Cerebral Blood Flow in Orthostatic Intolerance

Area of Science:

• Neurology
• Cardiology
• Physiology

Background:

• Cerebral blood flow (CBF) is essential for brain oxygen and nutrient supply.
• Orthostatic intolerance (OI) involves impaired upright CBF regulation, causing debilitating symptoms.
• Current diagnostic proxies like heart rate and blood pressure changes are insufficient for many OI syndromes.

Purpose of the Study:

• To review literature on CBF dysfunction in OI syndromes.
• To evaluate methods for measuring CBF in OI patients.
• To highlight orthostatic hypoperfusion as a unifying pathophysiology for OI.

Main Methods:

• Review of existing scientific literature on CBF in OI.
• Evaluation of diagnostic techniques for measuring CBF.
• Analysis of studies involving transcranial Doppler ultrasound, extracranial cerebral blood flow ultrasound, near-infrared spectroscopy, and wearable devices.

Main Results:

• Many OI syndromes, including myalgic encephalomyelitis/chronic fatigue syndrome and long COVID, exhibit normal heart rate and blood pressure despite significant CBF drops.
• Reliance on heart rate and blood pressure can lead to misdiagnosis and lack of treatment.
• Orthostatic hypoperfusion is identified as a common underlying issue across diverse OI conditions.

Conclusions:

• Direct measurement of CBF is necessary for accurate OI diagnosis.
• Standard hemodynamic measures are inadequate for identifying CBF abnormalities in certain OI conditions.
• Accurate CBF assessment is vital for understanding and treating the full spectrum of OI.