In patients with chronic obstructive pulmonary disease (COPD) the limitation on unsupported arm exercise (UAE) is predominantly respiratory muscle function-dependent. It is characterized by neuromechanical dysfunction (thoracoabdominal dyssynchrony) of the inspiratory muscles (diaphragm, accessory), superimposed by lung mechanics dysfunction. The undergoing mechanism is probably multifactorial. To study the relationship of resting pulmonary function and UAE performance in patients with COPD. Twenty-one patients, mean age 63 +/- 7 years, with COPD [forced expiratory volume in the first second (FEV1) 42 +/- 12% of predicted] underwent assessment of resting lung function (inspiratory capacity 57 +/- 17%; functional residual capacity 204 +/- 38% of predicted), maximal inspiratory pressure (67 +/- 14 cmH2O), upper arm circumference (30 +/- 2 cm), and symptom-limited cardiopulmonary UAE assessments. UAE consisted of bilateral anterior arm elevation to shoulder level at a rate of 40 arm strokes.minute-1. A series of stepwise multiple regression models were fitted to the data to predict exercise time from resting pulmonary function indices.
Results: Statistically significant correlations (r) were found between exercise time and inspiratory capacity (% of predicted) (r = 0.67, p = 0.0008), maximal inspiratory pressure (cmH2O) (r = 0.47, p = 0.03), upper arm circumference (r = 0.74, p = 0.0001), FEV1 (% of predicted) (r = 0.62, p = 0.0026), oxygen uptake (r = 0.56, p = 0.0085) and functional residual capacity (% of predicted) (r = -0.41, p = 0.06, borderline). Inspiratory capacity (% of predicted), functional residual capacity (% of predicted), upper arm circumference (cm) and FEV1 (% of predicted) explained 77% of the variance in exercise time. Therapeutic strategies that aim to increase inspiratory capacity or decrease functional residual capacity, or increase inspiratory muscle strength and upper arm/torso muscle endurance are likely to alleviate symptoms and improve UAE performance in patients with COPD.