Altered oscillatory cerebral blood flow velocity and autoregulation in postural tachycardia syndrome

Abstract

Decreased upright cerebral blood flow (CBF) with hyperpnea and hypocapnia is seen in a minority of patients with postural tachycardia syndrome (POTS). More often, CBF is not decreased despite upright neurocognitive dysfunction. This may result from time-dependent changes in CBF. We hypothesized that increased oscillations in CBF occurs in POTS (N = 12) compared to healthy controls (N = 9), and tested by measuring CBF velocity (CBFv) by transcranial Doppler ultrasound of the middle cerebral artery, mean arterial pressure (MAP) and related parameters, supine and during 70° upright tilt. Autospectra for mean CBFv and MAP, and transfer function analysis were obtained over the frequency range of 0.0078–0.4 Hz. Upright HR was increased in POTS (125 ± 8 vs. 86 ± 2 bpm), as was diastolic BP (74 ± 3 vs. 65 ± 3 mmHg) compared to control, while peripheral resistance, cardiac output, and mean CBFv increased similarly with tilt. Upright BP variability (BPV), low frequency (LF) power (0.04–0.13 Hz), and peak frequency of BPV were increased in POTS (24.3 ± 4.1, and 18.4 ± 4.1 mmHg2/Hz at 0.091 Hz vs. 11.8 ± 3.3, and 8.8 ± 2 mmHg2/Hz c at 0.071 Hz), as was upright overall CBFv variability, low frequency power and peak frequency of CBFv variability (29.3 ± 4.7, and 22.1 ± 2.7 [cm/s]2/Hz at.092 Hz vs. 14.7 ± 2.6, and 6.7 ± 1.2 [cm/s]2/Hz at 0.077Hz). Autospectra were sharply peaked in POTS. LF phase was decreased in POTS (-14 ± 4 vs. -25 ± 10 degrees) while upright. LF gain was increased (1.51 ± 0.09 vs. 0.86 ± 0.12 [cm/s]/ mmHg) while coherence was increased (0.96 ± 0.01 vs. 0.80 ± 0.04). Increased oscillatory BP in upright POTS patients is closely coupled to oscillatory CBFv over a narrow bandwidth corresponding to the Mayer wave frequency. Therefore combined increased oscillatory BP and increased LF gain markedly increases CBFv oscillations in a narrow bandwidth. This close coupling of CBF to MAP indicates impaired cerebral autoregulation that may underlie upright neurocognitive dysfunction in POTS.

Oscillatory Cerebral Blood Flow Is Associated With Impaired Neurocognition and Functional Hyperemia in Postural Tachycardia Syndrome During Graded Tilt

“…This results from the combined effects of increased OAP in the LF band and increased LF transfer gain from OAP to OCBF in POTS. We have shown greatly increased CBF v in POTS when upright which is protected by an autoregulatory mechanism 18 which comprises properties of the vasculature that, in the absence of large environmental or metabolic changes, maintain CBF relatively unchanged despite changes in BP 25 . While the utility of these oscillations is poorly understood, our data suggest that OCBF interferes with NVC and that altered OCBF might serve as a marker for Brain Fog 8 in POTS.…”

“…We recently observed greatly increased slow CBFv oscillations (<0.40 Hz) in POTS compared to controls during 70° upright tilt 18 suggesting that oscillatory CBF power interferes with cognition and neurovascular coupling. Therefore, we used incremental upright tilt and related increases in OCBF to decreases of functional hyperemia and cognitive performance in POTS, but not in healthy volunteers.…”

Heart rate and heart rate variability comparison between postural orthostatic tachycardia syndrome versus healthy participants; a systematic review and meta-analysis.

“…While other studies matched the groups by age (14,22), other studies did not (24). Furthermore, the majority of studies reported participants' ages central tendencies by mean, two studies utilized median instead (25,26). While other studies used a larger sample size (27), other used smaller sample sizes (28).…”

“…This led to conducting sensitivity analysis excluding this study. Furthermore, the overall mean ages of POTS and/or healthy group could not be calculated because data could not be accessed in other studies (28,32), because the median was utilized than the mean (25,26). Figure 2 illustrates eighteen of twenty eligible studies that compared HR outcomes between POTS versus Healthy participants.…”

Neuro-humoral control during orthostasis in health and disease

“…Patients with POTS have acute changes in cognitive performance in response to orthostatic challenges, and these patients also have an increased prevalence of depression and higher levels of anxiety (Anderson et al, 2014 ). Impaired cerebral autoregulation may underlie upright cognitive dysfunction in POTS (Medow et al, 2014 ).…”