POTS
Postural Orthostatic Tachycardia Syndrome (POTS) Part I
Many people suffer from what is termed dysautonomia. This is an umbrella term used to describe any disease or malfunctioning of the autonomic nervous system. Our nervous systems are comprised of different parts:
The autonomic nervous system is the part of the system that’s responsible for master regulation of organ function and thus the control of the bodily functions that aren’t consciously directed, such as breathing, the heartbeat, temperature regulation, and the digestive processes.
Dysautonomia is a full body condition, affecting the malfunctioning of many or all of the organs under the body’s control. Due to multiorgan system involvement, patients often present with numerous, seemingly unrelated, maladies. Dysautonomia has this feature in common with MCAS. Patients are often consulting a variety of doctors, each specializing in a different organ system, none of whom view the symptom presentation as a whole-body system involvement.
Dysautonomia is quite common and can include conditions such as vasovagal syncope, sinus tachycardia, orthostatic hypotension, diabetic autonomic neuropathy, neurocardiogenic syncope (NCS), mitral valve prolapse dysautonomia, and postural orthostatic tachycardia syndrome (POTS), the subject of today’s essay.
Simply put, POTS is the body’s inability to make the necessary adjustments to counteract gravity when standing up.
Dysautonomia is often associated with other disease processes such as Lyme disease, primary biliary cirrhosis, multiple system atrophy (Shy-Drager syndrome), Ehlers-Danlos syndrome, and Marfan syndrome.
POTS isn’t a rare condition but often isn’t considered, understood, or accurately diagnosed by primary healthcare providers. Most doctors don’t routinely think about it or test for the condition in their offices. A missed diagnosis of POTS (as well as that of orthostatic hypotension) can have devastating consequences for an individual’s health issues and prospects of recovery. In fact, my experience is that without recognition and adequate treatment of this condition, very little can be achieved regarding recovery for those suffering from complex, chronic health issues, where POTS is frequently a dominant co-morbid condition that’s notoriously underdiagnosed. This condition is often accompanied by a high degree of functional disability, appearing under the radar and masquerading as many other health conditions, most commonly referred to as psychosomatic, a cruel diagnosis to assign to a person that has very real biological and physiological imbalances.
POTS was first described in the 1860s and initially named Civil War Syndrome and Effort Syndrome, among other names.[i] It was also often called neurasthenia. Prevalence is estimated to be at around 0.3 percent of the U.S. population, affecting around three million people. However, within the population with chronic, complex illness that present themselves at my clinic, the prevalence is much higher, approaching ten to twenty percent. The condition is most often diagnosed in younger females, with onset occurring between fifteen and forty-five years of age.[ii]
POTS is a complex condition that can drastically affect the day-to-day lives of those that suffer from it. POTS is a type of orthostatic intolerance, which means that it gets worse when people who have the condition are standing, or when they move from a lying or sitting position to a standing position.
The two broad classifications for POTS are for those individuals who have the condition all the time (non-positional), and those who have it only with positional changes.[iii]
One of the main characteristics of the condition is that the main focus is on the sympathetic nervous system activation, which characterizes the disorder.[iv] In emergency rooms and primary care clinics, it’s one of the most common presentations of syncope and pre-syncope. This refers to the patient feeling faint, but not quite passing out.
POTS is often described as a clinical syndrome consisting of multiple heterogeneous disorders. In addition, there are several possible underlying pathophysiological processes underlying the condition, including partial sympathetic neuropathy, hyperadrenergic state, hypovolemia, mast cell activation, deconditioning, and immune-mediated.[v] Many clinical features may overlap, making it difficult to categorize exactly what aspects are activated at any particular time. The good news is that although POTS may be extremely unpleasant to live with, limiting many activities associated with daily living, POTS isn’t associated with mortality. Patients can make significant symptomatic improvements over time, once the condition has been diagnosed and treated appropriately.
