Orthostatic hypoperfusion is a shared pathophysiology across forms of orthostatic intolerance, highlighting the need to directly measure cerebral blood flow rather than relying on heart rate or blood pressure proxies.
How can cerebral blood flow be accurately measured to diagnose orthostatic hypoperfusion in patients with orthostatic intolerance?
Highlights the critical need to directly measure cerebral blood flow in orthostatic intolerance syndromes, as traditional proxies like heart rate and blood pressure may fail to detect underlying hypoperfusion.
Cerebral blood flow (CBF) is vital for delivering oxygen and nutrients to the brain. Many forms of orthostatic intolerance (OI) involve impaired regulation of CBF in the upright posture, which results in disabling symptoms that decrease quality of life. Because CBF is not easy to measure, rises in heart rate or drops in blood pressure are used as proxies for abnormal CBF. These result in diagnoses such as postural orthostatic tachycardia syndrome and orthostatic hypotension. However, in many other OI syndromes such as myalgic encephalomyelitis/chronic fatigue syndrome and long COVID, heart rate and blood pressure are frequently normal despite significant drops in CBF. This often leads to the incorrect conclusion that there is nothing hemodynamically abnormal in these patients and thus no explanation or treatment is needed. There is a need to measure CBF, as orthostatic hypoperfusion is the shared pathophysiology for all forms of OI. In this review, we examine the literature studying CBF dysfunction in various syndromes with OI and evaluate methods of measuring CBF including transcranial Doppler ultrasound, extracranial cerebral blood flow ultrasound, near infrared spectroscopy, and wearable devices.
Khan et al. (Mon,) conducted a review in Orthostatic intolerance. Methods of measuring cerebral blood flow was evaluated. Orthostatic hypoperfusion is a shared pathophysiology across forms of orthostatic intolerance, highlighting the need to directly measure cerebral blood flow rather than relying on heart rate or blood pressure proxies.