Insights From Bone and Muscle Oxygenation Toward a More Comprehensive Model of Tissue Healing

Introduction

Predicting healing after amputation and revascularization in diabetes and PAD patients with tissue loss is challenging. Current methods, like transcutaneous oximetry, only measure skin oxygenation, overlooking deeper tissues critical for wound healing. Near-infrared spectroscopy (NIRS) during postocclusive reactive hyperemia (PORH) measures muscle oxygenation under ischemic stress but does not account for bone, which is crucial in healing of complex wounds. This study employed NIRS during PORH to evaluate both bone and muscle perfusion in a swine model of hindlimb ischemia.

Methods

Eight Ossabaw swine underwent right hindlimb ischemia induction via endovascular coil occlusion of the right external iliac, femoral, and popliteal arteries. PORH was performed before (T0) and 4 wk after ischemia induction (T4) using a 5-min infrarenal aortic occlusion, with NIRS recording oximetry changes in bilateral gastrocnemius muscle and metatarsal bones. Data endpoints were derived in MATLAB.

Results

At T0 (normal circulation), bone showed a smaller StO₂ drop (P = 0.008), slower oxygen decline (P = 0.050), and smaller oxygen deficit (P = 0.027) during occlusion, along with slower recovery (P < 0.001) during PORH reperfusion. At T4, ischemic bone and muscle had reduced oximetry drops, smaller oxygen deficits, and slower recovery relative to nonischemic tissues. Notably, ischemic bone maintained occlusion rates but had diminished hyperemia response (P = 0.038), differing from muscle dynamics.

Conclusions

Bone and muscle display distinct oxygenation dynamics under ischemia. Chronic ischemia attenuates metabolic and reperfusion responses in both tissues. These findings highlight bone's under-recognized role in ischemia/reperfusion events and the need for comprehensive tissue-specific oxygenation models to predict healing outcomes.