Breathe review bronch therapy.qxd 21/05/2008 16:19 Page 2 This article has been adapted from an ERS Research Seminar held in Como, Italy in 2007. The original slides and other material can be found at www.ers-education.org D.E. O'Donnell Bronchodilator therapy in Professor of Medicine and Physiology COPD: physiological effects Division of Respiratory and Critical Care Medicine Queen's University Richardson House 102 Stuart Street K7L 2V6 Kingston, ON Canada Fax: 1 6135491459 Email: [email protected] Competing interests The author has served on advisory boards, accepted speaker’s fees and received research funding from GlaxoSmithKline, Pfizer and Boehringer Ingelheim. Provenance Adapted from an ERS Research Seminar Educational aims k To review current concepts of the mechanisms of symptom relief and improved exercise tolerance following pharmacological treatment in chronic obstructive pulmonary disease (COPD). k To examine the relative responsiveness of new physiological outcome parameters in clinical trials. Summary Bronchodilator therapy is the first step in improving dyspnoea and exercise endurance in patients with COPD. Recent studies have challenged the long-held view that airway obstruc- tion in COPD is irreversible. We now know that even in the setting of minor or no change in traditional spirometry, bronchodilator therapy is associated with consistent, and often impressive, reduction in lung hyperinflation. This pharmacological lung volume reduction is linked to improved inspiratory muscle function and enhanced neuro- mechanical coupling of the respiratory system during activity, even in those with advanced disease. Moreover, these improvements in dynamic mechanics provide a sound physiological rationale for observed bronchodilator-induced improvements in the important patient-centred outcomes of reduced dyspnoea and activity limitation. 342 Breathe | December 2005 | Volume 2 | No 2 Breathe review bronch therapy.qxd 21/05/2008 16:19 Page 3 COPD feature: Bronchodilator therapy in COPD: physiological effects as measured by "trough", or morning, pre-bron- Figure 1 Flow–volume curves pre- and post- Vmax chodilator EELV or IC [1, 2, 7, 14] Combined long- acting bronchodilators have additive effects on bronchodilator. V’max: maximal lung volume deflation [14]. flow; BD: bronchodilator. A recent mechanical study on the mecha- nisms of dyspnoea relief following therapy with Flow the long-acting bronchodilator tiotropium Volume showed that release of cholinergic tone was IC pre-BD associated with improved airway conductance at IC post-BD all lung volumes from total lung capacity to resid- ual volume (RV). Static elastic recoil of the lung was unchanged after acutely administered Educational questions tiotropium, and expiratory timing during sponta- 1. How do you explain the clin- neous resting breathing was unaffected. Lung Bronchodilator therapy ical observation that bron- deflation, therefore, primarily reflected improve- chodilator therapy can relieve Recent international guidelines have correctly ments in the mechanical time constants for lung highlighted dyspnoea alleviation and improve- emptying (i.e. reduced airway resistance). The dyspnoea in COPD in the ment in exercise tolerance as among the most main impact of bronchodilator therapy is, there- absence of an associated important management goals in COPD. fore, on the dynamically determined resting EELV change in FEV1? All classes of bronchodilators act by relaxing through pharmacological manipulation of airway 2. How do you explain the find- airway smooth muscle tone. Improvements in resistance. ing that following bronchodila- forced expiratory volume in one second (FEV1; Improvements in resting IC, which indirectly tor therapy in COPD, breathing beyond the natural variability of the measure- signify reduced EELV, have been shown to occur pattern during exercise ment) after inhaled bronchodilators signify as a result of treatment with all classes of bron- becomes slower and deeper? reduced resistance in the larger airways, as well chodilators (figure 2) [1–14]. A bronchodilator- as in alveolar units, with rapid time constants for induced increase in the resting IC (indicating lung emptying. In more advanced COPD (in con- reduced lung hyperinflation), in the order of 0.3 L trast to asthma), post-bronchodilator increases in or ~10–15% predicted (or 15–17% of baseline FEV1 mainly occur as a result of lung volume value), appears to be clinically meaningful and recruitment: the ratio of FEV1 to forced vital corresponds with important improvements in capacity is unaltered or may actually decrease in exertional dyspnoea, and exercise endurance response to bronchodilators [1–14]. Recent stud- measured during constant work-rate cycle exer- ies have shown that