Abstract

Background: Postural orthostatic tachycardia syndrome (POTS) diagnosis often takes over five years from symptom onset. While heart rate change upon standing is a useful diagnostic indicator, POTS's diverse nature complicates management. Amplitude fluctuations in blood pressure (BP) within this condition have been underexplored. We propose a new marker based on the systolic blood pressure range (SBPR) in a 30-second fixed time window to improve POTS characterization. Methods: We collected data from 10 healthy controls and 10 POTS patients (all female), recording beat-to-beat BP during a 10-minute supine baseline and a 10-minute Head-Up Tilt (HUT) test at 80°. SBPR was calculated within a 30-second window to cover the observed SBP fluctuations. Hemodynamic contributions to SBPR were determined by constructing a log-linear mixed-effects univariate model. The Mann-Whitney U and Wilcoxon rank-sum tests assessed inter- and intra-group differences. Median data are reported. A significance level of p <0.05 was chosen. Results: Participants had a median age of 27 years and a median BMI of 24 kg/m2, without significant differences between groups. Both groups showed a significant decrease in the SBP fluctuation period from supine to HUT (Controls: 17.9 s vs. 11.5 s; p=0.014; POTS: 25.0 s vs. 12.2 s; p=0. 006), but no significant differences were found between groups in either position. SBPR was therefore calculated within a 30-second window to cover the observed SBP fluctuations. POTS patients had higher SBPR values than controls while supine (13.9 mmHg vs. 10.3 mmHg; p=0.038) and during HUT (21.0 vs. 14.2 mmHg; p=0.038). The univariate model for the POTS group showed an association between reduced stroke volume and increased SBPR (βSV= -0.013, p= 0.0003), but this association was not present in controls. Conclusion: Patients with POTS show increased SBPR compared to healthy controls, both while supine and during HUT. Increased SBPR is related to a decreased SV in POTS, potentially indicating the difficulty of the cardiovascular system in adjusting to this drop. Elevated SBPR is a novel hemodynamic marker in POTS and should be studied for its potential to improve diagnostic accuracy.