The bovine pericardial xenograft: II. Effect of tethering or pressurization during fixation on the tensile viscoelastic properties of bovine pericardium.

Our previous article suggested that control of the extensibility of aldehyde-fixed pericardium could be achieved by controlling shrinkage during fixation. Therefore, to prevent shrinkage, we have used sandpaper-lined plexiglass plates to clamp circular samples of bovine pericardium during fixation in glutaraldehyde, tethering them at their original dimensions. As well, we have applied transmural pressures of 50 or 100 mm Hg during fixation using a hydraulic column of glutaraldehyde solution. Strips cut at 0 degree, 30 degrees, 60 degrees, and 90 degrees to the base-to-apex cardiac direction have been examined for cyclic stress-strain response, stress relaxation, plastic deformation, and fracture behavior. Under physiological stresses, tethered and pressure-fixed materials were both nearly isotropic. Tethering during fixation produced a material with extensibility nearly identical to that of fresh tissue. Plastic deformation during cyclic loading was reduced below that seen in simple fixation while stress relaxation was unchanged. Pressure-fixation produced reduced extensibility similar to that produced in porcine aortic valve leaflets. Plastic deformation and stress relaxation were both markedly reduced. Pressure-fixation reduced the strain at fracture, but fracture behavior was otherwise unaffected. Tethering and pressure-fixation offer attractive means to control the mechanical behavior of bovine xenograft materials.

Cystadenocarcinoma of the pancreas.

The case presented herein has two exciting aspects. First, the cystadenocarcinoma may have developed in a previously existing pseudocyst secondary to trauma 4 years earlier. The history of trauma certainly pointed the author to a diagnosis of pseudocyst. The possibility has to be entertained that a long dormant pseudocyst underwent cystadenomatous and, ultimately, cystadenocarcinomatous change. The acute nature of the patient's clinical problem seems explainable on the basis of recent hemorrhage. The second point is more gratifying. The identification of omental spread at the time of the first operation led to a second and ultimately a third look in this young patient, with a fortunate result. It is only fair to restate the concept that the results in the treatment of malignant disease are more strongly influenced by the "biologic predeterminism" of the tumor than by any of our surgical manipulations [18]. Nonetheless, an aggressive approach to resectable disease in young patients appears justified.