TY - JOUR T1 - Lighter than air: heliox breathing improves exercise tolerance in COPD JF - European Respiratory Review JO - EUROPEAN RESPIRATORY REVIEW SP - 1 LP - 3 DO - 10.1183/09059180.00000210 VL - 19 IS - 115 AU - P. Palange Y1 - 2010/03/01 UR - http://err.ersjournals.com/content/19/115/1.abstract N2 - Dyspnoea and reduced exercise tolerance are the hallmarks of chronic obstructive pulmonary disease (COPD). In the advanced phases of the disease the ability to exercise is mainly limited by the combination of a reduced ventilatory capacity, increased ventilatory requirement and lung dynamic hyperinflation. Importantly, the aforementioned respiratory mehanical abnormalities are well recognised causes of exertional dyspnoea in COPD [1]. However, in a substantial number of patients a heightened perception of leg effort may reduce tolerance to cycle-ergometer exercise, while dyspnoea appears to be the main symptom limiting the ability to walk [2]. Regardless of this, there would be little question that, in patients with severe COPD and particularly in those subjects with predominant emphysema, maximal exercise tolerance is markedly reduced because of ventilatory limitation, dynamic hyperinflation and dyspnoea sensation. Figure 1⇓ illustrates the lung mechanical abnormalities that cause dyspnoea and exercise intolerance in COPD. Airflow obstruction could be the result of intrinsic airways narrowing, as observed in chronic bronchitis, or may be the result of airways collapse due to loss of lung elastic recoil, as observed in emphysema. Importantly, both these anatomical alterations cause a reduction in expiratory flow reserve. When this occurs, breathing is usually accommodated to a higher lung volume, to prevent the unpleasant sensation arising from the central airways and to permit adequate ventilation. As a result, dynamic lung hyperinflation develops due to well-refined actions of various neural and mechanical mechanisms, presumably to achieve the best compromise between the minimum amount of expiratory flow limitation and the least load for the inspiratory muscles. Breathing under conditions of expiratory flow limitation is associated with an increased work of breathing (WOB) and could lead to two basic physiological consequences: 1) airways undergoing mechanical collapse trigger neural signals elaborated at the cortical level, i.e. dyspnoea sensation; … ER -