In addition to POTS, there are other conditions of orthostatic intolerance, like orthostatic hypotension. These conditions are also frequently seen with other ‘invisible’ conditions, such as Ehlers-Danlos syndrome, chronic fatigue syndrome, migraine, fibromyalgia, autoimmune disorders, irritable bowel syndrome (IBS), food allergies, and mast cell activation syndrome (MCAS). Please see my other articles related to MCAS.
In this two-part series, I’ll be discussing the etiology of POTS, how it manifests in most people, the common comorbid conditions it’s often seen with, and how to diagnose and treat the condition.
In this first part you’ll learn:
As I already mentioned, POTS is a type of orthostatic intolerance. This means that it gets worse when people with the condition are in a standing position or when they get up from a lying or seated position.
With POTS, the heart rate increases rapidly when standing, by at least an additional thirty beats per minute compared to sitting, or up to 120 beats per minute within ten minutes. Tachycardia is the medical term for an increased heart rate.[vi]
The strict criteria for making the diagnosis are as follows:
The pathophysiology pf POTS is complex but it appears to revolve around three central mechanisms:
For a diagnosis of POTS to be made, the increased pulse rate must be sustained for longer than ten minutes, sometimes noted to be increased for up to thirty minutes. Many people will have a transient increase in pulse rate within forty-five seconds of standing, but it isn’t sustained and is often associated with a transient drop of blood pressure, which indicates a variant of orthostatic hypotension. Many patients with POTS will also have orthostatic hypotension, especially if associated with hypovolemia. However, if the increased pulse rate is less than thirty beats from baseline and is only associated with a drop in blood pressure, then this isn’t considered to constitute a diagnosis of POTS. Furthermore, in order to consider a diagnosis of POTS, the symptoms must be chronic in nature. Many people will experience transient POTS-like symptoms such as with a viral infection, which often resolve in a few days. Sometimes POTS may even be accompanied by a small rise in systolic blood pressure.
Tachycardia is thought to occur because of the pooling of blood below the heart. In response to this pooling, the body releases norepinephrine and epinephrine in order to constrict the peripheral blood vessels and send blood pumping throughout the body again. However, in POTS and other orthostatic conditions, the vessels don’t respond properly to this increase of epinephrine and norepinephrine, so the blood vessels don’t constrict and blood remains pooled below the heart.
However, in POTS specifically, the heart still has a normal reaction to the norepinephrine and epinephrine, although the peripheral vessels don’t constrict appropriately and so the heartbeat quickens.[viii] Patients with POTS will often have high upright levels of plasma norepinephrine, reflecting sympathetic nervous system activation. In addition, some patients may have a dramatic response to eating food, whereby they can experience debilitating fatigue postprandial. This occurs because in the process of digesting a meal, a large amount of blood is diverted away from other areas of the body to the gastrointestinal tract, depriving the brain and the peripheral mitochondria of blood flow and hence energy, in order to run the rest of the individual’s physiology.
There are four types of POTS:[ix]
This type of POTS may be caused by nerve damage that interferes with the blood vessels’ ability to constrict, as well as resulting from poor parasympathetic vagal tone and low levels of the neurotransmitter acetylcholine.
This is POTS that’s associated with high levels of sympathetic nervous system overdrive and the production of adrenaline and norepinephrine.
This type of POTS occurs as a result of low blood volume. This has often been found to be associated with physical deconditioning.[x] It can also be associated with significant upright GI symptoms.
This type of POTS is caused by another disease, like diabetes or Lyme disease.
It’s also important to note that POTS doesn’t usually occur as a result of any physical malformations of the blood vessels or heart, but rather as a result of functional abnormalities.
POTS is most commonly seen in women between the ages of fifteen and forty-five years old, mostly during child bearing years, and is thought to be widely prevalent. However, the exact statistics regarding the prevalence of the condition in the United States and Canada aren’t known because it’s likely that many people with POTS are misdiagnosed or undiagnosed.[xi] A family history is reported in thirteen percent of patients.[xii]
Some of the signs and symptoms of POTS include:[xiii]
These symptoms don’t typically occur when a person is sitting or lying down, but they can be triggered by standing, exercise, stressful events, or warm environments. Approximately a quarter of blood volume resides in the chest when in the supine position. Upon standing and due to the effects of gravity, there’s an immediate shift of 500 to 1000 ml of blood from the chest cavity to the vessels in the lower extremities, buttocks, and lower abdomen. This leads to impaired venous blood return to the heart, with a resultant drop in blood pressure. There’s also a ten to twenty-five percent shift of plasma volume out of the vasculature and into the interstitial tissue.
