AMINOPHYLLINE AND RESPIRATORY MUSCLE INTERACTION IN NORMAL HUMANS

The effects of intravenous infusion of aminophylline on respiratory mu scle interaction were examined in seven normal subjects breathing at r est. Rib cage (RC-Ap) and abdominal (AB-Ap) volume displacements, pleu ral (Ppl), gastric (Pg), and transdiaphragmatic (Pdi) pressure swings, and electromyographic activity of the diaphragm (Edi) and the paraste rnal (Eps) muscles were measured under control and during infusion of either aminophylline or placebo in a double-blind randomized manner. C ompared with placebo, aminophylline induced an increase in ventilation (p < 0.01) that was mainly accounted for by an increase in tidal volu me (p = 0.01). Aminophylline induced a significant and similar increas e in RC-Ap and AB-ap associated with increased Ppl and Pg swings (p = 0.002, and p < 0.01, respectively). On the contrary, no changes in end -expiratory RC and AB volume and in Ppl and Pg at end-expiration were observed, indicating that expiratory muscles did not contribute to the increase in tidal volume. Edi and Eps increased significantly with am inophylline, whereas Pdi/Edi ratio remained unchanged. We conclude tha t in normal humans breathing at rest: (1) aminophylline increases vent ilation, promoting larger tidal volume; (2) this effect is due to incr eased neural drive to inspiratory muscles; (3) aminophylline does not promote any appreciable expiratory muscle recruitment and distortion i n the pattern of chest wall motion.