ABSTRACT OF THE DISSERTATION

Explorations of Postural Orthostatic Tachycardia Syndrome With Electrodermal Measures of Sympathetic Function

by

John Oyigoga Akuma OdehDoctor of Philosophy in Nursing University of California, Los Angeles, 2024 Professor Wendie A Robbins, Chair

Background: Autonomic reflex screening (ARS) is central to the diagnosis of dysautonomia. Postural orthostatic tachycardia syndrome (POTS) is a heterogenous disorder involving the autonomic nervous system (ANS) with varying etiology. Electrodermal activity (EDA) is an indicator of sympathetic nervous system activity, however its utility in mechanistic characterization of POTS is unexplored.Aim: To explore characteristics of postural orthostatic tachycardia syndrome (POTS) through analyses of associations, trends, and values among measures of gold standard (or reference) indices of autonomic function tests (AFTs), as well as those of electrodermal activity (EDA) traces, measured concurrently during autonomic reflex screening (ARS) appointments at the University of California, Los Angeles’ (UCLA’s) Cardiac Arrhythmia Center (CAC). Methods: Of 595 patients referred for autonomic testing, 100 patients with head up tilt-table testing (HUTT), and palmar-EDA were included and classified as POTS-cases (n=75) or control subjects (n=25). Beat-to-beat noninvasive blood pressure, heart rate, and symptoms were concurrently assessed at baseline, HUTT, Valsalva maneuver, and deep breathing. Quantitative sudomotor data were collected. Results: Average sample age was 32 ± 16; 28, and 76.0% were female (n=76). Heart rate changes to HUTT in POTS-patients were greater than in controls (54.8 ± 10.4; 52.7 vs. 26.6 ± 7.4; 26.1 bpm, p<0.01). Four tonic-EDA patterns (Transient, Absent, Delayed, and Persistent) reflecting differing sympathetic responses were identified during tilt. The distribution of EDA patterns differed between POTS-cases and controls (p<0.01). Specifically, the EDA pattern most common in control patients (Transient) was seen in a minority of POTS patients, while the EDA pattern indicating persistent sympathetic drive for the duration of upright-tilt was seen in 42.7% of POTS-patients but 0% of controls (p<0.01). The EDA pattern reflecting delayed sympathoexcitation to HUTT was associated with high heart rates and clinical symptoms (100%) (p<0.01) in POTS-patients. Skin conductance responses (SCRs), during deep breathing, Valsalva and upright tilt, exhibited shorter SCR rise in the cases with POTS versus the controls. Similarly, the half-recovery times were shorter in the POTS-cases versus the controls. The raw amplitudes of the event-based SCRs were higher in the POTS-patients than in control-patients. The medians of the Z-score transformed raw amplitudes were lower in the control-patients than in the patients with POTS. In contrast, during deep breathing, the medians of the T-score transformed raw amplitudes were higher in the control-patients than in patients with POTS. The strength of associations ranged from weak to very strong, with strong associations between certain EDA indices and the AFTs of HR difference during deep breathing, indices of vagal response during Valsalva, and the difference between the HR at the minimum SBP during upright tilt and its pre-tilt baseline value. Conclusion: Phasic and Tonic-EDA patterns during upright-tilt, indicate differing mechanisms of POTS and identify highly-symptomatic-patients. Further studies are needed to validate these findings and to explore the utility of understanding EDA differences in patients with POTS. Supplemental Materials: Excel workbooks containing datasets constructed from the patient records appraised in the course of this study, will be uploaded to electronic archives for the interested reader.