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

Abstract

We hypothesize upright cognitive impairment in Postural Tachycardia Syndrome is due to reduced cerebral blood flow. Cerebral blood flow velocity measured by transcranial Doppler ultrasound decreased excessively during 70° tilt in a minority of patients with intermittent hyperpnea/hypocapnia. Incremental tilt showed no difference in mean cerebral blood flow velocity. But, N-Back memory tasking indicated progressive compromised memory, reduced functional hyperemia and reduced neurovascular coupling. Orthostasis caused slow oscillations in cerebral blood flow velocity linked to oscillations in arterial pressure in Postural Tachycardia Syndrome. We also hypothesize that oscillatory cerebral blood flow velocity degrades neurovascular coupling. We performed 2-Back testing supine and during incremental tilts to 15°, 30°, 45° and 60° in 11 Postural Tachycardia Syndrome and 9 controls. Oscillatory arterial pressure, oscillatory cerebral blood flow velocity and neurovascular coupling were similar supine. Oscillatory arterial pressure increased 31, 45, 67, and 93% in Postural Tachycardia Syndrome during tilt, remaining unchanged in control. Oscillatory cerebral blood flow velocity increased by 61, 82, 161, and 264% in Postural Tachycardia Syndrome during tilt remaining unchanged in control. Functional hyperemia decreased from 4.1% to 3.0, 1.1, 0.2, to 0.04% in Postural Tachycardia Syndrome but was unchanged at 4% in control. Percent correct N-Back responses decreased from 78% to 33% in Postural Tachycardia Syndrome while remaining at 89% in controls. In Postural Tachycardia Syndrome, oscillatory cerebral blood flow velocity was linearly correlated with functional hyperemia (r2=0.76). Increased oscillatory cerebral blood flow is associated with reduced neurovascular coupling and diminished cognitive performance in Postural Tachycardia Syndrome.

Intracranial compliance is associated with symptoms of orthostatic intolerance in chronic fatigue syndrome

“…However, studies using transcranial Doppler ultrasonography showed that patients with POTS and healthy controls have near identical blood flow velocities in the middle cerebral artery, which decreased equally with increasing levels of tilt [ 36 , 37 ]. Instead, POTS patients showed an increase in low-frequency oscillatory blood flow with increasing levels of tilt, whereas controls did not.…”

“…Instead, POTS patients showed an increase in low-frequency oscillatory blood flow with increasing levels of tilt, whereas controls did not. The authors argued that these increased low-frequency oscillations are an expression of impaired cerebral autoregulation and that they might interfere with normal neurovascular coupling [ 37 ]. Low ICC in our high-OI patients may have put a limit on their ability for dynamic cerebral autoregulation, thereby resulting in similar low-frequency blood flow oscillations.…”

Decreasing cerebral oxygen consumption during upright tilt in vasovagal syncope

“…Further study attributed loss of NVC in POTS to oscillatory cerebral blood flow rather than a decrease in mean CBF (Stewart et al. , ). Disruption of NVC has been shown in diabetes, depression, hypertension, stroke, and Alzheimer's disease.…”

Brain fog in postural tachycardia syndrome: An objective cerebral blood flow and neurocognitive analysis

“…Cognitive difficulty, often described as “brain fog”, is a prevalent complaint among patients with POTS 6 . Interestingly, brain fog has been reported to occur even in the supine position and may not be limited to upright posture 7 . Others have demonstrated an approximately 25% increase in cerebral blood flow (CBF) velocity in the posterior cerebral artery (PCA) of healthy individuals in response to visual stimuli 8 .…”