Activity of lower intercostal and abdominal muscle after upper abdominal surgery.

The decrease in end-expiratory lung volume after upper abdominal surgery has been attributed, in part, to reflex spasm of the abdominal muscles. To examine the influence of abdominal surgery on abdominal muscle tone, electromyographic (EMG) activity of abdominal and lower intercostal muscle was compared before operation with that at 3 hr and at 24 hr after operation in 18 healthy patients undergoing elective gastric or biliary surgery. After operation, EMG activity increased markedly and showed a phasic pattern of activity associated with respiration in most patients. This was characterized by a progressive increase in EMG activity during expiration with an abrupt decrease at the onset of inspiration. We conclude that increased expiratory activity in abdominal and lower intercostal muscle may be responsible for the decrease in lung volumes that occurs after upper abdominal surgery.