Background
Blood vessels transport oxygen-rich blood throughout the body, ensuring proper organ function. The brain, which usually consumes around 20% of the body’s total oxygen supply, relies on a stable blood flow for optimal performance.
Cerebral (brain) blood flow (CBF) is regulated by the autonomic nervous system, which also controls cardiac (heart) output – the volume of blood the heart pumps per minute. Cardiac output is crucial because it plays a major role in determining how much blood – and therefore oxygen – is available to the brain and other organs.
When a healthy individual stands up, gravity pulls blood toward the lower body, but the body quickly compensates to maintain adequate blood supply to the brain. However, in many individuals with ME/CFS, this compensatory response is impaired, leading to reduced cerebral blood flow and orthostatic intolerance (symptoms – such as dizziness and weakness – when assuming an upright posture).
Research Review
A recent review by a team of researchers and doctors examined different forms of orthostatic intolerance and the CBF abnormalities contributing to orthostatic intolerance in ME/CFS and long COVID. The review highlighted that approximately half of patients who meet symptomatic criteria for orthostatic intolerance do not meet the heart rate and blood pressure thresholds required for a diagnosis of postural orthostatic tachycardia syndrome (PoTS; a specific form of orthostatic intolerance marked by a persistent heart rate increase). Without assessing CBF during PoTS testing, these patients may be deemed “objectively normal,” increasing the risk of their symptoms being misattributed to psychological causes.
The researchers emphasise that cerebral blood flow is a crucial biomarker for orthostatic intolerance. However, they note that standardised CBF monitoring techniques must be established before unified diagnostic criteria can be recommended.
Read about tilt-table testing for orthostatic intolerance in ME/CFS