When you stand up, gravity causes blood flow to be pulled downwards. For someone with poor parasympathetic vagus nerve injury with low acetylcholine production, this shift decreases venous return to the heart. This in turn results in a transient decrease in both arterial pressure and cardiac filling, reduced blood flow to the head, and an increased pooling of blood in the lower part of the body.
One of the consequences of blood pooling in the venous system is that it struggles to fill the heart. If the system fails to do this, the heart tries to compensate by increasing its heart rate to keep up the cardiac output. However, it usually still fails because if the blood isn’t there to fill the heart, the cardiac output is still going to drop, no matter how fast the heart goes.
In a healthy person, the autonomic nervous system compensates for these hemodynamic changes by stimulating the sympathetic (fight/flight) nervous system to release adrenaline to vasoconstrict the peripheral blood vessels, speed up the heart rate, and suppress the parasympathetic (rest/digest) nervous system. This facilitates an increased return of blood flow to the heart to counteract the initial decline in blood pressure. If the dynamics are working properly, these compensatory changes result in negligible changes in systolic and diastolic blood pressures with a normal ten to twenty beats per minute increase in the pulse rate when standing and a 5 mm Hg increase in diastolic blood pressure.
However, as with POTS, if there are any abnormalities of the autonomic nervous system’s regulation of these hemodynamics, a resultant fall in blood pressure can occur, as well as the increased pulse rate as seen in POTS.
The body then tries to compensate for that as best it can by revving up the sympathetic nervous system, secreting a significant amount of adrenaline and noradrenaline. The consequence of these adrenaline surges is a lot of anxiety, a racing heart, heart palpitations, and insomnia. These are the consequences of compensatory sympathetic overdrive.
As already mentioned, POTS symptoms may also be triggered after eating. This is because blood flow is redirected to the digestive tract, or if a person with POTS isn’t drinking enough fluid or getting enough salt in their diet.[xvii]
GI motility abnormalities appear to be a significant driver of POTS symptoms in both the orthostatic and the non-positional types of the condition. Many studies using combined 24-hour antroduodenal manometry (ADM), the study of stomach and small bowel motility, and TILT (TTT) table testing, have proven this association.[xviii] Even among patients whose gastric motility studies were normal at baseline, sixty-eight percent became abnormal during the TTT. Gastrointestinal symptoms of nausea/vomiting and abdominal pain were reproduced in eighty-nine percent of subjects during TTT. Vomiting was significantly more frequent in those with delayed gastric emptying, which is defined as greater than or equal to a ten percent retention of food in the stomach at four hours post ingestion.
Interestingly, women with POTS often report that they feel better than ever when they’re pregnant. This is because there’s a natural increase in blood volume during pregnancy, which helps to ease their symptoms. However, women who aren’t pregnant may experience a worsening of their POTS symptoms when their menstrual cycle begins.[xix]
Symptoms may also be worsened by dehydration, exercise, alcohol intake, heat exposure, asthma, allergies, endometriosis and pelvic congestion syndrome in women, migraines, depression, anxiety, concussions, and sinusitis. However, there are many other conditions that aren’t listed here that may make the symptoms of POTS worse.[xx]
POTS may seem like a minor issue if you’ve never dealt with it before, but that’s actually far from the reality faced by those suffering from POTS. The condition can be profoundly impactful, severely interrupting the lives of people with POTS. Consider how your life would change if you couldn’t stand for more than ten minutes or spend any amount of time in hot weather. There would be no waiting in line, no walking your dog or walking around the block, no shopping, and no sports. Even attempting to take a vacation would be a significant challenge. Or what if merely eating a meal was enough to leave you fatigued for the rest of the day?[xxi]
For people with severe POTS, their quality of life can be seriously affected. In fact, some physicians have compared the level of disability accompanying POTS to that of chronic obstructive pulmonary disease (COPD), an obstructive airway disease that limits breathing and can deprive the body of oxygen. Additionally, some researchers have surmised that the quality of life of people with severe POTS is approximately the same as the quality of life of people with kidney failure who are on dialysis.[xxii]
POTS and other conditions are often seen together in patients. Because POTS isn’t a disease itself, it doesn’t typically develop in the absence of any other diseases, conditions, or health factors. There’s always a causal factor, be it genetics, another condition or disease, or an illness or injury trigger.
