POTS cannot be reduced to a simple description like, “I stand up and then I faint.” There are numerous signs and symptoms associated with the syndrome.
When some combination of the following has been in place for six months or more and the correct tests have been performed, a definitive diagnosis is more likely.
- A feeling of being lightheaded upon standingwith possible heart palpitations and a “tremulous” or shaky feeling.
- Some type of visual disturbance like “seeing stars” or blurring.
- An uncomfortable feeling in the head (throbbing) and possibly in the neck.
- An inability to concentrate or think clearly. Often described as “brain fog”
- Feeling tired and experiencing weakness.
- Fainting spells, generally within 10 minutes of standing.
- Nausea or “queasiness.”
- Discomfort in the chest including being short of breath.
POTS patients often experience difficulty with associated anxiety as they become increasingly apprehensive about standing. This leads to additional symptoms including:
- Gastrointestinal upsets like constipation and bloating and/or episodes of diarrhea.
- Changes in sweating, usually increased with a sense of feeling “clammy.”
- Insomnia that exacerbates the overall problem of fatigue.
In cases with POTS-like symptoms, any or all of the following diagnostic tests may be used to arrive at an explanation for what is happening to the body, particularly within the autonomic nervous system.
Each of the following 10 diagnostic tests is routinely used to evaluate patients suffering from symptoms typically seen in POTS. All are designed to understand aspects of blood flow and nerve function as they relate to posture and other external stimuli.
Multiple tests are employed in an effort to create a complete picture of exactly what precedes an episode.
The posture study monitors heart rate, blood pressure, and the plasma concentrations that regulate them when the patient is lying down and standing. Blood is drawn from an IV in the arm during the test. The patient lies still while baseline readings are taken. The patient then stands up for 30 minutes while the measurements are repeated.
POTS patients will show an increased heart rate of 30 beats per minute when they stand and an accompanying drop in blood pressure of < 20/10 mm Hg. Some will also show elevated norepinephrine levels of > 600pg/mL.
Head Up Tilt Table
Doctors use the tilt table to evaluate cardiovascular response to positional changes. In POTS cases they are looking for a sudden drop in blood pressure with either an increase in pulse rate or fainting when the patient is upright.
To perform the test, the patient lies on the table with straps around the abdomen and legs and then is gradually tilted upright between 60-80 degrees for 45 minutes. The intended purpose is to replicate the patient’s problem in a controlled setting.
POTS patients will show an increase in heart rate of > 30 beats/minute during the head up tilt with little or no change in blood pressure, usually < 20/10 mm Hg.
A cardiac output test judges the amount of blood the heart can pump by measuring pulmonary blood flow. The patient is forced to breathe through the mouth while wearing a device containing oxygen and two inert gases. A clamp renders respiration through the nose impossible.
One of the inert gases is blood soluble, disappearing as the patient breathes in direct proportion to the rate of pulmonary blood flow. The other gas does not enter the bloodstream, therefore allowing for lung volume to also be measured.
(Note that there are other methods for measuring cardiac output. This method is, however, quite common.)
Beat-to-Beat Blood Pressure
Beat-to-beat blood pressure testing non-invasively tracks changes in response to various tests through a bracelet-like wrist device with a Velcro strap secured around one finger. This monitor is worn for the duration of any other type of testing being performed.
In the Valsalva maneuver, the patient blows against a resisting surface for several seconds followed by a period of relaxation. The action of the blowing increases pressure in the chest and abdomen, forcing blood out of the chest and down into the arms with a brief increase in blood pressure. This is referred to as Phase I.
The stroke volume, which is the amount of blood ejected by the heart with each beat, plummets due to the decreased entry of blood from the veins as a consequence of the straining. The brain senses these changes as well as the concurrent increases in nerve traffic causing more norepinephrine to be released. This tightens blood vessels throughout the body. This is Phase II.
Phase III begins when the patient relaxes, causing a brief drop in blood pressure before the blood rushes back into the chest. Blood pressure increases in Phase IV and since the blood vessels are constricted, an overshoot of blood pressure is produced, outflow falls, and with it the heart rate.
Observing these various changes and their rate and interaction gives physicians information about sympathetic and parasympathetic function. Patients with the kind of autonomic dysfunction present in POTS will likely have an exaggerated blood pressure increases in Phases II and IV.
Heart rate normally varies with the breath, increasing when we breathe in and decreasing when we breathe out. These changes, which are controlled by the parasympathetic nervous systems are called respiratory sinus arrhythmia.
In a sinus arrhythmia test, the patient’s heart rate is monitored while taking a series of deep breaths, roughly six per minute. A difference of 15 beats between minimum and maximum heart rate is considered within normal range.
Typically patients with POTS will have normal results on this test, but if abnormalities do show up, they may suggest a diagnosis of a condition other than POTS or of a condition present in conjunction with POTS.
A Transcranial Doppler test determines the velocity of cerebral blood flow. The patient is in an upright position, standing or on a tilt board. A Doppler probe placed near the temple emits high-frequency sound waves that are used to map the speed of blood flow in the cerebral vessels. In patients with POTS the expected results would be decreased velocity when in an upright position.
Cold Pressor Test
During a cold pressor test the patient plunges their hand in a tub of ice cold water and leaves it submerged for 1-2 minutes while both heart rate and blood pressure are monitored.
The normal reflexive action is an increase in heart rate and systolic blood pressure. A patient with POTS, however, will show increases in systolic and diastolic blood pressure much greater than those observed in normal individuals.
The QSART is a sweat test that gauges the ability of sympathetic nerves in the skin to release acetylcholine. If the individual has lost sympathetic nerve terminals, no sweat will be produced. If the person has a brain abnormality that inhibits sweat production as the temperature increases, they will still sweat during a QSART test. Therefore, the QSART helps to distinguish between loss of terminals and misregulation of signals sent along the sympathetic nerves.
The test is performed by wiping the leg and wrist with acetone and then alcohol. This cleans and dries the skin. Next, four electrodes are placed on three areas of the leg and one of the wrist.
The electrodes are filled with acetylcholine, which is activated with a mild electrical current to stimulate sweat gland activity while allowing the body to release its own acetylcholine causing sweating in adjacent sites. The entire procedure requires about 45 minutes.
Measuring the degree of sweating response helps doctors to determine the exact nature of sympathetic dysfunction that may be contributing to the symptoms seen in POTS.
The Endothelial Function test judges the function of the cells that line the blood vessels. A baseline blood pressure reading is taken first before an uninflated blood pressure cuff is placed on the non-dominant arm for later use. The index finger of each hand is then placed inside a plastic cylinder called an EndoPat probe, which will measure arterial tone.
Baseline readings are again taken while the patient sits still for 5 minutes, at which time the blood pressure cuff is inflated to a level greater than the systolic blood pressure for the purpose of stopping blood flow for 5 minutes. Then the cuff is deflated and additional readings taken over another 5 minute period.