Altered cerebrovascular response to breath holding in thoracolumbar spinal cord injury measured using functional near-infrared spectroscopy

Spinal cord injury (SCI) is associated with cardiovascular deficits that affect cerebral blood flow, cerebral perfusion, and cerebrovascular control. While several studies use neuroimaging techniques such as functional magnetic resonance imaging (fMRI) to understand neuroplasticity following SCI, more work needs to be done to evaluate the cerebrovascular changes following SCI. Understanding these effects using neuroimaging is essential as these deficits also affect neurovascular coupling and how we interpret neuroplasticity measured based on neuroimaging. Hence, we conducted a pilot study in twelve healthy males and thirteen males with thoracolumbar SCI using functional near-infrared spectroscopy (fNIRS) to understand the effects of breath-holding induced hypercapnia on the hemodynamics of the sensorimotor cortex and prefrontal cortex (PFC) after SCI. Participants performed 30 seconds of regular breathing alternated by 15 seconds of breath-holding for 5 minutes. Compared to controls, the SCI group presented with a greater initial decrease in oxy-hemoglobin concentration change and a delayed subsequent increase in oxy-hemoglobin concentration change in response to hypercapnia at p<. Additionally, the net increase in oxy-hemoglobin concentration change following BH in the PFC was negatively correlated with the level of injury at p=0.005, where higher levels of injury were associated with a smaller increase in oxy-hemoglobin concentration following hypercapnia. These findings confirm that a) SCI, including lower levels of injury (below T6) are associated with cerebrovascular changes that are quantifiable using fNIRS, and b) fNIRS could be a robust tool to understand the neuroplastic and cerebrovascular changes in people with SCI.