Abstract 052: Central Gain For Sympathetic Outflow Is Increased In Postural Tachycardia Syndrome

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White noise perturbations using neck suction (NS) can be applied to identify open loop transfer function in a closed loop baroreflex system. It allows an estimation of central arc transfer function (H1) which represents how afferent baroreceptor information is translated into sympathetic outflow and peripheral arc transfer function (H2) which describes how muscle sympathetic nerve activity (MSNA) affects blood pressure (BP). We hypothesize that patients with postural tachycardia syndrome (POTS) have elevated central gain compared to healthy controls (CONT). We recorded raw MSNA and continuous finger BP during randomized NS (0 to -50 mmHg, 0.03-0.3 Hz) and controlled breathing at 0.25 Hz for 6 minutes in 10 female POTS and 9 female CONT. Both groups were matched for age (28.4±2.1 vs. 31.9±3.0 p=0.80) and BMI (23.0±0.7 vs 24.5±1.0, p=0.25). We derived the continuous spike rate using wavelet-based denoising. We estimated median central gain in H1 and peripheral gain in H2 for low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.4 Hz) frequency ranges (Figure). We found that POTS have significantly higher central gain in LF range (2.44±0.38 vs 1.53±0.24 spikes/s/mmHg, p=0.028, MN±SE) but not in HF range (9.02±3.02 vs. 5.06±0.52 spikes/s/mmHg, p=0.604). Median peripheral gains were comparable in LF (0.68±0.15 vs 0.58±0.09 mmHg/spikes/s, p>0.99) and HF ranges (0.18±0.02 vs 0.21±0.03 mmHg/spikes/s, p=0.497). Our results indicate that POTS have higher recruitment of neural sympathetic spike activity during BP oscillations in the LF range. This could explain why higher sympathetic activation/modulation and greater BP fluctuations in the LF range are found during upright in POTS.

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