Our nervous system is astoundingly complex. It coordinates our movements and sensory information by sending signals to and from the brain to different parts of the body in less than a second. It is made up of the brain, spinal cord, and numerous neural networks throughout the body, providing bi-directional communication to allow us to move, talk, breathe and even understand the world around us. We require both the autonomic branch to control our involuntary responses such as digestion, respiration, and heart rate, as well as the somatic branch to control the voluntary responses such as muscle movements. Due to its complexities, many people suffer from different diseases or syndromes that affect the inner workings of their nervous system.
Postural Orthostatic Tachycardia Syndrome, otherwise known as POTS, is an autonomic disturbance of the nervous system. It is associated with an abnormal increase in heart rate after standing up from a seated or horizontal position (1). Although seemingly straightforward, the syndrome itself is quite complex and not fully understood today by researchers. There is a spectrum of symptoms and severity such that the syndrome affects individuals differently. Some people lose their ability to accomplish their daily chores, go to the gym, and even spend quality time with their friends and family while others can’t even get out of bed in the morning. In order to better untangle the ins and outs of POTS, let’s take a look at the 3 W’s.
What Is It?
As the name describes, postural (relating to the body’s position) orthostatic (relating to the standing position) tachycardia (meaning increased heart rate) syndrome (a collective group of symptoms) is a condition that’s intimately related to a person’s reaction to a relatively significant change in bodily posture. It can be characterized by 2 main parameters (2):
1. A specific group of symptoms experienced frequently upon standing up
2. A heart rate increase of ≥ 30 beats per minute (bpm) when standing up from a horizontal/supine position for 5-30 minutes in adults and > 40 bpm in adolescents (12-19 years). Symptoms should last for ≥ 6 months
Due to the nature of a syndrome, 2 or more symptoms are frequently involved. The most common symptoms associated with POTS include:
– The abnormal increase in heart rate
– Flushing episodes, light-headedness, dizziness
– Nausea and abdominal pain
– Sleeping problems
– Brain fog
– Shaking and abnormal sweating
– Dark blue legs
What’s with the rapid heart rate?
Generally speaking, the hallmark of POTS is an almost immediate increase in heart rate after standing up from a seated or horizontal position. The science behind this phenomenon is due to the shift in blood distribution from our upper body to our lower body upon standing up. Many of the symptoms listed above arise when the heart doesn’t receive an adequate blood supply; for instance, light-headedness, dizziness, fainting, and dark blue legs.
In healthy individuals, the normal response to this orthostatic change is the automatic action of blood vessel vasoconstriction/tightening in order to direct the blood back to the heart. In contrast, people who suffer from POTS have dysfunctional blood vessel activity, causing an abnormal pooling of blood in their lower limbs. In order to compensate for this, heart rate increases rapidly, in the efforts of circulating the blood (3).
Who Does it Affect?
POTS is a common condition affecting millions of people worldwide. Although less common in young children, it’s known to affect adolescents as symptoms begin to develop during and after the onset of puberty. In the more common causes of POTS, it’s seen to affect those between the ages of 12-50 years old. In terms of gender differences, it’s shown to affect women more than men with a female to male ratio of 5:1 (4).
Based on current research, POTS has been shown to run in families; however, no single gene is associated with the majority of cases. There is some evidence in having an association with those with joint hypermobility and mast cell disorders, some of which have a genetic origin (5).
Why Does It Occur?
Unfortunately, there is no clear cause of POTS. Current research has provided plausible causes for some of the more common symptoms that arise from this condition. The primary causes of POTS include mast cell disorders, neuropathy, norepinephrine, nitric oxide, physical deconditioning, and viruses (6).
Mast cell disorders
Mast cells are a group of cells belonging to the immune system. During an allergic reaction, they respond to the local allergen by releasing tiny chemicals that create the redness and itchy sensation. Some of the primary symptoms of POTS tend to exasperate the mast cell response, such as flushing episodes, nausea, and even stomach cramps.
One of the more critical symptoms of POTS is presenting dark blue legs which are associated with the pooling of blood in your lower limbs upon standing up. Feelings of dizziness immediately follow as the blood takes more time to circulate back to the heart and brain. In order to combat this, the heart rate must increase to quickly move the blood back up. In healthy people, this phenomenon doesn’t occur due to the tightening of blood vessels upon standing up to prevent the pooling of blood in the legs. Instead, people dealing with POTS may have lost nerve supply to their blood vessels preventing them to function normally.
