Comparisons of Evoked Skin Vasomotor and Sudomotor Responses to Single Pulse Median Nerve Stimulation
Authors: Mylavarapu Ramanamurthy , Albuquerque Eric , Farkas Gary , McMillan David , Ganzer Patrick 
Published: May 2024

The sensorimotor dysfunction caused by cervical and thoracic spinal cord injury (SCI) is concomitant with sympathetic nervous system dysfunction, evidenced by the high prevalence of orthostatic hypotension and autonomic dysreflexia. Although the International Standards for Neurological Classification of SCI evaluate sensorimotor function both above and below the injury level, there are limited quantitative measures for gauging sympathetic outflow and the extent of dysautonomia resulting from neurological damage. Despite studies on the effects of SCI on electrodermal activity (EDA) and blood pressure (BP), there is a lack of detailed feature comparisons involving EDA, skin vasomotor activity, and BP. Therefore, we investigated the relationship between EDA, skin vasomotor, and BP responses to sympathetic activation via median nerve stimulation in persons with and without SCI. Adults with and without SCI (cohort demographics presented in poster) participated in this study. Lead II electrocardiogram (ECG), pneumogram (P), photoplethysmogram (PPG), and EDA were recorded from either the trunk (ECG, P) or both limbs (PPG, EDA). Beat-by-beat BP was recorded from the middle finger of the left hand (VitalStream, CareTaker Medical). Evoked responses in the above signals were measured surrounding a cathodal electrical pulse (30 mA, 200 μs) delivered to the distal right median nerve 1-2 cm proximal and medial to the radial styloid process either during systole or diastole of the cardiac cycle. There were notable differences between baseline signals before and after the experimental session, along with a consistent reduction of limb temperature (> 2° Celsius). Increases in EDA (greater than two standard deviations from baseline) were found across non-SCI participants following stimulation both during systole and diastole, along with skin vasoconstriction following the onset of EDA modulation (> 50% of trials). Individual differences were noted in evoked responses to stimulation at systole vs. diastole. Furthermore, attenuated responses were observed in individuals with SCI. Stimulation caused no evoked signal response habituation across trials within participants. Additionally, evoked BP changes were not consistent across all individuals with respect to stimulation. Our results show a fixed relationship between evoked skin vasomotor and sudomotor responses to single pulse stimuli across participants and had consistent waveform features. Potential individual effects of stimulation delivered at systole vs. diastole warrant an in-depth analysis of reflex gating of sudomotor and skin vasomotor responses. This would present insight into the population with SCI, where dysfunction could greatly exaggerate reflex gating. 1R01NS131493-01. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.