Many of the symptoms experienced in Long Covid are also seen in patients with autonomic dysfunction. Through mechanisms that are still unknown, Covid infection appears to influence the body’s autonomic nervous response in a negative way. One way to think of the autonomic nervous system, is that this is the bit of the brain that controls all the automatic functions, which includes setting the appropriate level for blood pressure, heart rate, peristalsis (or gut movement), sweating, or temperature regulation. Essentially these are all the subconscious activities that take place and are typically very finely automatically regulated in day-to-day life, such that we simply do not have to think about these bodily functions in day-to-day existence.
However, after an infection with Covid, the autonomic nervous system may achieve a different set point. For example, it may cause patients who were previously fit and well within normal blood pressure, to have a slightly low blood pressure, which may be just above the normal range, but which becomes abnormal for that particular patient. Long Covid appears to affect a higher proportion of patients who have previously been extremely fit and well, and even highly athletic (participating in long-distance endurance events) with a healthy cardiovascular profile, relative to other diseases. One potential explanation for this, is with a period of physical deconditioning during the acute Covid illness, the volume of blood reduces and hence the autonomic nervous system set points which control the blood pressure and heart rate become slightly dysregulated. Other theories include the lack of effective vasoconstriction (where vessels, particularly in the lower limbs, are made to squeeze in response to adrenaline, to return blood to the heart), and this lack of adequate blood volume return to the heart triggers the adrenaline reaction that remains high in various states, accounting for some of the symptoms of autonomic dysfunction in Long Covid.