Norepinephrine is an excitatory chemical produced during a stress response. Stressors to the body can be as extreme as running away from a bear and as minor as standing up from a seated position. People with POTS tend to have abnormally high levels of norepinephrine, causing these stressors to become less tolerable. Treatment for this is targeted towards the prevention of norepinephrine release.
Nitric oxide (NO) is a chemical produced naturally in our bodies to help regulate our cardiovascular functioning. In healthy humans, NO helps to stabilize blood pressure by causing vasodilation or relaxation of our blood vessels. Research has suggested that during POTS, the interactions between NO and the autonomic nervous system is dysfunctional, elevating some of its symptoms.
Over longer periods of time, physical deconditioning can lead to a smaller heart size which limits your ability to pump blood throughout your body, otherwise known as cardiac output. Remember, your heart is a muscle just like your biceps and triceps – if you don’t use it you lose it (in terms of mass, that is). However, it’s difficult to truly determine if physical deconditioning leads to POTS or the other way around.
As a stressful trigger, viruses and other kinds of infections can contribute to the onset of POTS symptoms. Research has not yet determined the exact mechanisms for this. It is hypothesized that viruses may be damaging the nervous system or triggering antibodies that affect the nervous system. Roughly ⅓ of POTS patients associate the onset of their POTS symptoms with a viral illness.
For the majority of cases, POTS is predominantly seen in people who have experienced high stress in their life – such as following pregnancy, sepsis, fever/illness, surgery, or other physical trauma (7). Secondary causes of POTS include, but are not limited to, adrenal disorders, anemia, autoimmune disorders, gastric bypass surgery, gastric disease, spinal disorder, tumours and even vitamin deficiency.
Assessment and Diagnosis
Due to the wide range of non-specific symptoms that can be experienced by patients with POTS, certain approaches can vary in their rate of success when comparing person to person. This is why a direct and accurate diagnosis is integral before approaching the right therapy. To make this definitive decision, a careful history taking and clinical evaluation is not only important but is essential to your care.
A well-rounded history taking is an initial step towards gaining more insight on a person’s condition if that is in fact what they’re dealing with. Much of this can be done using medical questionnaires. These questionnaires are useful in identifying the relevant symptoms while also discounting other conditions with overlapping symptoms (i.e. chronic fatigue syndrome and fibromyalgia). They help to rule out any other causes for the symptoms you may be experiencing; for instance, tachycardia may be the result of other heart-related conditions such as hypertension (high blood pressure), coronary artery disease (atherosclerosis), heart valve disease, heart failure, heart muscle disease (cardiomyopathy), tumours, or infections (8).
Other useful information includes:
Medications: past or present use of medication, including supplements, can all inform clinicians about symptom onset and even worsening of symptoms.
External Factors: several external factors that come into play that contribute to symptom severity include your daily salt and water intake (causing changes to your blood volume and ultimately cardiac output), sleep quality/circadian rhythms, level of exercise, stress, anxiety, etc.
Genetic Factors: in the majority of cases, POTS does not appear to be directly linked to genetic inheritance. On some occasions, however, people do report a family history of orthostatic intolerance suggesting some inherited factors (9).
Another key variable towards making a POTS diagnosis is the symptom onset. Some people develop symptoms following a period of rapid growth while others have a physical trauma or immunologic trigger (i.e vaccination or virus). Commonly, POTS patients tend to present with a history of prolonged illness.
Two standardized methods of diagnosing POTS are the Head-Up Tilt Table Test (HUT) as well as the standing test (10).
1. The HUT Test
The HUT test is used to assess a patient’s reaction to any postural changes. This test is done by placing a patient on a tilt table and measuring their baseline blood pressure and heart rate. Next, the table is tilted to a 60-80 degree vertical angle for 45 minutes where blood pressure and heart rate are measured a second time. This second measurement is done either continuously or every 2-3 minutes.
2. The Standing Test:
The standing test is a 10-minute test used to mimic real-life circumstances in the efforts of diagnosing POTS patients. During this test, the patient is told to stand upright without any assistance and to support their own weight while maintaining balance.
Keep Moving Forward
POTS can be a debilitating condition that leaves millions of people confused, frustrated, and limited in their ability to live their lives. Understanding your symptoms and taking control early is an essential step towards treating your POTS. The right approach to therapy in complex conditions can be life-changing, to say the least.
COMING SOON: Part 2 – Therapy Options for POTS
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