Energy metabolism in skeletal muscle during ischemia and reperfusion. Experimental and clinical aspects

Abstract: Microsurgical operations, using free vascularised transfer of tissues, induce an obligatory period of ischemia followed by reperfusion. The degree of ischemia and reperfusion injury is dependent on the ischemia time. To deminish the injury after skeletal muscle tissue transfers, a preservation method is needed all along with improved mechanistical knowledge. This is important especially in a situation where the aim of the transfer is a functioning unit and in circumstances where a long ischemia time is expeceted, such as complicated cases or during reoperations. The aim of this thesis was to evaluate the ischemia and reperfusion injury in the clinical and experimental situation with special reference to energy metabolism and to evaluate different treatments using energy metabolites as markers for the degree of injury.Muscle biopsies from patients having microsurgical muscle transfers were analysed for high energy phosphates, during ischemia and reperfusion, by high pressure liquid chromatography (HPLC) and by in vitro 31P- magnetic resonance spectroscopy (MRS). To evaluate different treatments, a model of pedicled rat rectus femoris muscle was developed where phosphorous metabolites and intracellular pH were analysed during ischemia and reperfusion by in vitro and in vivo 31P- MRS, continuously and noninvasively. Results from the clinical study showed a partial recovery of PCr to 79% of normal control after revascularisation and a mean ischemia time of 114 min (median 85 min). Furthermore, regression analysis showed a recovery of 60% after 3 h of ischemia and 1 h of reperfusion, in accordance with earlier experimental results, why it is of great importance to further elucidate the mechanisms behind ischemia and reperfusion injury, and to establish preservation methods for the muscle cell. Hypothermia of 9-12°C improved the energetic recovery after postischemic reperfusion with 22% regarding PCr and with 35% regarding ATP compared to room temperature (22-24°C). Intracellular pH was also improved after postischemic recovery (pH 6.88 in hypothermia , pH 6.55 at room temperature). Illumination with Singlet Oxygen Energy (SOE), (l= 634 nm) on skeletal muscle preserved in NaCl or Perfadex decreased the high energy phosphate degradation, thus improving the cellular energy status. Furthermore, SOE-illumination on the in vivo rat skeletal muscle model showed a decreased degradation of 21% regarding ATP during ischemia. SOE-illumination also improved postischemic energetic recovery as demonstrated with an improvement of 22% regarding PCr and with 20% regarding ATP, measured continuously by in vivo 31P MRS.This thesis has thus demonstrated in a novel approach mechanistic similarities between experimental and clinical energetic behavior of skeletal muscle during ischemia and reperfusion. It is also shown that muscle cell injury after ischemia and reperfusion can be deminished by hypothermia.Isolated skeletal muscle can be better preserved by illumination with SOE. Furthermore, skeletal muscle ischemia and reperfusion injury in the living animal can be significantly decreased by illumination with SOE.