A new model for evaluation of thrombosis and ischaemia/reperfusion injury.

BACKGROUND: The purpose of the present study was to describe infarct size and platelet accumulation when reperfusion injury was combined with a thrombogenic lesion in the coronary artery. The left anterior descending artery was damaged in 11 pigs and subsequently occluded proximal to the lesion for 50 min, followed by 4 h of reperfusion. RESULTS: The infarct size/area at risk was 40 (35 63)%. Infarct size correlated with troponin-T-3 h (p=0.85, p<0.002), but not with creatine kinase-3 h. Platelet aggregation decreased by 34% (p<0.01) at 15 min of reperfusion, but returned to baseline. Platelet accumulation in the left ventricle was significantly higher in the area at risk (194 (157-206)%) compared to the right ventricle (137 (120-142)%); p<0.05). CONCLUSION: A decreased platelet reactivity and increased accumulation of platelets in the area at risk indicates that activated platelets become entrapped in the myocardium. Troponin-T was a better marker of myocardial damage than creatine kinase in this in vivo model with pigs.

Platelet activating factor antagonism in pure skin flaps exposed to ischaemia-reperfusion injury.

Platelet activating factor (PAF) is an inflammatory mediator that participates in neutrophil activation and adhesion to the endothelial cells. The PAF-antagonist (L-659.989) improves survival in myocutaneous flaps after ischaemia-reperfusion injury. To establish whether PAF antagonism improves survival in a pure skin flap, we subjected bilateral porcine buttock skin flaps (n = 14) to eight hours of ischaemia and 18 hours of reperfusion. L-659.989 or saline were given by local intra-arterial bolus infusion five minutes before reperfusion. There was no improvement in flap survival. Neutrophil accumulation as indicated by myeloperoxidase activity was increased in both groups compared with control tissue that had not been operated on (p < 0.01). There was no difference between treatment groups. Although it protected myocutaneous flaps, PAF antagonism did not protect pure skin flaps from ischaemia-reperfusion injury. A possible explanation is differences in flow-patterns that do not allow otherwise effective drugs to enter the area at risk, and so inhibit them from exerting a beneficial effect.

Aprotinin attenuates platelet accumulation in ischaemia-reperfusion-injured porcine skeletal muscle.

This purpose of this study was to evaluate the effect of aprotinin, a serine protease inhibitor, in ischaemia- and reperfusion-injured myocutaneous flaps and skin flaps. Flap survival, microcirculatory platelet accumulation, and regional blood flow were investigated in seventeen pigs which had been subjected to 8 h of ischaemia and 18 h of reperfusion. The pigs were randomly assigned to aprotinin treatment (n = 9) or saline (n = 8). In-vitro studies were performed to investigate the influence of aprotinin on the activated partial thromboplastin time. The survival of skeletal muscle correlated positively with the concentration of aprotinin (P = 0.02) and could not be explained by regional changes in blood flow. Platelet accumulation was decreased in aprotinin-treated muscle (P = 0.04). In-vitro (n = 10), 100 kallikrein inactivator units/ml aprotinin prolonged the activated partial thromboplastin time both in plasma (P = 0.001) and in blood (P = 0.002), suggesting an anticoagulant rather than a procoagulant effect. In conclusion, aprotinin at high concentrations may be beneficial for the survival of skeletal muscle and provides protection from platelet accumulation in the microcirculation of skeletal muscle exposed to ischaemia and reperfusion injury.

E-selectin and L-selectin blockade in pure skin flaps exposed to ischaemia and reperfusion injury.

The inflammatory recruitment of leucocytes is a main cause of tissue damage in ischaemia/reperfusion (I/R) injury. Under appropriate flow conditions, E-selectin and L-selectin participate in the initial deceleration of neutrophils (PMNs) on inflamed endothelial cells before transmigration of PMNs into the surrounding tissue. Previous work from our lab showed increased survival of I/R injured myocutaneous flaps after treatment with anti-E/L-selectin. In this study, we have evaluated a combined antibody to E-selectin and L-selectin (EL-246) in porcine pure skin flaps exposed to I/R injury. Buttock skin flaps were exposed to eight hours of ischaemia and 20 hours of reperfusion. EL-246 or saline was given intra-arterially into the flaps. Estimated surviving area was not improved in the treated group. The lack of effect of EL-246 supports our suspicion that different mechanisms are involved in I/R injury in myocutaneous flaps compared with pure skin flaps. As a certain shear stress must be present for the selectins to exert their effect, a possible explanation for the diverse results in muscle and skin might be different reflow patterns.

Wound contraction in an experimental porcine model.

Wound contraction is thought to be independent of site, and circular full-thickness skin wounds are though not to contract completely. To verify these statements four circular full-thickness skin wounds were created on each side of eight pigs and randomised to treatment with either split-thickness skin grafts, or healing by secondary intention under a hydrocolloid dressing. Time to healing, contraction, and final scar shape were evaluated. The median healing time was 12 days (range 6-18) in the grafted wounds and 30 days (range 15-45) in the secondarily healing wounds. There were significant differences in healing time between the different sites on the pigs. In the secondarily healing group, medial-caudal wounds healed in 21 (15-21) days compared with lateral wounds which healed in 36 (21-45) days (p < 0.005), while no differences were found in the grafted group. There was a clear relationship between site and contractility and shape of the scars in both treatment groups. Scars located on the lateral-caudal aspect of the pig were predominantly round and contracted only slightly. Scars located on the lateral aspect of the pig tended to be oval. Contraction was greatest in the medial scars and least in the lateral scars. Median contraction was 33% (range -2-63) in skin grafted wounds and 64% (range 42-82) in secondarily healed wounds. This randomised experiment showed that extent of wound contraction is dependent of site, and that circular wounds do heal with contraction.

Sedimentation of formed elements in distally ischaemic flaps.

Our aim was to find out whether thrombosis has a key role in distally ischaemic flaps and whether heparin improves flap survival in distally ischaemic myocutaneous and pure skin flaps in pigs. In experiment 1 we measured the concentration of coagulation factors in the venous effluent from both viable flaps and distally ischaemic flaps. In experiment 2 radioactively labelled blood components (red cells, platelets and fibrinogen) were injected intravenously and the distribution of each tracer was measured. In experiment 3 either heparin or saline was given as a local, continuous direct intra-arterial infusion. Fluorescein was used in all experiments to estimate the eventual flap survival. Our results indicate that thrombosis is not an important factor in distal ischaemia, and that heparin did not improve survival. Instead, there seems to be selective pooling of formed elements in the ischaemic portion of the flap.