Understanding Orthostatic Hypotension

Understanding Orthostatic Hypotension
by: Gwendolyn W.
5/22/2008



Orthostatic Intolerance is an umbrella term for several conditions when symptoms worsen in an upright position. The following information explains Neurally Mediated Hypotension (NMH) and Postural Orthostatic Tachycardia Syndrome (POTS) which are two common forms of Orthostatic Hypotension. The medical term for low blood pressure is hypotension and the medical term for an increase in heart rate (HR) is tachycardia.


Understanding POTS:

Postural Orthostatic Tachycardia Syndrome simply means an increased heart rate upon standing. A “healthy” individual has a slight increase in heart rate upon standing by 10-15 beats per minute within 10 minutes. A POTS patient has an increase of heart rate by 30 beats per minute or higher over the first 10 minutes upon standing. POTS is an abnormality in the regulation of heart rate; the heart itself is usually normal. Some POTS patients go onto develop NMH upon standing.


Understanding NMH:

Neurally Mediated Hypotension literally means a drop of blood pressure (BP) in an upright position. It is defined as an drop of systolic (the top number) BP of 25mm HG and is compared the BP of when the patient is laying down. It occurs because too little blood circulates back to the heart and brain.

NMH is also known for these names: the fainting reflex, delayed orthostatic hypotension, neurocardiogenic syncope, vasodepressor syncope, vaso-vagal syncope. The medical term for fainting or passing out is syncope.


Why do upright positions cause problems for these patients?

When a healthy individual stands up, gravity produces approximately 10-15% of his or her blood to settle in the stomach and limbs. This blood pooling means that less blood reaches the brain resulting in lightheadedness, seeing stars, vision tunneling/darkening, and sometimes fainting. For healthy individuals the above symptoms are un-common when standing up because the leg muscles pump blood back up to the heart. Another reason is because one’s body turns on a series of rapid quick reflex motions to make up for the lower amount of blood returning back to the heart upon standing. One’s body releases norepinephrine and epinephrine which is also known as adrenaline. The norepinephrine and epinephrine cause the heart to beat a little quicker and with more force- a feeling which is familiar after exercising or being frightened. This causes blood vessels to constrict (tighten). The end result is more blood returning to the brain and heart. Usually healthy individuals are unaware of the changing reflexes when they stand up.

When someone with NMH or POTS stands up, they tend to pool a larger amount of blood in vessels beneath the heart. Compared to healthy individuals, those with NMH and POTS, more blood tends to settle in the stomach and limbs the longer they are in an upright position. Like we learned earlier the body responds by releasing norepinephrine and epinephrine in an attempt to cause more constriction of the blood vessels. For many reason which all are not very well understood yet, the blood vessels do not respond correctly to the release of norepinephrine and epinephrine. In NMH and POTS patients the blood vessels tend to either constrict or not constrict and sometimes they dilate instead.

In patients with POTS, the result of excessive blood pooling when in an upright position means an increase of their heart rate. With NMH, the result is in the lowering of blood pressure. This is all caused because of a “miscommunication” between the heart and brain-both are usually normal in structure. The heart needs to beat faster to pump blood to the brain to prevent fainting. The brain sends out a message that the heart rate should be slowed down and that the blood vessels should dilate even more. This takes even more blood away from the central part of circulation where it is needed most. It is not clear why people develop NMH and POTS but it may all be from the relationship of the norepinephrine and epinephrine release in the body.

Symptoms of NMH and POTS:

• lightheadedness or a spacey feeling
• dizziness
• fainting/near fainting
• dimming of vision
• nausea or vomiting
• fatigue that can last for days
• exercise intolerance
• muscle aches
• headaches/migraines
• tachycardia
• palpitations
• bradycardia
• weakness
• shakiness
• clamminess
• anxiety
• shortness of breath
• mental confusion such as: brain fog, trouble staying on task, remembering, and finding the right words to say, difficulty concentrating
• chest pain or chest tightness
• Gastrointestinal problems
• sleeping disorders
• lower back pain
• excessive fatigue
• intolerance to heat
• light and noise sensitivity


It has been discovered that there is a large overlap between syndromes of Orthostatic Hypotension and Chronic Fatigue Syndrome (CFS) and Fibromyalgia (FM). Not all patients with NMH or POTS have CFS or FM and not all with CFS or FM have NMH or POTS.

NMH and POTS symptoms that can be triggered by the following:

• standing in long lines
• taking a hot shower
• hot tubs, saunas etc.
• sitting too long
• being in an warm or hot environment
• stressful events
• lack of fluid and salt intake
• eating large meals
• bending down
• blowing up balloons
• vasodilating medications
• drinking alcohol
• caffeine makes some patients feel worse
• bending up and down
• climbing stairs
• giving blood
• singing



How are NMH and POTS diagnosed?

NMH and POTS cannot be detected without a prolonged standing test or tilt table test (ttt). To diagnose POTS a 10 minute test is usually all that is needed. However, to diagnose NMH a longer period of time will be needed.

A tilt table test is not much fun but it is the way to diagnose NMH and POTS. The ttt includes laying down on a table then being strapped down because the table is then raised 70˚so you are basically standing upright. It is best if you are strapped down because the goal of the test is to pass out. Durring the test you are required to stay as still as possible. The tilt table technicians may ask you how you are feeling every once in a while but other then that, you are expected to remain silent. While you are on the tt, they monitor your BP and HR very closely.


What causes NMH and POTS?

At present this answer isn’t very well understood. It is suspected that NMH and POTS are genetic in many patients but that isn’t always the case. There has been no gene yet to be found for patients with NMH but there is a link in patients with POTS who have joint mobility or Ehlers- Danlos Syndrome (EDS). Some patients reported that after being sick with the flu, mononucleosis, or being in a car accident or having surgery that this bring on symptoms. Another suspicion is that

Some researches have noted an overlap in spinal stenosis and Chiari Malformation. We do not know why these conditions cause NMH and POTS but it is being researched.

Most importantly talk to a health care provider who understands NMH and POTS. Sometimes medications are not needed; increasing fluid intake such as drinking Gatorade, Pedialyte, and water and also increasing your salt intake are enough. Others may need to take medications to help control their symptoms.