DIAPHRAGM FUNCTION DURING SIGHS IN AWAKE DOGS AFTER LAPAROTOMY

Pulmonary complications after upper abdominal surgery are usually ascr ibed to temporary postoperative impairment of diaphragm function, whic h may not originate from intrinsic, structural injury but from reflex inhibition of diaphragm contractility. Spontaneous breathing is interr upted periodically by sighs, even after upper abdominal surgery. If po stoperative dysfunction of the diaphragm arises from a reflexic inhibi tion, then the sigh should temporarily override the inhibition and res tore normal diaphragm function. We implanted sonomicrometer and electr omyogram transducers chronically in six dogs by laparotomy, then direc tly measured length, shortening, and electromyogram activity of costal and crural diaphragm segments, parasternal intercostal, and transvers us abdominis muscles an average of 8.7 (range, 1-16) d later during re sting tidal breathing and sighs. In each animal we analyzed a sequence of breaths, including a sigh, when costal or crural diaphragm contrac tility was abnormal. With each sigh, the shape and amplitude of costal and crural diaphragm segmental shortening improved abruptly, from 0.9 and 1.4% of baseline length (% L-BL) during resting breathing to 12.1 and 11.1% L-BL respectively, during sighs. The sighs were compared to CO2-stimulated breaths of equivalent tidal volume, which did not show either pattern or amplitude of shortening equivalent to sighs. We con clude that diaphragm dysfunction after laparotomy arises from a reflex inhibition, which is overridden abruptly to return diaphragm function briefly to normal during each spontaneous sigh.