Ultimately, viability can be assessed only by transplantation of the organ. It is revascularized in a recipient animal from which the appropriate organ has been removed, and observations are then made on the ability of the preserved organ to maintain the life of the recipient animal. However, this is time consuming, and too costly for routine assessment of organ viability during the early stages of investigation of a new storage technique. A simpler method is required in the first instance.
Fortunately, in vitro techniques can be used. Under conditions of normothermic organ perfusion with blood or balanced electrolyte solutions, various tests of function can be studied, and where appropriate, mechanical activity can be observed and measured. In all cases biochemical changes occurring in the perfusate and cells can be measured, and histological, ultra-microscopical, and histochemical studies can be made on sections of the organ cut at the end of the experiment. These tests give a fairly good indication of any gross damage produced by any storage technique, but the absence of any observable damage is not necessarily indicative of a viable organ. Using these tests it is possible to eliminate rapidly grossly damaging methods of preservation. Only seemingly successful storage techniques are then tested by implanting the stored organ into a recipient.
With these methods of assessment of viability, investigations are being directed towards finding for any organ: the ideal perfi~sate, cryoprotectant, concentration of cryoprotectant, storage temperature, and technique of reaching this temperature.