More on POTS from: http://home.att.net/~potsweb/POTS.html

Tachycardia means an extremely rapid heart rate, usually signified by a pulse rate of over 100 beats per minute (bpm).  Postural Orthostatic Tachycardia Syndrome (POTS) is clinically defined as a heart rate increase of 30 bpm or more from the supine (laying down) to the standing position within ten minutes or less.  Patients with florid POTS develop tachycardia over 120 bpm within 5 minutes or less.  Studies show that about 75% of POTS patients are women and that a genetic tendency to develop POTS is usually transferred from mother to daughter. 

The brain is the most metabolically active organ in the body and requires a steady supply of oxygen and glucose to maintain healthy function.  Although the brain represents only 1-2% of the body's mass, it utilizes 20% of the body's oxygen consumption and 15% of cardiac output.  Our brains are thus highly dependent on adequate blood circulation to maintain our sense of health and well being.  The thought process, regulation of body temperature, hormone release, and many autonomic systems can be impaired by loss of proper blood pressure control.  Our survival is as dependent on adequate blood pressure regulation as on the fundamental process of breathing.   

Chronic Fatigue Syndrome (CFS), also known as Chronic Fatigue Immune Dysfunction Syndrome (CFIDS), is somewhat related to POTS, at least in terms of a similarity of many of the secondary symptoms.  In Europe CFS is called myalgic encephalomyelitis (ME).  Doctors at Johns Hopkins, Vanderbilt University, the Mayo Clinic, and the Medical College of Ohio believe that the blood pressure abnormalities mentioned in this paper, known together as orthostatic intolerance, are a cause of some of the symptoms of CFS.  It is estimated that 800,000 Americans have CFS and approximately 100,000 Americans have POTS. Some percentage of patents have both POTS and CFS.

POTS can be caused by genetically inherited neurotransmitter disorders, including disorders of catecholamine production and release, such as Norepinephrine-Transporter Deficiency.

Symptoms  POTS is defined as a minimum 30 bpm acceleration of heart rate from the supine to the standing position within 10 minutes or less, with a peak heart rate reaching at least 120 bpm.  Some patients have heart rates that go all the way up to 150 bpm and beyond.  During tilt table testing, some POTS patients have large drops in blood pressure and pass out (syncope), while other patients have only relatively shallow drops in blood pressure.  A small percentage of POTS patients have no drop in blood pressure at all. 

POTS is diagnosed on the basis of heart rate increase and heart waveform signature revealed by electrocardiogram, not on the basis of a drop in blood pressure, as is the case with orthostatic hypotension and neurally mediated hypotension (NMH).  Neurally mediated hypotension is commonly associated with POTS, but having NMH is not a prerequisite for a diagnosis of POTS.  The secondary symptoms of POTS vary significantly from case to case.  The most commonly reported symptoms are listed below.    

The length of time POTS patients can comfortably stand varies widely from case to case.  Patients may become dizzy, lightheaded, and develop chest and heart pain from standing beyond their limit.  Blood pooling in the legs and splanchnic bed (abdomen) may occur, which is felt in the same way you feel water fills your mouth when you get a drink.  Shortness of breath, blurry vision, tingling in the legs, sweating, and feelings of heat from increased adrenaline production are common symptoms of orthostatic stress.  Some patients pass out frequently, which is dangerous as well as uncomfortable.  Many patients experience spells of supine or standing vertigo, but this symptom is dependent on the root cause of the POTS.  Remember that POTS itself in not a specific disease like polio, but rather a symptom and a syndrome (a collection of symptoms).

The current prevailing theory is that the heart pain associated with POTS is predominately non-ischemic, but further research may alter this perception.  It is believed the left sided heart pain so common among POTS sufferers is due to differences in heart chamber pressures, abnormal heart wall motions, and/or nerve damage.  It is not related to common angina which is usually caused by blocked arteries cutting off the supply of blood to the heart.  While uncomfortable and debilitating, this left sided heart pain is not believed to be immediately life threatening.  On occasion, patients may also have the strange sensation that their lungs are filled with glue.  This uncomfortable feeling is often misinterpreted as being evidence of a lung infection, while in most cases it is a cardiovascular symptom.   

With POTS and NMH you become lightheaded and weak even before you get a measured crash in blood pressure because the small blood vessels in the brain paradoxically constrict when you are under orthostatic stress.  This cerebral vasoconstriction cuts off the blood supply to brain cells while veins in the legs and splanchnic bed are dilated and pooling blood away from your heart. With inadequate filling of the heart's left ventricle and abnormal function of the alpha and beta adrenergic systems, it is no wonder that strange and irregular heart beats (palpitations) are a universal symptom of POTS.  These are often referred to as ectopic heartbeats, with frequent premature heartbeats the most common aberration reported. 

POTS often generates a temporary rise in blood pressure immediately upon standing due to the rapid acceleration of heart rate.  Tachycardia is the body’s defense mechanism against a lack of sufficient venous blood returned to the heart.  Blood vessels, particularly veins, can become unnaturally dilated, causing blood pooling in the legs and splanchnic bed (abdomen).  Thus the heart must beat more times in a minute to make up for the reduced blood volume transferred by each beat.  If a POTS patient stands up too suddenly, there may be so little blood in the heart that it may collapse upon itself, causing very painful heartbeats.  Patients often have measurably low standing pulse pressure, which can be an indicator of venous pooling.

