from: Postural Orthostatic Tachycardia Syndrome

POTS: An overview

Standing up is something most of us take for granted; we've been doing it since childhood. Our bodies automatically adjust to the pull of gravity by increasing vascular tone, heart rate and cardiac output. Blood vessels contract, heart rates increase and our systolic blood pressure remains the same or decreases slightly while diastolic pressure increases slightly (Brunner & Suddarth, 2000, p. 546). Our bodies operate in perfect homeostasis and we stand up with little effort.

However, the simple act of standing up can be a challenge for some people. There are disorders that affect the bodies ability to appropriately adjust to the pull of gravity. These disorders are referred to as orthostatic intolerance. Postural orthostatic tachycardia syndrome (POTS) is one of these disorders.

Postural orthostatic tachycardia syndrome is defined by excessive heart rate increments upon upright posture. A person with POTS will experience heart rates that increase 30 beats or more per minute upon standing and/or increase to 120 beats or more per minute upon standing (Grubb, 2000). These exaggerated heart rate increases usually occur within 10 minutes of rising.

While the hallmark of this disorder is an excessive heart rate increment upon standing, patients often exhibit numerous symptoms of autonomic nervous system dysfunction. It is the autonomic nervous system (ANS) that regulates the needed adjustments in vascular tone, heart rate and blood pressure upon standing. The ANS is also responsible for regulating a multitude of other organs and functions throughout the body. Some of these functions include temperature, pupil dilation and constriction, salivation and the digestive tract. A patient experiencing ANS dysfunction may experience abnormalities in the many organs and functions the ANS regulates.

Patients can be affected by different varieties of POTS. The distinct varieties may have numerous causes. Patients with the hyperadrenergic variety are affected by excessive sympathetic activity that is not turned off appropriately by the baroreflex (Grubb, 2000). These patients often have high serum catecholamine levels, decreased norepinephrine clearance, and resistance to the norepinephrine releasing effect of tyramine. They also experience more migraines, cold and sweaty extremities and have an excessive response to isoproterenol.

Those said to have partial dysautonomia have a system trying to compensate for a lack of venous constriction through excessive catecholamine output (Grubb. 2000).

Some physicians also believe there is a brain stem dysregulation form of POTS that may lead to total autonomic failure (Grubb, 2000).

Regardless of variety, POTS patients generally fit into one of four categories upon becoming ill: constitutional, post-viral, postpartum and those whose symptoms became noticeable after their body was exposed to a severe stressor (Grubb, 2000).

Constitutional patients have been sick all their lives. Post-viral patients developed POTS after an illness believed to be viral in nature. Postpartum patients developed POTS after giving birth. Most of the remaining patients developed POTS after being exposed to bodily stressors, such as surgery, trauma or chemotherapy.

Regardless of category, POTS is a chronic illness that can be debilitating at times. POTS patients use about three times more energy to stand than a healthy person (Grubb, 2002). It is as if these patients are running in place all the time. Research shows that POTS patients' quality of life is similar to those with congestive heart failure and chronic obstructive pulmonary disease (Benrud-Larson, Dewar, Sandroni, Rummans, Haythornthwaite & Low, 2002) Most patients will have to make some lifestyle adjustments to cope with this disorder.

It was once estimated that nearly 500,000 Americans had some form of orthostatic intolerance, which made standing up a challenge (Robertson, 1999). However, with research advances and growing physician education the number of patients found to have POTS symptoms is steadily rising.

POTS patients tend to be between the ages of 15 and 50 (Grubb & McMann, 2001, p. 65). Women are 5 times more likely to develop POTS than men (Grubb & McMann, 2001, p. 65). POTS does run in some families. The onset can be sudden or gradual. The quantity and severity of symptoms varies from day to day.

