Measuring cerebral bloow flow with Transcranial Doppler while performing a high-intensity cognitive task (without pauses) while sitting seems like it might be a useful test. I believe it would show that blood flow continues to decline with exertion as the brain becomes fatigued and metabolism declines. As far as I know this specific test hasn't been done yet, but there was a study that did repeated cognitive testing during PEM, which found a decline in performance over time. Transcranial Doppler has already been used in ME/CFS to show a decline in cerebral blood flow in severely ill patients undergoing some orthostatic stress (I can't recall the details at the moment).
@Hoopoe Are you thinking of these studies with transcranial doppler and ME? https://www.sciencedirect.com/science/article/pii/S2467981X20300044 https://www.mdpi.com/2227-9032/8/4/394 [I am certain I put the links in the first time but when I came back they weren't there.... Ah well... I hope they stay put now.]
Yes I was thinking about that study. They used tilt tests to provoke reduced cerebral blood flow, and in another study severely ill patients showed reduced cerebral blood flow just by sitting up, if I recall correctly. If we could provoke and document reduced cerebral blood flow by having patients do a cognitively demanding task while wearing a Transcranial Doppler headband we would have a widely usable diagnostic test for at least that aspect of ME/CFS. The cognitively demanding task could be just a cognitive test in front of a PC. Assuming that a cognitive test actually results in CBF abnormalities (in comparison to healthy people). I suspect it does.
A few potentially relevant references from a quick search — Transcranial Doppler ultrasound in vascular cognitive impairment-no dementia (2019, PLOS ONE) Cognitive tasks and cerebral blood flow through anterior cerebral arteries: a study via functional transcranial Doppler ultrasound recordings (2016, BMC Medical Imaging) The assessment of neurovascular coupling with the Addenbrooke’s Cognitive Examination: a functional transcranial Doppler ultrasonographic study (2018, Journal of Neurophysiology) Psychopathological Symptom Load and Distinguishable Cerebral Blood Flow Velocity Patterns in Patients With Schizophrenia and Healthy Controls: A Functional Transcranial Doppler Study (2021, Frontiers in Psychiatry)
@Hoopoe , I'm only new today, but happened to see this thread. I think a similar study to what you are thinking of has been done on POTS patients in 2020: "Cerebral Blood Flow and Cognitive Performance in Postural Tachycardia Syndrome: Insights from Sustained Cognitive Stress Test" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7955388/
Thread here: Cerebral Blood Flow and Cognitive Performance in Postural Tachycardia Syndrome: Insights from Sustained Cognitive Stress Test, Wells et al, 2020
