Studies on small intestinal obstruction. VI. Blood circulation in moderately distended small bowel after obstruction

Feline small-bowel circulation was studied during in vitro homologous perfusion of denervated intestine after in vivo obstruction. The bowel specimens showed delayed compliance and, when compared with non-obstructed specimens, enhanced distensibility. Bowel specimens investigated during continuous distension had a normal regional vascular resistance and a normal capillary filtration coefficient (CFC) but a somewhat decreased oxygen utilization; artificial distension to 20 mmHg caused a resistance enhancement and a profound (80-90%) reduction of CFC but did not prevent oxygen consumption from attaining normal levels. An artificial distension occasions an augmentation of regional vascular resistance, whereas the distension caused by intestinal obstruction does not; the significance of this observation is discussed. Bowel specimens investigated after intra-operative decompression showed normal vascular resistance, normal CFC and normal oxygen consumption; artificial distension to 20 mmHg produced a resistance enhancement and a moderate (40-50%) reduction of CFC; oxygen consumption was not affected. Thus, an intra-operative decompression involves no augmentation of regional vascular resistance and seems to increase the ability of the capillary bed to withstand, with retained function, a renewed distension. After release of the distension, flow reduction and resistance enhancement persisted, whereas CFC returned to basal values in both groups of specimens; oxygen consumption remained on stable levels. It is emphasized that the persisting augmentation of resistance observed after decompression of the bowel is related to the in vitro situation, whereas in vivo intra-opertive decompression of obstructed bowel seems to involve no consequences of this kind. Some experiments featured fluid output to the gut lumen in the post-distension period; this observation is discussed. A normal rate of oxygen utilization accompanied the profound reduction of perfused capillary surface area noted in obstructed gut upon a moderate additional distension; possible mechanisms underlying this finding are discussed. It is concluded from the present study that a simple small-bowel obstruction, although not per se involving any serious threat to the bowel viability, renders the gut wall vulnerable to any further increment of distension or ischaemia. It is suggested that this is mainly the result of enhanced distensibility in the wall of the obstructed gut.