The purpose of this research is to learn about how the participant's body is able to balance changes in blood pressure, and how spinal cord stimulation affects these changes as well as immune & cardiovascular function in participants with spinal cord injury.

Inclusion criteria

• Age 18-50.
• American Spinal Injury Association Impairment Scale A-D,64 to encompass a representational spectrum of autonomic dysfunction after spinal cord injury.
• Neurological level of injury, C6-T8, as defined by the International Standards for Neurological Classification of Spinal Cord Injury.64 Incorporating level of injury over this broad range to capture the spectrum of autonomic dysfunction. Individuals with injuries below T8 will not be included to ensure transcutaneous spinal cord stimulation does not occur over the injury/glial scar, where it may have altered properties. The C6 level was chosen to ensure hand cold pressor stimuli triggers above level sympathetic activation.
• Time since injury of greater than six months, given early changes in spinal cord connectivity and recovery prior to this.
• Both individuals with and without currently implanted epidural spinal cord stimulators will be enrolled.
• Twenty uninjured controls will also be enrolled.

Exclusion criteria

• History of clinically diagnosed cardiovascular disease, diabetes, autonomic neuropathies, neurological disorders (with exception of spinal cord injury for individuals in those cohorts), or are active smokers.
• Individuals who are taking betablockers, antihypertensives, or other sympathetically active medications which they are unable to hold.
• Women who are pregnant or lactating, given known hormonal influences on autonomic regulation.65,66
• Cognitive issues preventing informed consent for participation.
• Body mass index >30 kg/m2 for the uninjured controls only given increased risk of prediabetes and potential confounding normative values.
• taking or being administered a medication known to potentially have adverse interactions with phenylephrine
• in the judgement of the principal investigator, any illness or condition that will interfere with the patient's ability to comply with the protocol, compromise patient safety, or interfere with the interpretation of the study results