New Paper: Cerebral Blood Flow Key to Understanding Orthostatic Intolerance

New Paper: Cerebral Blood Flow Key to Understanding Orthostatic Intolerance

Have you ever felt lightheaded when standing up? For millions of people around the world affected by syndromes such as Postural Orthostatic Tachycardia Syndrome (POTS), Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Long COVID, it's not just a passing feeling. It's a debilitating and chronic problem known as Orthostatic Intolerance (OI).

A new review article in the Journal of the American Heart Association, Cerebral Blood Flow in Orthostatic Intolerance, highlights the importance of measuring cerebral blood flow (CBF) in diagnosing and managing this problem.

What is cerebral blood flow and why does it matter? CBF is the blood supply to the brain, delivering vital oxygen and nutrients. In Orthostatic Intolerance, this blood flow may be decreased when a person is upright, leading to a variety of symptoms including lightheadedness, fatigue, brain fog, and even fainting.


The problem is that traditional measures, such as heart rate and blood pressure, don't always tell the whole story. Many people with Orthostatic Intolerance have normal heart rate and blood pressure despite experiencing significant drops in CBF. This means some people are told nothing is wrong, even if they still feel bad.

The figure below, re-published in the JAHA review, shows how CBF can drop in different types of conditions, regardless of what happens to HR and BP:

HR, BP, and CBF velocity patterns in example participants with orthostatic hypotension, orthostatic cerebral hypoperfusion syndrome, and POTS during supine (gray) and head‐up tilt (white) compared with a healthy control on the left. Despite different changes or no change in BP and HR during head‐up tilt, participants with orthostatic intolerance experience a similar and excessive decline in cerebral blood velocity. Charts reproduced from Novak3 under the terms and conditions of the Creative Commons Attribution Non‐Commercial‐NoDerivatives license (https://creativecommons.org/licenses/by‐nc‐nd/4.0/). BP indicates blood pressure; CBF, cerebral blood flow; HR, heart rate; and POTS, postural orthostatic tachycardia syndrome.

This is where the importance of CBF assessment comes in. The review article in JAHA discusses various methods for measuring CBF, including transcranial Doppler ultrasound (TCD), extracranial ultrasound, and even wearable devices, like the technology developed by Lumia Health for proposed, future diagnostic use.

By assessing brain blood flow during postural changes, healthcare providers can gain a more accurate understanding of a patient's condition and tailor treatment accordingly.

Methods for CBF measurement: Ultrasound is used to assess blood flow velocity to the head either at the middle cerebral artery using TCD ultrasound or at the external carotid artery via extracranial ultrasound. NIRS supplies an index of oxygen saturation of the frontal lobe with oximetry by shining near‐infrared light at the forehead. In‐ear pulse‐wave analysis is an emerging technique to remotely measure blood flow to the head using infrared light to the posterior auricular branch of the external carotid artery. CBF indicates cerebral blood flow; NIRS, near‐infrared spectroscopy; and TCD, transcranial Doppler.


This groundbreaking review was authored by prominent experts in autonomic and cardiovascular disorders. Co-first authors Dr. Muhammad Khan (Duke University) and Dr. Amanda Miller from Lebanon Valley College collaborated with Dr. Marat Fudim (Duke University), Dr. Satish Raj (University of Calgary), Dr. Harikrishna Tandri (Vanderbilt University), and many others. 

The implications of this information are far-reaching. Not only does it shed light on the underlying mechanisms of these chronic autonomic disorders, but it also emphasizes the need for better diagnostic tools and treatments. 

By raising awareness of the importance of CBF monitoring or assessment, we can help improve the lives of millions of people living with POTS, Orthostatic Hypotension, Vasovagal Syncope and other forms of Dysautonomia, as well as Long Covid and ME/CFS. 

 

Download the print-friendly PDF of this important new review here.

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