Orthostatic Intolerance (OI) is a condition in which an upright position causes hypotension. Orthostatic intolerance is an umbrella term which pertains to both Neurally Mediated Hypotension (NMH) and Postural Orthostatic Tachycardia Syndrome (POTS). In this article we will be discussing NMH and POTS in a synopsis of the article, “General Information Brochure on Orthostatic Intolerance and Its Treatment” written by Peter C. Rowe from John Hopkins Children's Center.
(Disclaimer: I am not a medical professional and all the information in this post comes from the referenced article. The link to the full article can be found in the “references” section of this post.)
Neurally Mediated Hypotension
NMH pertains to a drop in blood pressure after a period of being in an upright position. NMH is defined by a drop in systolic blood pressure of 25mm Hg during a tilt table test or standing. Most people who develop NMH have a normal resting blood pressure, although the condition may be slightly more common in individuals with low blood pressure. NMH is caused by a miscommunication between the brain and the heart that results in an improper regulation of blood pressure while being in an upright position.
Postural Orthostatic Tachycardia Syndrome
POTS pertains to an excessive increase in heart rate upon standing. POTS is defined by an increase of 40bmp in adolescents, 30bpm in adults, or a heart rate of over 120bpm within the first 10 minutes of standing, along with orthostatic symptoms. The heart of POTS patients is typically normal, with the problem lying in the regulation of heart rate. During an upright standing or tilt table test, some POTS patients will develop NMH if the test is continued after the first 10 minutes. These two conditions are not mutually exclusive and often present together.
How Do Postural Changes Cause These Problems?
It is normal for 10-15% of blood to pool in the abdomen, arms, and legs upon standing in healthy individuals. The body responds to this blood pooling by releasing a surge of adrenaline hormones which cause an increase in heart rate along with constriction of the blood vessels. These rapid reflex responses quickly send blood back to the heart and brain to maintain optimal functioning.
However, in POTS or NMH patients, there appears to be a larger than normal quantity of blood that settles below the heart upon standing. Typically, the longer the patient is upright, the more blood pools beneath the heart. In response to these changes, the body releases more adrenaline in an attempt to constrict blood vessels and send blood back to the heart. When this surge of adrenaline is produced, the blood vessels either constrict inefficiently or dilate. Because the blood vessels respond inefficiently, the heart rate will often increase in an attempt to compensate and restore proper blood flow.
In POTS patients, the typical response to blood pooling is a drastic increase in heart rate, whereas in NMH this results in a reflex that lowers blood pressure. These responses are the result of a miscommunication in between the heart and brain that cause improper responses to the stressor. It is not clear why some people develop POTS versus NMH, but it is hypothesized to be because of the balance of adrenaline hormones within the body.
Symptoms of POTS and NMH
There is a large degree of overlap between the symptoms of POTS and NMH such as fatigue, lightheadedness, mental fog, fainting, and headaches. In POTS, the trademark symptoms are tachycardia and/or heart palpitations which can also present with symptoms such as weakness, balance issues, exercise intolerance, shakiness, anxiety, shortness of breath, clamminess, and blurred vision. With NMH you may see chronic fatigue, muscle aches, and nausea.
There also seems to be significant overlap between Orthostatic Intolerance and the presence of Chronic Fatigue Syndrome or Fibromyalgia. However, while it is common for these conditions to present together, that is not always the case.
Patients may see symptoms become worse after activities such as:
Maintaining a stagnant upright posture (e.g. standing in line)
After exercise
Being in a hot environment
After eating
After a stressful event
How Are POTS and NMH diagnosed?
POTS and NMH are both diagnosed with a prolonged standing or tilt table test. NMH usually requires at least 45 minutes of upright posture, whereas POTS typically only requires 10 minutes for symptoms to present.
What Causes POTS and NMH?
There is no clear understanding of why these conditions develop currently, but it is possible that it is genetic. Joint hypermobility syndrome is commonly seen in patients with Chronic Fatigue Syndrome and/or Orthostatic Intolerance. The presence of joint hypermobility provides further evidence of there being a genetic component to these illnesses.
How Are POTS and NMH Treated?
Because of the complexity of these illnesses, the treatment approach must be tailored to each patient, but in general treatment follows a three step approach. Step 1 focuses on non-pharmaceutical treatments and is mainly focused on lifestyle changes. Steps 2 and 3 are used on patients who do not respond well enough with just lifestyle changes and are focused around finding a medication combination that relieves symptoms. The treatment of other underlying conditions such as infections, asthma, and allergies is also fundamental in managing the Orthostatic Intolerance.
References
General Information Brochure on Orthostatic Intolerance and Its Treatment. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf.
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