CHANGES IN FUNCTIONAL RESIDUAL CAPACITY AND REGIONAL DIAPHRAGM LENGTHS AFTER UPPER ABDOMINAL-SURGERY IN ANESTHETIZED DOGS

The respiratory performance of the diaphragm may be altered by changes in mechanical or neural factors, or both, induced by upper abdominal surgery. We conducted this study to examine the effects of upper abdom inal surgery on postoperative respiratory function. We studied resting lengths of four diaphragm regions, three in the costal and one in the crural diaphragm, with biplane videoroentgenography in six dogs immed iately after upper abdominal surgery and up to 30 days postoperatively . Functional residual capacity was 16.7% smaller immediately after sur gery compared with values obtained in the same animals after 30 days. Simultaneously measured resting lengths of each of the diaphragm regio ns immediately after surgery were longer, on average by 8.3%, than 30 days postoperatively. During the postoperative course, resting diaphra gm lengths gradually and uniformly decreased as functional residual ca pacity increased. Phrenic nerve stimulation in four other dogs immedia tely after identical surgery resulted in large diaphragm shortening (f rom 42% to 55%), indicating that neither the diaphragm nor phrenic ner ves were injured by the surgical manipulation. We hypothesize that res piratory dysfunction after upper abdominal surgery may be, at least in part, attributed to a decreased central drive for breathing caused by activation of the afferent limb of an inhibitory reflex owing to stre tching of the diaphragm.