POTS isn’t the only orthostatic intolerance condition. Orthostatic hypotension and sinus tachycardia syndrome, while similar to POTS, are different conditions. Although these conditions are similar to POTS, with similar signs and symptoms, they’re not identical.
Orthostatic hypotension is characterized by a decline in blood pressure of more than 20 m (systolic) /10 (diastolic) mmHg while standing rather than an increase in heart rate.[xxiii] This condition usually results from autonomic failure and the changes are often far greater than those mentioned above, resulting in a temporarily loss of consciousness soon after standing.
Sinus tachycardia syndrome is when your body sends out electrical impulses that cause your heart to beat faster, typically at rest, but without cause. It’s normal for your body to send out these impulses in response to exercise, stress, or fever, but abnormal for these electrical signals to occur in the absence of these external triggers.[xxiv]
In some people, POTS and mast cell activation syndrome are seen together. This is fairly common for people with hyperadrenergic POTS. These patients often exhibit severe flushing or redness during standing, along with an increased heart rate, diarrhea, abdominal cramping, and nausea.
Mast cells are a type of white cell representing one percent of the total white cell count. They’re found in all vascularized tissue throughout the body at the junction point of the host and the external environment at points of entry of a toxin or antigen. They’re particularly represented in the mucosal and the epithelial cells, such as those in the respiratory tract, the skin, and in the GI tract, particularly in the duodenum. These cells are involved in defending the host from incoming toxins of any kind.
MCAS is an abnormal activation of the mast cells, which when activated on mast cell receptors by triggers, of which there are many, degranulate and release into the extracellular matrix potent mediators of inflammation, anticoagulation, and vasodilatation such as histamine and tryptase, heparin, proteases, enzymes, prostaglandins, eicosanoids, cytokines, growth factors, and reactive oxygen species, otherwise known as ‘free radicals’. In many cases where histamine is involved, it can cause a response similar to an allergic reaction. In severe cases, people with MCAS are considered to be ‘allergic to everything’. Mast cells seem to degranulate more severely when a patient is upright with hypotension and tachycardia.[xxv]
In addition to all the standard POTS symptoms, those with MCAS may also have gastrointestinal symptoms. The following paragraph explains how MCAS can result in GI symptoms, skin reactions, hives, and angioedema, often seen as accompanying conditions with those suffering from POTS.
