Orthostatic hypotention (OH) describes a sudden drop in blood pressure as a result of moving from a laying down position to sitting or standing position. This is a persistant happening, not occasional, such as what may happen when you stand up to fast.
Chronic orthostatic intolerance (OI) is the inability to stand for a prolonged period of time due to dizziness, lightheadedness or drops in blood pressure. This term is used with people who have dysautonomias that make them unable to tolerate standing for long, but don’t have persistent or consistent OH.
Neither of these conditions are considered a diagnosis of dysautonomia. They are symptoms of dysautonomias or other health issues.
Orthostatic hypotention can occur when the brain does not activate the symathetic noradrenergic system, which is an involuntary system that sends signals to tighten blood vessels in response to changes in body position. It can also be triggered by a failure of the sympathetic neurocirculatory system to work. The reasons for this disruption can be varied. They include:
Because the body has such a complex system for maintaining blood pressure, there are other factors that can cause orthostatic hypotension. Focus is first put on the symathetic noradrenergic system because it is the main controler for blood pressure. Chronic orthostatic intolerance is a symptom of an underlying disease or diseases, chronic fatigue syndrome, POTS, syncope and dysautonomias that disrupt the symathetic noradrenergic system. There are so many causes for this symptom that doctors have to search for what dysautonomias or other conditions are present to determine the cause in individual cases. It’s important to note that orthostatic hypotension can cause orthostatic intolerance, but doesn’t always. The reverse is also true.
Patients with OH experience:
Patients with OI cannot tolerate standing for long substatial periods of time without experiencing some of the following, most of which cannot be measured by a doctor:
A tilt table is often used in testing for both OH and OI. A patient lays down on and is secured to a table. Their vital signs are monitored while the table is raised so that the patient’s head is above their feet. In addition to producing findings that can result in the diagnosis of POTS or neurocardiogenic syncope, this test also shows if the patient experiences OI, OH or both in conjunction with other symptoms for these specific dysautonomias.
Information on this page comes from Principles of Autonomic Medicine by Dr. David Goldstein, MD PhD