Medical Matters > Dysautonomia: Orthostatic Intolerance (OI) and Postural Orthostatic Tachycardia Syndrome (PoTS)

ME Essential Summer 2021


I keep reading about orthostatic intolerance, PoTS and postural hypotension and how they can all be symptoms of ME/CFS. But what do all these medical terms mean? What is going wrong? And are all these symptoms and syndromes related to each other?


One of the key parts of the nervous system that is affected by ME/CFS is known as autonomic nervous system (ANS). If this is not functioning correctly it is known as dysautonomia or ANS dysfunction in medical jargon. From control centres in the brain, the ANS sends out messages to the heart, blood vessels, bowel and bladder to basically either speed them up or slow them down through what are known as the sympathetic and parasympathetic nervous systems. In relation to the cardiovascular system, the ANS plays a very important role in altering heart rate and blood pressure when changes take place in posture from lying or sitting to standing.

The ANS is there to make sure that when we move from lying or sitting to standing, there are rapid compensatory mechanisms in place to ensure that on standing up there is still enough blood being pumped to the brain to maintain normal brain activity. When this vital neurological/cardiovascular control system becomes defective people have problems when standing up and/ or maintaining an upright posture. This is known as orthostatic intolerance (OI) and is one of the key diagnostic features of ME/CFS. Unfortunately, many doctors are not aware of this very common and disabling symptom. So it is often badly managed, or not managed at all. If the blood pressure falls too much during a change in posture from lying to standing this is known as orthostatic or postural hypotension.

Both conditions can cause dizziness, light-headedness, blurred vision, mental confusion, nausea and feeling faint, or even fainting. If the pulse rate rises excessively (ie more than 30 beats per minute in adults or 40 beats per minute in adolescents) when moving from lying to standing within 10 minutes of doing, so this is known as postural orthostatic tachycardia syndrome (PoTS). PoTS seems to be more common in younger people with ME/CFS. Finally, it is interesting to note that all these symptoms of ANS dysfunction are being quite commonly reported in people with Long Covid.

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Medical Matters is for information purposes only. The answers provided by Dr Shepherd and the ME Association’s other expert advisers should not be construed as medical advice. We recommend that any information you deem relevant is discussed with your GP as soon as possible. It is important to obtain advice from a GP who is in charge of your clinical care, who knows you well, and who can consider other likely causes for symptoms. Seek personalised medical advice whenever a new symptom arises, or an existing symptom worsens. Don't assume that new or worsened symptoms are a result of having ME/CFS.

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