substantial reductions cise at 60–75% of the patients' pre-determined (>0.5 L) in end-expiratory lung volume (EELV) and maximal work rate [1–3]. improvements in inspiratory capacity (IC) can A number of studies have shown that bron- occur after acute short- and long-acting bron- chodilator therapy, alone or in combination with chodilator treatment in the presence of only mod- inhaled corticosteroids, does not alter the rate of est improvements in FEV1 (figure 1). Long-acting dynamic hyperinflation (or air trapping) during bronchodilators have been shown to be exercise [1–3]. In fact, the magnitude of the rest- associated with sustained lung volume reduction to-peak exercise reduction in IC may actually Figure 2 [6] SABD SABD Responses to bronchodilators in COPD. SABD: short-acting bron- [4] SABD SABD chodilator; LABA: long-acting β- agonist; LAAC: long-acting anti- [10] LABA LABA cholinergic; ICS: inhaled corticos- teroid. : crossover study; : parallel group study. [Ref] [1] LAAC LAAC [2] LAAC LAAC [13] ICS/LABA ICS/LABA 0 0.1 0.2 0.3 0.4 0.5 0 30 60 90 120 150 180 Change in IC L Change in endurance time s Breathe | June 2008 | Volume 4 | No 4 343 Breathe review bronch therapy.qxd 21/05/2008 16:19 Page 4 COPD feature: Bronchodilator therapy in COPD: physiological effects Suggested answers Bronchodilator responses in COPD 1: Bronchodilator therapy • Volume (functional residual capacity, RV) and flow responses (FEV1) to bronchodilators are independent [5] facilitates lung emptying • Bronchodilators often do not abolish expiratory flow limitation [9–13] and reduces air trapping. • IC responses are more likely in patients with resting expiratory flow limitation (IC <80% pred) [6] The resultant improvement • IC responses are more pronounced in those with expiratory flow limitation and severe resting hyperinflation [5, 6] in inspiratory muscle func- • Changes in IC correlate better with improved outcomes than changes in FEV1 [1, 4, 13] tion and neuromechanical coupling of the respiratory increase as a result of the higher levels of ventila- elastic loading of the inspiratory muscles, which system contribute to dysp- tion permitted by bronchodilator therapy. resulted in a reduced work and oxygen cost of noea relief. This pharmaco- However, because of recruitment of the IC at rest, breathing, compared with placebo [3]. A reduced logical lung volume reduc- the dynamic EELV at peak exercise is lower, in inspiratory threshold load, reflecting reduced intrinsic positive end-expiratory pressure, would tion can occur in the absolute terms, than the value obtained at the break-point of exercise during the placebo arm of be expected to enhance neuromechanical cou- absence of change in FEV1, the treatment. In other words, bronchodilator pling of the respiratory system during exercise. particularly in advanced treatment (compared with placebo) is associated The strongest correlate of improved exercise COPD. with a parallel downward shift in the EELV over endurance in a number of bronchodilator trials 2: In COPD, IC represents the course of the exercise test. has been reduced exertional dyspnoea intensity the true operating limits for Improvements in the resting IC (as % pred) [9–13]. Several bronchodilator studies have tidal volume expansion dur- following bronchodilator therapy has been shown shown that reduced dyspnoea ratings at a stan- ing exercise. Recruitment of to correlate well with: 1) improved peak symptom- dard exercise time correlated well with reduced IC (which reflects reduced limited oxygen uptake; 2) increased peak tidal operating lung volumes (reduced EELV and an air trapping) following bron- volume; 3) reduced dyspnoea ratings; and 4) increased inspiratory reserve volume) and chodilatation allows for increased endurance time during constant work- improved breathing pattern (increased tidal vol- greater tidal volume expan- rate cycle exercise testing in moderate-to-severe ume and reduced breathing frequency) [1, 4, 13]. sion during exercise, with COPD patients [1, 4, 13]. In all of the studies, The emerging evidence supports the idea that consequent reduced breath- increased resting IC permitted greater tidal vol- the beneficial effects of bronchodilators on respi- ing frequency. ume expansion with reduced breathing frequency ratory sensation in COPD patients are ultimately throughout exercise [9–13]. Moreover, in a recent related to enhanced neuromechanical coupling mechanical study, tiotropium was found to be of the respiratory system as a result of improved associated with reduced airways resistance and dynamic ventilatory mechanics. References 1. O'Donnell DE, Flüge T, Gerken F, et al. Effects of tiotropium on lung hyperinflation, dyspnoea and exercise tolerance in COPD. Eur Respir J 2004; 23: 832–840. 2. Maltais