Real-Time Monitoring of Mitochondrial NADH and Microcirculatory Blood Flow in the Spinal Cord

Abstract

We developed a real-time, in vivo monitoring system for the evaluation of spinal cord viability in rats during spinal cord ischemia. The aim of the present study was to apply a real-time multiparametric monitoring system in a rat spinal cord model exposed to ischemia or mechanical compression. The evaluation of spinal cord integrity during spine surgeries is highly important, as it enhances the potential to prevent secondary irreversible damage to the spinal cord tissue. Mitochondrial NADH redox state is the most sensitive parameter for tissue oxygenation state and, together with microcirculatory blood flow, can estimate the metabolic status of the spinal cord tissue. We applied the Tissue Vitality Monitoring System (TVMS) that includes optical fibers for the simultaneous monitoring of the spinal cord blood flow (SCBF) using laser Doppler flowmetry, and the mitochondrial NADH fluorescence using the fluorometric technique. Additionally, systemic arterial blood pressure was measured. Two models involving the interruption of the spinal blood flow were tested: the occlusion of the abdominal aorta (ischemia) and spine mechanical compression. The results clearly demonstrated the link between the level of ischemia and the viability state of the spinal tissue. When SCBF decreased, in both experimental models, mitochondrial NADH was elevated, while reperfusion was associated with NADH oxidation. Nevertheless, during the recovery phase, even though SCBF significantly increased (became hyperemic), no further oxidation of NADH was observed. The monitoring of the mitochondrial function together with SCBF by the TVMS reflects the viability of the spinal cord tissue and, together with the conventional monitoring techniques, may help to evaluate the spine conditions, especially under surgical procedures involving the deterioration of the spinal cord blood supply.