Effects of prolonged cold injury on the subcutaneous microcirculation of the hamster. I. Technique, morphology and tissue oxygenation.

An animal model is described allowing for direct measurements of local tissue PO2, microhemodynamics and vascular density in the event of a prolonged non freezing cold injury. The model consists of implanting a transparent skin fold chamber in the dorsal skin fold in hamsters and of inserting two permanent indwelling catheters in jugular vein and carotid artery, respectively. The microcirculation was studied using a Wild Photomacroscope for photography and a platinum multiwire electrode for measurements of local PO2 in the conscious animal. After 72 h of recovery from anesthesia and surgery, the experimental was started with the animal immobilized. The decrease of local s.c. temperature was achieved by perfusing a heat exchanger with distilled H2O and Isopropanol 70% (1:1) at a rate of 81/min with the heat exchanger located directly beneath the aluminium frame of the chamber. With this technique, a decrease in local tissue temperature from 28 degrees C to 15 degrees C could be obtained within 15 min and was kept constant for 60 min. After photography of the microcirculation and local PO2-measurements, the local temperature was further reduced to 5 degrees C with 15 min. Sixty minutes later, the area exposed was slowly rewarmed from a level of 5 degrees C within 30 min. This procedure was repeated in intervals of 24 h over a period of five days. During the course of the experiments, local PO2 values shifted toward hypoxic or even anoxic values. Intravital microscopic observation revealed aggregate formation, stasis and obstruction of capillary flow associated with pronounced tissue anoxia after five cold exposures. This event resulted inevitably in tissue necrosis and scar formation after seven consecutive exposures to cold. It is concluded that this model can be used to study the effects of local non freezing cold injury in a precisely reproducible manner.