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.

Correlations between dyspnea, diaphragm and sternomastoid recruitment during inspiratory resistance breathing in normal subjects.

The purpose of this study was to determine the relationship between recruitment of the DI and SM muscles measured as EMG signal amplitudes, the pattern of respiratory muscle recruitment measured with inductive plethysmography, and the intensity of the sensation of dyspnea, measured with 100 mm VAS. Eighteen normal subjects between the ages of 33 and 47 breathed under two conditions: normal controlled breathing and breathing against an inspiratory resistance at 60 percent of their maximal inspiratory pressure (MIP). The PM, RR, duty cycle (TI/TTOT, and VT were held constant. During resistance breathing, VAS dyspnea was increased when EMG-DI decreased; EMG-SM increased in association with the sensation of dyspnea. During inspiratory resistance breathing, dyspnea markedly increased and rib cage and accessory muscle recruitment was the predominant pattern of breathing. These data suggest that dyspnea may be associated with the recruitment of the accessory respiratory muscles rather than the recruitment of the diaphragm.