When the gastrointestinal tract is exposed to an antigen, its response is to increase fluid secretion, increase smooth muscle contraction, and increase peristalsis. Proteins derived from different plants and animals can act as antigens and activate the immune system in vulnerable subjects. The antigen (peptide) permeates through the epithelial layer of the mucosa of the gut and binds to IgE on mucosal mast cells. These peptides are presented to Th2 cells, and if there is an IgE antibody against the peptide present, it will cause activation of the mast cell resulting in an immune response. This causes mast cells to degranulate and release a variety of inflammatory mediators. These mediators increase vascular permeability, causing edema in the gut epithelium and smooth muscle contraction, which lead to vomiting and diarrhea. This type of reaction can occur in response to peptides found in certain medications. Food allergens can also cause skin reactions. Uptake from the gastrointestinal tract can introduce antigens into the blood, which are transported throughout the body where they bind to IgE on mast cells in the connective tissue in the deep layers of the skin. This results in urticarial reaction and angioedema. [xxvi]
Researchers are still studying how exactly POTS and MCAS interact with one another, along with whether one causes the other or if they might occur side-by-side in response to some other type of trigger, such as mitochondrial dysfunction. It’s been speculated that chronic exposure to prostaglandins and histamines affect the connective tissue and vasculature in the GI tract, resulting in conditions such as chronic constipation. Whenever a patient is seen with chronic GI symptoms, POTS, and MCAS, it’s imperative that the pathologist restain the GI tract biopsy specimens for CD 117 cells, which is a sure way to quantify the number of mast cells seen per high-power field in the biopsy specimen. If more than twenty mast cells are seen in a specimen stained in this way, it’s a clear indication that the person is suffering from MCAS. My blogs on MCAS provide a more detailed explanation regarding this. It has been referenced that an estimated nine percent of POTS patients have MCAS,[xxvii] although in my clinical experience it’s more like fifty percent. Avoiding certain food and gut bacterial antigen triggers can have a dramatic effect on reducing these symptoms. Please see the recent paper published by Dr. Afrin, with myself and others as co-authors, on the Consensus-2 criteria for the diagnosis of MCAS, entitled Diagnosis of mast cell activation syndrome: a global “consensus-2”[xxviii]
Formal diagnosis of MCAS requires fulfilling the major criteria, which is having characteristics of mast cell activation symptoms in two or more systems, along with one minor criteria.[xxix] Minor criteria include have more than twenty mast cells per high-powered field using the CD 117 immunohistochemical staining from a specimen collected from the second part of the duodenum, having an elevated number of mast cells mediators in the blood or urine, or document of improvement of symptoms with mast cell stabilizers.[xxx]
In addition to MCAS, several other conditions may be present with POTS.
POTS can lead to extreme fatigue, and people with POTS report poorer quality of sleep. CFS is commonly noted alongside POTS for these reasons. In fact, people who have been diagnosed with CFS and people who have been diagnosed with POTS tend to have similar symptoms when standing, leading some researchers to conclude that CFS may be part of the clinical presentation of POTS.[xxxi]
Ehlers-Danlos syndromes are a group of inheritable connective tissue disorders characterized by joint hypermobility, skin hyperextensibility and tissue fragility with an incidence of 1 in 500. [xxxii] Joint Hypermobility Syndrome (JHS), synonymous with Ehlers-Danlos Hypermobile Type, formerly Type III (hEDS III), is the most commonly seen subset involving hypermobility of the musculoskeletal system and is associated with abnormal collagen formation and autonomic nervous systems abnormalities. Please see the paper entitled Neurovisceral phenotypes in the expression of psychiatric symptoms[xxxiii]for a table outlining the criteria for making diagnosis of JHS/EDSIII.
People with EDS often have symptoms of orthostatic intolerance, including POTS. Their symptoms can also be exacerbated by physical activity, eating, standing, and warm environments. According to one study, eighteen to twenty-five percent of POTS patients also meet the criteria for an EDS diagnosis, EDS-type III, characterized by hypermobility, is the most common condition that’s associated with POTS. The vast majority of hEDS patients also have gastrointestinal symptoms and if seen together with POTS, these symptoms are amplified. GI conditions such as irritable bowel syndrome (IBS), functional constipation, and GERD are prevalent in forty-eight, thirty-six, and seventy-eight percent respectively.[xxxiv]
There are various theories regarding why hEDS and the manifestation of GI symptoms, ranging from connective tissue abnormalities, lead to laxity increase in the GI tract with resultant mechanical dysfunction and altered motility. In addition, it’s known that neuronal development in the enteric nervous system is dependent on normal collagen formation.
