RESPIRATORY RESPONSE TO ARM ELEVATION IN PATIENTS WITH CHRONIC AIR-FLOW OBSTRUCTION

We have shown that patients with chronic airflow obstruction (CAO) complain of disabling dyspnea when performing seemingly trivial tasks with unsupported arms. Surprisingly little is known about the metabolic and ventilatory responses to unsupported upper extremity activity even though some of the muscles of the upper torso and shoulder girdle are used to perform simple and complex everyday tasks as well as partake in ventilation. To determine the effect of simple arm elevation in 20 patients with CAO we studied their lung function, VO2, VCO2, and VE, with arms down at the side (AD), during 2 min with arms extended forward up to shoulder level (AE), and during recovery. To determine the pattern of ventilatory muscle recruitment we also measured endoesophageal (Ppl), gastric (Pg), and transdiaphragmatic (Pdl) pressures. In five of the patients the electromyographic signal (EMG) of the sternocleidomastoid (Sm) muscle was recorded and analyzed in its time domain (amplitude) and power spectrum density (median frequency). Within 30 s of arm elevation VO2, VCO2, and VE rose and remained elevated for 1 min after the arms were lowered. The increase in VE resulted from increases in respiratory rate and minimal rise in tidal volume (VT). With AE, FEV1 decreased by 5% (p < 0.02) but FRC increased by 2% (p < 0.05). Peak inspiratory pressure (Pi(max)) dropped from 54 +/- 4 to 48 +/- 4 cm H2O (p < 0.005); Pdi(max) remained unchanged. Immediately after raising the arms Pgl, inspiratory swing in Pdl (DELTA-Pdl), end-expiratory Ppl, and end-expiratory Pg increased significantly. During arm elevation EMG Sm amplitude increased significantly (272 +/- 65%) without changes in the median frequency. We conclude that in patients with CAO simple AE results in a significant increase in metabolic and ventilatory demand. The increase in ventilation is achieved by increases in respiratory rate with only a modest increase in tidal volume. In addition, ventilatory muscle recruitment was altered with increases in diaphragmatic and expiratory muscle contribution. The increased amplitude of EMG Sm suggests that some of the accessory muscles of the rib cage are also recruited during arm elevation. These findings may help explain the ventilatory limitations seen in patients with CAO when they use their arms for activities of daily living.