Introduction
Dysautonomia is a broad term used to describe disorders that affect the autonomic nervous system (ANS). The word "Autonomic" comes from the Latin root meaning "Self-Governing." The ANS works like your brain's "autopilot," since it controls all of the inner workings of our bodies like blood pressure, heart rate, bowel activity, bladder function, and even sweating. When this part of the brain does not function properly, people may develop symptoms such as dizziness, fainting, rapid heart rate when standing, fatigue, digestive problems, or abnormal sweating. Dysautonomia, or dysfunction of the autonomic nervous system, comes in different forms. Each of these are presented in this section. You can click on the menu item to the left to read about each one in particular, or just keep reading below. Keep in mind that there is some overlap in the conditions, and not everyone fits neatly into one particular disorder.
Normal Autonomic System Function
Our bodies consist of many organ systems that function independently, but most of them are controlled to a great degree by the central nervous system. The central nervous system consists of our brain and our spinal cord, which extends down the spine within a bony canal that protects the delicate nerve fibers. Our brain structure is very complicated, and it is unlikely that we will ever understand it completely. We do know that various parts of the brain control different parts of our body. For example, the area in the front is where our thoughts seem to come from, many of our emotions arise from parts of the brain that lie deep within, and the bottom-most part of the brain, called the “brainstem,” is where most of the autonomic control circuits are located. This area of the brain controls things like body temperature, heart rate, blood pressure, sweating, and other internal functions that are beyond our control. That is why this part of the nervous system used to be called the “involuntary” nervous system, meaning we have little or no control over it. On the other hand, the “voluntary” nervous system refers to the brain centers that we use to control muscles like our arms and legs, language, and so on.
The autonomic nervous system is quite complex. It works primarily by reflexes, which are automatic responses to changes in our internal or external environment. When the ANS senses a change, it will often respond by activating one of two functional branches, which can either help us react to stress (physical or emotional) or help our body relax (in a physiologic sense). The first branch, known as the “Sympathetic” nervous system, consists of nerves that travel down the spinal cord, make connections with a network of "ganglionic plexi" located inside the chest wall, and then branch out to control every organ system in the body. When these nerves fire, they release a substance called "adrenaline," also known as "epinephrine," and the result is often referred to as the “fight or flight” reflex, because it causes the heart to speed up, increases the blood pressure, causes sweating, slows down stomach and intestinal activity, and enlarges or dilates the pupils in our eyes. All of these responses are designed to help us deal with a stressful situation.
The second branch of the autonomic nervous system is called the “Parasympathetic” nervous system, and it has the opposite effect of the sympathetic nervous system. The parasympathetic nervous system consists of nerve fibers that arise from the vagus (pronounced “VAY-giss”) nerve, which comes directly off of the brain. When the vagus nerve fires, those nerve endings release a different substance called "acetylcholine," which causes the heart to slow down, the blood pressure to decrease, and the stomach and intestine start pushing the food along more rapidly. The parasympathetic nervous system fires when it's time to "chill out," relax and digest our food. The sympathetic and parasympathetic nervous system balance each other out – like yin and yang – though in most circumstances one predominates over the other (depending on the body’s needs).
The term “dysautonomia” refers to any kind of disorder of the autonomic nervous system. Depending on which part of the autonomic nervous system is affected, symptoms can include dizziness, palpitations, fainting, fatigue, exercise intolerance, digestive problems, or abnormal sweating. It may be brief and self-limited, like a vasovagal faint, also known as "reflex" or Neurocardiogenic Syncope. Vasovagal fainting is a dramatic example of dysautonomia, where certain (usually stressful) circumstances will cause the blood pressure and/or the heart rate to drop suddenly, resulting in a decrease in blood flow to the brain. This results in a temporary loss of consciousness (fainting). A more subtle example of dysautonomia is POTS, or the Postural Tachycardia Syndrome, which is a common syndrome that mostly affects young women. A less common disorder of blood pressure control is known as Orthostatic Hypotension, which is when the blood pressure falls excessively when a person stands up, and is fully discussed later in this section. Finally, more serious causes of progressive autonomic dysfunction are covered in the section on Autonomic Failure.