Changes in spinal cord hemodynamics reflect modulation of spinal network with different parameters of epidural stimulation

Abstract 
In this study functional ultrasound (fUS) imaging has been implemented to explore the local hemodynamic response induced by electrical epidural stimulation and to study real-time in vivo functional changes of the spinal cord, taking advantage of the superior spatiotemporal resolution provided by fUS. By quantifying the hemodynamic and electromyographic response features, we tested the hypothesis that the transient hemodynamic response of the spinal cord to electrical epidural stimulation could reflect modulation of the spinal circuitry and accordingly respond to the changes in parameters of electrical stimulation. The results of this study for the first time demonstrate that the hemodynamic response to electrical stimulation could reflect functional organization of the spinal cord. Response in the dorsal areas to epidural stimulation was significantly higher and faster compared to the response in ventral spinal cord. Positive relation between the hemodynamic and the EMG responses was observed at the lower frequencies of epidural stimulation (20 and 40 Hz), which according to our previous findings can facilitate spinal circuitry after spinal cord injury, compared to higher frequencies (200 and 500 Hz). These findings suggest that different mechanisms could be involved in spinal cord hemodynamic changes during different parameters of electrical stimulation and for the first time provide the evidence that functional organization of the spinal cord circuitry could be related to specific organization of spinal cord vasculature and hemodynamic.