Frequent urination is a common symptom of POTS, NMH, and severe cases of CFS.  This problem is sometimes misdiagnosed as diabetes insipidus, which is a disease caused by reduced production of a pituitary hormone called vasopressin.  Some POTS patients develop a diabetes insipidus like syndrome which is believed to be caused by somewhat reduced vasopressin output, low blood volume, and disruption of the alpha adrenergic system, which helps the kidneys retain water and sodium.

Reactive hypoglycemia is a common problem for both POTS and CFS patients, and occurs through a complex series of neural and hormonal interactions which are not yet fully understood.  The traditional definition of hypoglycemia is an abnormal lowering of blood sugar levels after the body overreacts to carbohydrates with excessive insulin production.  Researchers now understand that this lowering of blood sugar levels is not the only cause of symptoms.  Recent studies show that when patients with reactive hypoglycemia eat carbohydrates, which cause a sudden increase in blood glucose levels, their bodies abnormally produce excessive amounts of adrenaline and other stress hormones.  These stress hormones themselves cause many negative symptoms of their own, in addition to the eventual crash in blood glucose levels due to excessive reactive insulin production.   

Most patients with POTS have difficulty sleeping, which may result from a number of factors, including abnormally high adrenaline levels caused by increased orthostatic stress (the stress of standing).  Central sleep apnea is a common problem for people with POTS, which in some cases may be due to damage to the medulla, which controls important cardiac and respiratory functions.  Central sleep apnea causes breathing to temporarily stop while sleeping.

Low grade fevers, mild chills, and general flu like symptoms are common with POTS.  This may be explained by a neurologically based loss of control of basic autonomic regulatory systems, an overactive immune system, or  abnormally high adrenaline levels effecting body heat production. Many patients have positive anti-nuclear antibody tests (ANA test), which some doctors say is due to high adrenaline levels activating the immune system.  Other doctors suggest positive ANA tests may be due to an autoimmune disorder damaging nerve cells.  Patients are left in confusion as to which theory to believe.

Chronic fatigue and weakness are common problems for POTS sufferers.  Those who have pure POTS, without CFS or significant immune system involvement, generally feel better and have greater postural tolerance despite tachycardia.  Many POTS patients have common allergies, uncommon food allergies, and are highly drug and chemical sensitive.  Many POTS and CFS patients experience severe night sweats.

Nausea, bloating, and sore intestines are a frequent complaint.  The nausea can usually be eliminated by not stressing yourself beyond your capabilities.  Bloating is caused by low motility in the intestines, a byproduct of nerve damage.  Patients often develop irritable bowel syndrome, which leaves the intestines feeling raw and tender.  Difficulty swallowing (dysphagia - pronounced dis-FAY-jee-uh) is also a frequently reported problem.

Numbness in palms and soles is a common symptom of POTS.  Legs, arms, and hands are often totally numb upon awakening from sleep.  Upper extremity somatosensory evoked potential studies are usually normal in POTS and CFS patients, but this is not always the case.  Unusual coldness of the hands is also common and is referred to as acral coldness.  Patients frequently experience sporadic itchiness, burning and tingling sensations all over the body, especially at night.  Some patients may also have dramatically reduced sweating, which can be tested for through a thermoregulatory sweat test. 

Most POTS patients have poor balance, which may be caused by decreased blood flow to the brain and other disturbances in the vestibular system.  The patent's root neurological damage may also cause balance problems directly as well as causing the debilitating symptom of orthostatic intolerance.  Patients are often unable to pass a drunk test by walking with one foot placed directly in front of the other.  An abnormal gait is common.  Patients may walk with legs wide apart and feet flared out to the sides as an instinctive adaptive response to increase their stability.      

Eye pain is another common problem, as is a feeling of pressure behind the eyes.  Patients can become so weak that their eye muscles are easily strained and focusing is difficult.  Many POTS and CFS patients see tiny little black dots floating in front of their eyes.  This is a problem of the fluid in the eyes which occurs naturally with age, but which can be made dramatically worse by the onset of CFS or POTS.  

Supine blood pressure readings are usually normal or below normal in POTS patients.  This is in sharp contrast to multiple system atrophy (Shy-Drager syndrome), idiopathic orthostatic hypotension (Bradbury-Eggleston syndrome), and other forms of central autonomic failure typified by low standing blood pressure and high supine blood pressure.  Lack of supine hypertension (high blood pressure when lying down) is usually a sign you do not suffer from the classic forms of central autonomic failure.

Most POTS patients will only have a few of the symptoms listed here, while others will have unique symptoms all their own.  A poor memory is a major symptom of POTS, and many patients will have a difficult time just remembering their own symptoms while conversing with doctors.  The total damage to the autonomic nervous system POTS sufferers experience, called dysautonomia, causes what Dr. David Robertson of Vanderbilt University refers to as “mild autonomic abnormalities.”  These symptoms, such as frequent urination and reactive hypoglycemia, are not life threatening, but they are quality of life destroying.

People who do not have problems with low blood pressure have a difficult time understanding the concept of orthostatic stress.  They fail to realize that blood pressure is as basic and essential a bodily function as breathing.  How would you feel if your breathing were constricted for even one minute?  Low blood pressure can cause an enormous amount of symptoms and suffering, but those who don’t have it often miss that fundamental point.  Some patients with POTS have such a damaged regulatory system that they may get paradoxical wild swings in blood pressure from below 50 to over 200.  Complexly, POTS can be a low and high blood pressure problem combined.