Abstract P235: Relationship Between Skin Sympathetic Nerve Activity And Nocturnal Non-dipping Blood Pressure In Patients With Postural Orthostatic Tachycardia Syndrome

Background: Patients with postural orthostatic tachycardia syndrome (POTS) have a high incidence of nocturnal non-dipping of blood pressure (BP). Objective: To test the hypothesis that non-dipping of BP is associated with persistently elevated nocturnal skin sympathetic nerve activity (SKNA) in patients with POTS. Methods: We used Bittium Faros 180 ECG monitor to simultaneously record electrocardiogram (ECG) and SKNA, and SpaceLab OnTrak arterial BP monitor (ABPM) over 24-hr in 55 POTS patients (51 women, 36±10 years-old). The Faros signals were high pass filtered at 300 Hz to display the SKNA. The same original signals were bandpass filtered 0.05-150 Hz to display ECG. BP was measured every 30-min when awake (7 AM to 9 PM) and hourly at night (9 PM to 7 AM). Results: The overall successful ABPM measurement was 71±18%. Nocturnal dipping of BP was presented in 40 patients with an average dipping% of 15.5±4.8%. Nocturnal non-dipping of BP was present in 15 patients with an average dipping% of 3.9±3.7% (p<0.001). Figure A shows hourly averaged SKNA. A mixed effect model was used to compare the log (SKNA) values of two groups of patients at all time points, with patient as a random effect. The non-dipping group had higher SKNA from midnight of day 1 to 4 am of day 2 (indicated by the red bars, p=0.0118, 0.0223, 0.0402, 0.0382, 0.0424). The difference between awake time and sleep time (determined by patients’ diary) average SKNA was 0.155±0.106 μV in dipping group and 0.076± 0.101 μV in the non-dipping group (p=0.017, Figure B ). Conclusion: Nocturnal non-dipping of BP is associated with non-dipping of SKNA in patients with POTS suggesting sympathetic nerve activity plays an important mechanistic role.