Patients with concomitant POTS and hEDS were younger in age and had a higher prevalence of chronic fatigue syndrome, fibromyalgia, and depression. Symptoms such as functional dyspepsia, chronic nausea and vomiting syndrome, functional heartburn, dysphagia, fecal incontinence, and levator ani syndrome were all higher in the hEDS-POTS cohort.[xxxv]
Other conditions that have been associated with joint hypermobility include ADHD, anxiety, asthma, carpal tunnel syndrome, chiari malformation type I, chronic fatigue syndrome, chronic regional pain syndromes, Crohns disease, hiatus hernia, mitral valve prolapse, migraine, headaches, pelvic organ prolapse, rectal evacuatory dysfunction, and urinary stress incontinence.[xxxvi]
Median Arcuate Ligament syndrome (MALS). Median arcuate ligament syndrome (MALS) occurs when the arc-shaped band of tissue in the chest area, known as the median arcuate ligament, presses on the artery that sends blood to the upper abdomen. The artery is called the celiac artery. MALS can cause stomach pain in some people.[xxxvii]
Vasovagal syncope is a disorder characterized by sudden, sharp declines in blood pressure that lead to fainting episodes. Although POTS is primarily characterized by heart rate increases, people with POTS may also have vasovagal syncope or orthostatic hypotension, which can also lead to fainting.[xxxviii]
Fibromyalgia is a condition that’s characterized by muscle pain of an unknown cause. Like CFS, it’s commonly seen in people with orthostatic intolerance conditions, like POTS. Researchers theorize that POTS with fibromyalgia may be caused by neuroinflammation, which can occur after a triggering event like a viral infection.[xxxix]
Other conditions include migraine headaches, celiac disease and/or gluten sensitivity, gastroesophageal disease, and peptic ulcer disease. An ever-increasing number of COVID-19 patients are also now seen to have symptoms suggestive of POTS[xl]
Recently, a group of physicians have observed a strong relationship between Hypermobile Ehlers-Danlos Syndrome, Postural Orthostatic Tachycardia, and Mast Cell Activation syndrome, naming this as the triad of conditions. If further autoimmune conditions and gastric motility issues were noted, this has been referred to as a pentad of conditions. Dr Andrew Maxwell has an excellent PowerPoint describing these associated conditions.
POTS isn’t a disease itself, but rather a cluster of symptoms. It can be caused by any manner of other conditions, and may even be caused by genetics or trauma. Here are some of the many potential causes of POTS:[xli]
Some of the known diagnoses that may cause secondary POTS include heavy metal toxicity, amyloidosis, Sjogren syndrome, sarcoidosis, and lupus. Alcohol abuse may also increase a person’s risk of POTS, as well as a history of chemotherapy use.
Unfortunately, there’s still a great deal that we don’t understand about the pathophysiology of POTS and exactly what causes it.
POTS is diagnosed by taking a thorough history, using a POTS questionnaire such as the Self-Report Orthostatic Grading Scale,[xliii] and by performing a physical examination during which orthostatic vital signs are recorded. POTS is often associated with hypermobility syndromes, so an examination using the Beighton Score is essential.
Specific diagnostic tests include a standing test or a tilt-table test with a 12 lead ECG.[xliv]
With a standing test, the patient lies down for a few minutes before their pulse and blood pressure are recorded with an electronic device, such as the Omron blood pressure machine. They then stand up and while not holding onto anything, and without talking or moving too much, their pulse and blood pressure are recorded at one, three, five, and ten minute intervals. Since POTS may be influenced by diurnal variations, with the morning being the most sensitive time of day, it may increase diagnostic accuracy if the readings are taken in the morning.
A tilt-table test is considered to be the gold standard test for confirming the diagnosis. During this test, the patient is strapped standing up to a table and connected to monitoring equipment, which checks their vital signs at regular intervals. The patient rests while standing up for twenty minutes, before the table is then tilted to seventy degrees. Blood pressure and heart rate are monitored continuously and recorded at two, five, and ten minute intervals. The patient is kept in an upright position for forty minutes or until they faint.
The test is considered positive if the diagnostic criteria are met. Keeping the patient still on the table prevents fidgeting or any compensatory movements to which the patient may have grown accustomed to help ease their symptoms. Keeping them still enables the full magnitude of the patient’s symptoms to be assessed. The tilt-table test is most commonly used for people who experience frequent fainting episodes.
