ASK THE GP: No explanation for two years of blackouts

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My father-in-law, 70, has had fainting episodes for the past two years. When he blacks out, it’s usually twice in two hours with little warning, and he is unconscious for 20 to 30 seconds. He broke his jaw in one of the falls — we are all concerned.

Sara Brindley, Sheffield.

I suspect he is suffering from syncope, fainting caused by a temporary reduction in the flow of blood and oxygen to the brain. It is usually triggered by a sudden drop in blood pressure and resolves itself once the blood flow resumes. However, this doesn’t mean it isn’t dangerous — as his broken jaw attests.

There are other causes of a sudden loss of consciousness, including seizures, intoxication, metabolic disturbances (e.g. low blood sugar) and conversion disorders (psychological conditions). But the fact your father-in-law is in generally good health, yet has suffered these sudden and worrying episodes for two years, leads me to conclude that these are not relevant in his case.

So, the questions remain: what is the cause? And how can these episodes be prevented?

In terms of the cause, there are three main possibilities: neurological syncope, also known as reflex syncope, caused by a glitch in the autonomic nervous system; orthostatic syncope, when the blood pressure drops on standing or when standing in a hot, crowded place; and cardiovascular syncope, which is related to heart problems.

Made up of the brain, nerves and spinal cord, the nervous system regulates heart rate and blood pressure. In those with neurological syncope, something as simple as a laugh or a sneeze can stop the nervous system working properly, resulting in blood pressure falling and the person fainting.

This could be the cause, but I think it is not the most likely.

The low blood pressure of orthostatic syncope is often due to other health conditions, such as diabetes or medication for high blood pressure or depression. In your longer letter, you describe your father-in-law as active and in relatively good health, which makes me suspect this is unlikely to be the cause, either.

Taking into account his age, I think it is most likely a heart problem is intermittently interrupting the blood supply to his brain and causing him to faint. If this is the

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