Orthostatic hypotension, the presence of inadequate blood pressure when one assumes the standing position after being seated or recumbent, is more common than generally assumed. The time devoted to this in medical school is negligible when one considers how frequently this is encountered in medical practice.
Only in my USAF flight surgeon training days did we young military doctors really get into the physiology of all this as we experienced special testing such as in the centrifuge or tilt table.
You expect poor blood supply to the brain in the centrifuge whirling about at 7 G's. After all, in that situation your blood weighs seven times normal, well beyond your heart's capacity to pump it to your brain.
We were studying the rigors of the flight environment then, defining man's limits and developing countermeasures. More commonly we were evaluating the occurrence of fainting in a flight crew member, requiring tilt table testing as part of the work-up.
In this simple procedure our patient was strapped securely to a platform equipped with a foot-rest. After the baseline measurements were taken the platform was tilted upright and continuous blood pressures, heart rate (and even electrocardiograms upon occasion) were recorded.
More often than not these fainting cases turned out to be vagal in origin, a simple faint due to transitory loss of vascular reflexes. Often these were associated with mild illness or gross excesses the night before while partying and although orthostatic intolerance by definition (blood pressure inadequate for the upright posture) were innocent and transient in nature.
The orthostatic intolerance of concern in this article represents a permanent loss of effectiveness of those autonomic (automatic) vascular reflexes whose job it is to insure adequate blood flow to the brain. Because my military research was focused on the debility of prolonged exposure to zero gravity I suspected we could anticipate loss of these vascular reflexes. The stimulus to maintain these reflexes is gravitational change and in zero gravity this important factor would be absent.
Using bed rest and water immersion testing, both very helpful analogues of the zero gravity state, I quickly proved my suspicions that vascular reflexes would be the first to go. The tilt table became my most important testing device. In subject after subject after prolonged bed rest or immersion the subject would show the typical loss of blood pressure and heart rate on raising the tilt table with fainting inevitable if the table was not promptly lowered.
This was orthostatic hypotension and although there can be other causes such as profound anemia, or exposure to certain drugs the most common cause is loss of these protective vascular reflexes. The autonomic nervous system is compromised; the vascular reflexes no longer work adequately.
It is quite rare in clinical practice to test for this condition unless there is a clear history of fainting but the symptoms can be quite varied. There can be profound weakness or unusual sweating or loss of balance associated with standing upright. There can be nausea and even vomiting.
More importantly there can be compromise of cognitive function. Memory can vanish with a dullness of personality and loss of affect. Often these symptoms can falsely point to dementia unless the unfortunate patient has the good luck to faint, thereby putting the doctor on the right diagnostic track. The patient's history may be helpful, for example if surgery has been done involving the lumbosacral area one has to consider that the blood pressure control part of the autonomic nervous system is located there and a history of back surgery in that location is common.
Accidents can cause fractures of the pelvis that may contribute. Pelvic surgery and radiation to the pelvic area are common and all of these can be possible contributors to autonomic dysfunction. Certain drugs also can predispose to autonomic dysfunction.
Strange as it may seem, hypertension may co-exist with orthostatic hypotension and, surprisingly, someone with a sitting blood pressure of 200/100 may drop to 135/95 on standing. Most of the time a hypertensive will be on anti-hypertensive therapy leading to a diagnosis of drug overdose and causing considerable juggling of medicines before proper treatment is finally established.
Most doctors will do an orthostatic evaluation in their offices simply by comparing the standing blood pressure with sitting and recumbent values. Most authorities agree that a 20/10 decrease in standing blood pressure (that is a 20 mm Hg fall in systolic or 10 mm Hg fall in diastolic) as diagnostic. Although a tilt table test can easily be done, in my judgment it is probably not necessary to establish this diagnosis.
Once the diagnosis has been established the usual case will respond to increasing salt intake, the use of high quality support hose to the lower legs and the routine use of a snug lumber belt. Also they will be instructed to do things such as sitting for a few seconds after a period of lying down before standing upright and make sure of stability in the upright position before walking.
For resistant cases, information on anti-G suits is available at: www.OIResource.com.
Military versions are heavy and designed for rigorous use. One can quite easily convert to a lightweight, far more comfortable, civilian version. Email me for details. email@example.com.
Duane Graveline MD MPH
Former USAF Flight Surgeon
Former NASA Astronaut
Retired Family Doctor