Introduction
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COPD is a progressive disease characterised by minimally reversible airflow limitation. The main feature of COPD is the inability of patients to cope with their activities of daily life because of shortness of breath. Although the pathophysiological mechanisms involved in the development of dyspnoea and poor exercise tolerance in patients with COPD are complex, dynamic lung hyperinflation (DLH) plays a central role [1]. DLH has a static component, which is due to the destruction of pulmonary parenchyma and loss of elastic recoil by the lung; and a dynamic component, which occurs when patients with COPD breathe in before achieving a complete exhalation. Airflow limitation and DLH are the main causative factors of the dyspnoea occurring in COPD patients. DLH is tightly linked to dyspnoea and exercise tolerance. In the DLH of COPD, the residual volume increases because of airflow limitation related to exertion. DLH is expressed as decreased inspiratory capacity (IC) and increased functional residual capacity (FRC) due to a continually increasing end-expiratory lung volume [2, 3]. The major consequence of DLH is an increased ventilatory workload and decreased pressure-generating capacity by the inspiratory muscles, despite compensatory mechanisms [4].
The diaphragm is the main muscle employed for respiration. Patients with emphysema or COPD manifest major changes in the mass, thickness, and area of the diaphragm. Diaphragmatic contractions produce muscle shortening and thickening. Ultrasonography has been recently proposed for use in assessing both diaphragmatic excursions [5-7] and diaphragmatic thickness at different lung volumes [8]. The association between thickening of the diaphragm and diaphragmatic effort, however, is tenuous; ultrasonography measurements of diaphragmatic thickness explain only one-third (or less) of the variability in inspiratory efforts [9, 10]. On the other hand, ultrasonographic assessment of excursions of the right diaphragm shows high intra- and interobserver reliability [11]. Reduced movements of the diaphragm are a major risk factor for increased mortality in patients with COPD [12]. However, the relationship between diaphragmatic mobility and DLH remains unclear in patients with COPD. The primary purpose of this study was to evaluate the difference between the diaphragmatic excursions of patients with COPD versus control participants. The secondary purpose was to evaluate the effects of decreased diaphragmatic excursion on exercise tolerance and DLH in COPD patients.
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