Each of these tests are brief when assessing POTS, taking only about ten to fifteen minutes. However, if other orthostatic syndromes are a possibility, these tests may take significantly longer. In the case of orthostatic hypotension, tests may take up to forty-five minutes.
People with POTS may also experience minor increases in blood pressure when standing. In addition, they will often have elevated blood levels of norepinephrine.[xlv]
There’s much more to POTS than meets the eye. It’s a complex condition characterized by an increased heart rate while standing, but it’s also associated with a number of other conditions and disorders. These include mast cell activation syndrome, chronic fatigue syndrome, Ehrler-Danlos syndrome, and fibromyalgia.
In this first part, we reviewed the definition of POTS, along with signs and symptoms, complications, associated conditions, and how to diagnose POTS. In Part Two, we’ll be reviewing how POTS is treated. It’s a multi-faceted treatment that may include diet changes, specialized compression clothing, strict exercise routines, pharmaceuticals, or indeed all of these.
In the meantime, please reach out to my office if you suspect POTS or if you need help managing your POTS. There’s no need to suffer in silence.
Please watch Dr. Andy Maxwell’s presentation.
[i] Fedorowski A. Postural orthostatic tachycardia syndrome: clinical presentation, aetiology and management. J Internal Med.2019: 285(4):352-366
[ii] Fedorowski A. Postural orthostatic tachycardia syndrome: clinical presentation, aetiology and management. J Internal Med.2019: 285(4):352-366
[iii] Tu Y. Abell T, Raj S, Mar P. Mechanisms and management of gastrointestinal symptoms in postural orthostatic tachycardia syndrome Neurogastroenterology & Motility 2020: \00e14031.
[iv] Raj S. The Postural Tachycardia Syndrome (POTS): Pathophysiology, Diagnosis and Management. Indian Pacing Electrophys J 2006 April-Jun; 6 (2): 84-99.
[v] Arnold A, Ng J, Raj S., Postural tachycardia syndrome – Diagnosis, physiology, and prognosis. Autonomic Neuroscience: Basic and Clinical 215 (2018) 3-11
[vi] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[vii] Mar Pl, Raj SR. Postural orthostatic tachycardia syndrome: mechanisms and new therapies. Annu Rec\v Med. 2020; 71: 235-248
[viii] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[ix] Johns Hopkins Medicine. Postural orthostatic tachycardia syndrome (POTS). N.d. Accessed March 2021. https://www.hopkinsmedicine.org/health/conditions-and-diseases/postural-orthostatic-tachycardia-syndrome-pots
[x] Ibid.
[xi] Cedars Sinai. Postural orthostatic tachycardia syndrome (POTS). N.d. Accessed March 2021. https://www.cedars-sinai.org/health-library/diseases-and-conditions/p/postural-orthostatic-tachycardia-syndrome-pots.html
[xii] Ibid pg. 4
[xiii] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[xiv] Ibid pg. 4
[xv] DiBlaise JK, Harris LA, Goodman B. Postural Tachycardia Syndrome (POTS) and the GI Tract: a primer for the gastroenterologist. Am J Gastroenterol. 2028;113(10):1458-1467
[xvi] Tu Y. Abell T, Raj S, Mar P. Mechanisms and management of gastrointestinal symptoms in postural orthostatic tachycardia syndrome Neurogastroenterology & Motility 2020: \00e14031.
