Depth profiles of the peripheral blood oxygenation in diabetics and healthy subjects in response to auricular electrical stimulation: Auricular vagus nerve stimulation as a potential treatment for chronic wounds

Chronic incurable wounds comprise a severe problem in diabetics. Their healing is impaired by chronically imbalanced sympathovagal activity of the autonomous nervous system, leading to adverse immune response and reduced microcirculation in the periphery. A targeted modulation of the vagal activity can be reached by percutaneous electrical stimulation of the auricular vagus nerve. The present study reveals novel modulating effects of this stimulation on depth profiles of the peripheral blood oxygenation in diabetics and healthy subjects (for comparison), as objective markers related to wound healing. Applied optical sensors on the sole of foot and the big toe have revealed capillary-venous blood oxygenation profiles close to the skin surface (average depth 2mm), in deep tissues below the surface (8mm), and the average arterial oxygenation (in the toe), as well as the corresponding changes of these profiles in response to the vagus stimulation. In healthy subjects, the stimulation-related profiles have indicated their dependence on the foot skin temperature, whereas in diabetics the oxygenation in deep tissues has tended to increase during the stimulation. The results provide fundamental data on the depth-dependent peripheral effects of the auricular vagus stimulation, as being vitally important for an effective treatment of chronic diabetic wounds.