonary function indexes including FEV1 (area under the curve (95% confidence interval) = 0.85 (0.81-0.89), best cutoff = 33.4%; p < 0.01). In conclusion, PCF is a readily available functional marker of gas exchange and mechanical abnormalities relevant to dyspnea and exercise intolerance across the COPD grades.status: publishe

Inspiratory muscle training reduces diaphragm activation and dyspnea during exercise in COPD

Among patients with COPD, those with the lowest maximal inspiratory pressures experience greater breathing discomfort (dyspnea) during exercise. In such individuals, inspiratory muscle training (IMT) may be associated with improvement of dyspnea but the mechanisms for this are poorly understood. Therefore, we aimed to identify physiological mechanisms of improvement in dyspnea and exercise endurance following inspiratory muscle training (IMT) in patients with COPD and low maximal inspiratory pressure (Pi,max). The effects of 8 weeks of controlled IMT on respiratory muscle function, dyspnea, respiratory mechanics, and diaphragm electromyography (EMGdi) during constant-work rate cycle exercise were evaluated in patients with activity-related dyspnea (Baseline Dyspnea Index <9). Subjects were randomized to either IMT or a sham training control group (n=10 each). Twenty subjects (FEV= 47{plus minus}19 %predicted; Pi,max= -59{plus minus}14 cmHO; cycle ergometer peak work rate= 47{plus minus}21 %predicted) completed the study; groups had comparable baseline lung function, respiratory muscle strength, activity-related dyspnea and exercise capacity. IMT, compared with control, was associated with greater increases in inspiratory muscle strength and endurance, with attendant improvements in exertional dyspnea and exercise endurance time (all p<0.05). After IMT, EMGdi expressed relative to its maximum (EMGdi/EMGdi,max) decreased (p<0.05) with no significant change in ventilation, tidal inspiratory pressures, breathing pattern and operating lung volumes during exercise. In conclusion, IMT improved inspiratory muscle strength and endurance in mechanically compromised patients with COPD and low Pi,max. The attendant reduction in EMGdi/EMGdi,max helped explain the decrease in perceived respiratory discomfort despite sustained high ventilation and intrinsic mechanical loading over a longer exercise duration.status: publishe