[xvii] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[xviii] Moak JP. Fabian RR, Clarke LC et al. Antroduodenal manometry is abnormal in children presenting with orthostatic intolerance and gastrointestinal symptoms. J Pediatric Gastroenterol Nutr. 2016:63 (3):329-335
[xix] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[xx] Cedars Sinai. Postural orthostatic tachycardia syndrome (POTS). N.d. Accessed March 2021. https://www.cedars-sinai.org/health-library/diseases-and-conditions/p/postural-orthostatic-tachycardia-syndrome-pots.html
[xxi] Dysautonomia International. Postural orthostatic tachycardia syndrome. N.d. Accessed March 2021. http://www.dysautonomiainternational.org/page.php?ID=30
[xxii] Dysautonomia International. Postural orthostatic tachycardia syndrome. N.d. Accessed March 2021. http://www.dysautonomiainternational.org/page.php?ID=30
[xxiii] Arnold AC, Raj SR. Orthostatic Hypotension: A Practical Approach to Investigation and Management. Can J Cardiol. 2017;33(12):1725-1728. doi:10.1016/j.cjca.2017.05.007
[xxiv] Garland EM, Celedonio JE, Raj SR. Postural Tachycardia Syndrome: Beyond Orthostatic Intolerance. Curr Neurol Neurosci Rep. 2015;15(9):60. doi:10.1007/s11910-015-0583-8
[xxv] Tu Y. Abell T, Raj S, Mar P. Mechanisms and management of gastrointestinal symptoms in postural orthostatic tachycardia syndrome Neurogastroenterology & Motility 2020: \00e14031
[xxvi] https://www.frontiersin.org/articles/10.3389/fimmu.2015.00620/full
[xxvii] Shaw BH, Stiles LE, Bourne K, et al. The face of postural tachycardia syndrome- insights from a large cross-sectional community-based survey. J Intern Med. 2019; 286 (4): 438-448
[xxviii] https://www.degruyter.com/document/doi/10.1515/dx-2020-0005/html
[xxix] Tu Y. Abell T, Raj S, Mar P. Mechanisms and management of gastrointestinal symptoms in postural orthostatic tachycardia syndrome Neurogastroenterology & Motility 2020: \00e14031
[xxx] Weinstock LB, Pace LA,Rezaie A, Afrin LB, Molderings GJ. Mast cell activation syndrome: a primer for the gastroenterologist. Dig Dis Sci.2020
[xxxi] Garland EM, Celedonio JE, Raj SR. Postural Tachycardia Syndrome: Beyond Orthostatic Intolerance. Curr Neurol Neurosci Rep. 2015;15(9):60. doi:10.1007/s11910-015-0583-8
[xxxii] Tu Y. Abell T, Raj S, Mar P. Mechanisms and management of gastrointestinal symptoms in postural orthostatic tachycardia syndrome Neurogastroenterology & Motility 2020: \00e14031
[xxxiii] Eccles J, et al. Neurovisceral phenotypes in the expression of psychiatric symptoms. Frontiers in Neuroscience Feb 2025 Volume 9 Article 4 pg 1
[xxxiv] Ibid.
[xxxv] Ibid.
[xxxvi] bid.
[xxxvii] https://www.mayoclinic.org/diseases-conditions/median-arcuate-ligament-syndrome-mals/symptoms-causes/syc-20505001
[xxxviii] Garland EM, Celedonio JE, Raj SR. Postural Tachycardia Syndrome: Beyond Orthostatic Intolerance. Curr Neurol Neurosci Rep. 2015;15(9):60. doi:10.1007/s11910-015-0583-8
[xxxix] Staud R. Autonomic dysfunction in fibromyalgia syndrome: postural orthostatic tachycardia. Curr Rheumatol Rep. 2008;10(6):463-466. doi:10.1007/s11926-008-0076-8
[xl] Blitshteyn S. Whitelaw S. Postural orthostatic tachycardia syndrome (POTS) and other autonomic disorders after Covid
-19 infections: a case series of 20 patients. Immunologic Research 30th March 2021
[xli] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[xlii] Eccles J, et al. Neurovisceral phenotypes in the expression of psychiatric symptoms. Frontiers in Neuroscience Feb 2025 Volume 9 Article 4 pg 1
[xliii] Self-Report Orthostatic Grading Scale Mayo Clin. Proc. 2005; 80 (3): 330-334
[xliv] Rowe P. General information brochure on orthostatic intolerance and its treatment. March 2014. Accessed March 2021. https://www.dysautonomiainternational.org/pdf/RoweOIsummary.pdf
[xlv] Raj SR. The Postural Tachycardia Syndrome (POTS): pathophysiology, diagnosis & management. Indian Pacing Electrophysiol J. 2006;6(2):84-99. Published 2006 Apr 1.
