Neurally mediated hypotension, also known as the fainting reflex, is low blood pressure that happens because signals between the brain and the heart have somehow become faulty. Signals between the two systems must be synchronized in order for the body to make the necessary adjustments to keep blood pressure within the normal range. Both the brain and the heart are structurally normal in neutrally mediated hypotension, but the reflexive signals between the two are defective regarding the regulation of blood pressure. In response to blood pressure being too low, the nerves in the left ventricle of the heart actually signal the brain that it is too high. When the brain responds by lessening the heart rate to decrease blood pressure, blood pressure then drops too low.
After blood pressure is depressed and drops out of the normal range, an individual might experience symptoms of hypotension, or low blood pressure. Common symptoms of neurally mediated hypotension are repeated episodes of fainting and lightheadedness. Not all individuals will faint; some might have headaches, muscles aches or just feel mentally confused. Extended fatigue after a fairly low level of exertion is one of the more common neurally mediated hypotension symptoms. This type of fatigue can last for as long as 72 hours and get in the way of accomplishing daily activities.
According to medical researchers, the causes of neurally mediated hypotension aren’t well understood. What is known is that certain circumstances or settings seem to be more conducive than others in bringing about symptoms in individuals who are susceptible. In susceptible people, being in a prolonged upright position — such as standing in a line, taking a shower or sitting up straight — can cause this type of hypotension. Neurally mediated hypotension also might happen after one is in an overly warm environment, such as a hot summer day, an overheated room or even a hot bath. In addition to exercising, emotionally stressful events that cause anxiety or fright can contribute to experiencing symptoms.
If symptoms are experienced, it is advisable for the person to consult a doctor as treatment is possible. Neurally mediated hypotension treatment most often involves a combination of blood pressure medication along with increased salt and water intake. Increasing water and salt intake causes the body to retain more fluid and helps keep blood pressure from dropping. As a practical matter, among other postures or physical maneuvers that might be tried, standing with crossed legs and leaning forward when sitting with one's hands on the knees might also help avoid symptoms.