Respiratory responses to unsupported arm lifts paced during expiration.

Unsupported arm exercise endurance is reduced in both normal subjects and patients with chronic obstructive pulmonary disease in association with an increase in dyspnea and alterations in the pattern of respiratory muscle recruitment. Some report greater difficulty carrying out arm activity paced during the expiratory phase of respiration rather than during inspiration. The purpose of this study was to determine the effect of unsupported arm exercise lifts paced in phase with expiration (EUAL) on (a) diaphragm recruitment measured as the electromyographic amplitude (EMG-DI), (b) the pattern of thoracoabdominal motion measured with inductive plethysmography, and (c) the sensation of dyspnea measured with a 100 mm visual analog scale. Data were collected from 18 normal adult subjects at baseline and during EUAL. When compared with rest, EUAL resulted in significant increases in mean inspiratory and expiratory diaphragm EMG amplitudes, dyssynchronous thoracoabdominal motion, and dyspnea intensity. These changes in diaphragm recruitment and thoracoabdominal motion may in part explain reports of increased dyspnea intensity with unsupported arm exercise.