POTS symptoms are sometimes correctable if an underlying cause is discovered. Researchers are attempting to identify and treat the mechanisms and causes of POTS. Research shows that most patients will eventually be able to stand up with fewer symptoms (Low, 2000). Most POTS patients can look forward to experiencing improvement with proper treatment.

from: POTS Defined

Upright posture is a fundamental human activity requiring rapid and effective circulatory and neurologic compensations in order to maintain blood pressure and consciousness. The orthostatic tachycardia syndrome is a disabling disease state described at least since 1940 and is the most common reason for referral for chronic orthostatic intolerance. Patients are often unable to hold jobs or attend schools. Yet, our understanding of its pathophysiology remains incomplete. An operational definition of the syndrome (often denoted by the acronym POTS for postural orthostatic tachycardia syndrome) includes symptoms of orthostatic intolerance associated with an increase in heart rate from the supine to upright position of more than 30 beats per minute or to a heart rate greater than 120 beats per minute within 10 minutes of head-up tilt (HUT). An exaggerated increase in heart rate, often accompanied by hypotension in association with dizziness, nausea, palpitations, heat and fatigue in the upright position has been described under other names including the hyperadrenergic syndrome of Streeten, idiopathic hypovolemia of Fouad et al, and most recently the postural orthostatic syndrome of Low et al. POTS is common, affecting an undisclosed number of patients mostly in the age range of 12 to 50 years, mostly female (approximately 80%), often with onset following a viral infection or other inflammatory condition. There is an as yet undetermined but increasing apparent prevalence in children and adolescents. Resting tachycardia is common. Symptoms of anxiety may proliferate and appear to be autonomically mediated in many cases; there is also overlap with anxiety/panic disorder.


POTS has been proposed as a mechanism for symptoms of the Chronic Fatigue Syndrome in a series of adult patients. POTS and CFS may share a common pathophysiology particularly in the young . Recently, a review of patients with delayed orthostatic hypotension (delayed POTS) demonstrated a high degree of association with chronic fatigue. Our preliminary data have shown that POTS physiology underlies orthostatic intolerance in the large majority of adolescents with the chronic fatigue syndrome (CFS). In those patients we demonstrated loss of heart rate variability consistent with vagal withdrawal, increased blood pressure variability consistent with enhanced modulation of sympathetic tone, and impaired baroreflex with a phase shift causing wide blood pressure swings uncompensated by compensatory HR changes. Preliminary vascular data suggest that these autonomic findings are associated with changes in arterial and venous properties of the lower limbs during orthostasis causing fluid collection in excess of ordinary "pooling" observed in control patients.

Pathophysiology of POTS

Pooling in the lower body due to gravity is believed to cause the findings. Indeed pooling changes were found in early work and may be quite striking. Maneuvers to increase effective blood volume such as acute saline loading and lower body compression with pressure suits will reverse symptoms and signs temporarily.

The literature contains a number of potential explanations for abnormal venous pooling and fluid collection in POTS including impaired innervation of the veins or in their response to sympathetic stimulation. One such explanation favors an autonomic neuropathy that predominantly affects the lower extremities. Alpha1-adrenergic denervation hypersensitivity results. A second explanation invokes decreased alpha1- receptor sensitivity; a third, beta 1-receptor supersensitivity, a fourth altered venoconstriction, while a fifth suggests increased capillary filtration as an explanation. However, alpha 1-adrenergic control of venous filling in response to baroreflex stimulation during orthostasis is important only in skin and splanchnic circulations in humans while involvement of skeletal muscle alpha 1-receptors remain controversial. Beta-adrenergic effects may also alter venous filling, but only indirectly through arterial vasoactivity and this mechanism may be most important during exogenous beta-agonist administration (isoproterenol) or during endogenous epinephrine release later during HUT. It is uncertain how important active venoconstriction is to the orthostatic response. Finally, venous capacitance properties in POTS could be abnormal because of altered vascular structure, altered muscle tone or both.

We noted a high incidence of acral findings in CFS and POTS patients during HUT. Patients had swelling of the dependent lower extremities with purplish discoloration of the dorsum of the foot and ankle. The figure shows early published data depicting percent change in mid-calf circumference from baseline prior to tilt until the end of tilt just prior to being placed supine. The data suggest a significantly greater percent increase in circumference in POTS patients compared with syncope patients or control subjects as the result of increased pooling. Clinically, there was coolness with livedo reticularis suggesting arterial malperfusion, venous dysfunction or both.

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