Relationship between pulmonary function and unsupported arm exercise in patients with COPD

Exercise intolerance is a common feature in patients with chronic obstructive pulmonary disease (COPD) and may have only a weak relationship to the lung function impairment [1, 2]. Interestingly, patients with COPD may show different metabolic and ventilatory responses during arm exercise, particularly unsupported arm exercise (UAE), as opposed to leg exercise [3], suggesting that different mechanisms are responsible for these exercise limitations. UAE is considered a respiratory muscle function-dependent activity, with greater dependence on the activation of the inspiratory muscles (i.e. diaphragm, accessory muscles) than other types of exercise [4]. Many patients with COPD are unable to shift to diaphragm breathing during UAE and to tolerate the increased ventilatory and non-ventilatory demand placed on the respiratory apparatus [5]. This results in respiratory muscle derangement and severe dyspnea [6]. The respiratory muscle derangement during UAE may be adversely affected by the resting lung function impairment. CELLI et al. [7] showed that the likelihood of thoracoabdominal dyssynchrony during UAE increases as airflow obstruction worsens. Interestingly, MARTINEZ et al. [8] reported a strong negative linear correlation between the rise in transdiaphragmatic pressure and baseline diaphragm strength during UAE in patients with isolated diaphragmatic weakness but no airflow obstruction, confirming the importance of diaphragm function during UAE. EPSTEIN et al. [9] reported that in patients with severe COPD resting hyperinflation and, to a lesser degree, the force reserve of