Autonomic dysfunction is common after spinal cord injury (SCI). There are currently limited tools to comprehensively characterize its deficits. While individual established autonomic tests have a long history and sound scientific background, translating these autonomic testing results to inform clinical understanding is a major barrier.
To assess a strategic battery of autonomic tests to characterize and act as a biomarker of autonomic regulation for individuals with SCI and to develop a novel graphical representation of these data to facilitate understanding of autonomic dysfunction after SCI.
We outline a battery of six laboratory autonomic tests that were curated to collectively describe the ability of individuals with SCI to inhibit and recruit sympathetic activity through the injured spinal cord. Heart rate/blood pressure variability, bolus phenylephrine, hand and foot cold pressor, Valsalva maneuver, and bladder pressor are herein described. Incorporating normative control data for 30 uninjured individuals completing this testing battery, we further demonstrate the utility of a composite biomarker, comparing these control results to 11 individuals with SCI.
Results demonstrate strong normality of data with testing psychometrics, suggesting stable reproducibility with repeat testing. Even in this preliminary sample of individuals with SCI, clear differences begin to emerge compared to uninjured norms. This illustrates the ability of this collective testing battery to characterize autonomic regulation after SCI. To aid in clinical translation, we further present a graphical representation, an autonomic phenotype, which serves as a snapshot of how normal or abnormal sympathetic inhibition and recruitment of activation may be after SCI.
Utilizing these autonomic phenotypes, three example cases of individuals with SCI highlight evidence of varied degrees of autonomically complete SCI. Together, this represents a key advancement in our understanding of autonomic function after SCI.
