Cerebral Autoregulation is affected in Postural Tachycardia Syndrome

Abstract

Orthostatic intolerance (OI) is defined by symptoms and signs while upright, relieved by recumbency. Included are symptoms of CNS malperfusion. Chronic OI, also known as postural tachycardia syndrome (POTS), is associated with excessive upright tachycardia. We hypothesized that CNS symptoms are due to defects of dynamic and static cerebral autoregulation (CA). Nine normocapnic POTS patients and 6 control subjects, ages 15‐27, were continuously monitored for heart rate (HR), mean blood pressure (MAP), end‐tidal CO2, and cerebral blood flow velocity (CBFV) during a supine period and 70° head‐up tilt. Transfer function analysis, with low frequency (LF) between 0.04‐0.15 Hz and high frequency (HF) between 0.15‐0.40 Hz, compared MAP and CBFV. During tilt, POTS had a higher HR than controls (112 ± 14 vs. 83 ± 9 bpm) and lower systolic BP (110 ± 11 vs. 123 ± 4 mmHg). Supine CBFV decreased during tilt in POTS from 66 ± 21 to 54 ± 15.3 cm/s; whereas, in controls it dropped from 67 ± 16.5 to 61 ± 14.9 cm/s. Analysis during tilt showed that POTS exhibited a higher LF and HF coherence than controls (LF: 0.85 ± 0.11 vs. 0.30 ± 0.09; HF: 0.81 ± 0.16 vs. 0.24 ± 0.09). The greater decrease of CBFV during tilt in POTS compared to controls shows decreased static CA affecting CNS perfusion. The high coherence between MAP and CBFV in POTS implies decreased dynamic CA, which permits BP oscillations to further compromise phasic CBF.