Delivering Blood Flow to the Brain
What Happens to the Brain
The Problem with Gravity
The main issue for people with dysautonomia is that when they stand up, gravity makes it hard for their body to pump enough blood up to their brain. Even if their heart rate speeds up, it's not enough to compensate for the drop in blood flow. This is a critical problem because the brain is an energy-hungry organ that needs a steady supply of blood to function properly.​
As the body is trying to deliver blood "up against gravity," it's important to know that the carotid arteries supply about 80% and the vertebral arteries supply about 20% of the blood flow to the brain. For people with orthostatic intolerance (OI), a term that encompasses a broader group of people than just those with POTS, the blood flow to the brain is not well maintained. This can lead to symptoms even with only mild changes in blood pressure.
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Why is This Not Tested?
While measuring blood flow to the head is a much better way to objectively track dysautonomia symptoms, it is not often tested. This is because the technology has traditionally been high-cost, not portable, and required a specialized technician. These factors can limit its availability and make consistent monitoring difficult. Because of these challenges, many people with dysautonomia have been told their symptoms are normal or that they are fine because their heart rate and blood pressure look good.
What Happens to the Brain
When blood flow to the brain is reduced, a condition called hypoperfusion, it is the root cause of many common dysautonomia symptoms, including lightheadedness, fatigue, brain fog, and nausea.
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Research shows that for people with conditions like POTS or other forms of dysautonomia:
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Brain blood flow decreases significantly when standing, much more than it does in healthy people.
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The drop in brain blood flow happens first, before the heart rate even speeds up (tachycardia).
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The reduced blood flow to the brain directly correlates with symptoms.
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The "brain fog" you feel is a real symptom caused by your brain having to work harder and use more energy to complete a task, leading to greater activation in certain areas of the brain.
The Bigger Picture
A key takeaway is that many people with dysautonomia may have normal heart rate and blood pressure readings but still have abnormal blood flow to the brain. This shows that the traditional ways of testing for these conditions may not be telling the whole story.