When humans stood upright for the first time s/he faced physical challenges four legged animals did not have to deal with. Assuming an upright posture resulted in positioning of the heart much higher than the legs and the brain even higher. This upright posture presented the circulatory system with new physiological challenges. The circulatory system had to figure out how to move blood from the legs against gravity all the way up to the all-important brain. When the body is upright, both during standing and walking, the circulatory system is most stressed. How can the body move blood up the legs against gravity? Returning blood from the legs back to the heart is a challenge even among normal individuals. Returning blood from the legs back to the brain is an even greater challenge.
Rather than having diseased organs, POTS represents autonomic dysfunction, failure of several of the automatic bodily functions that are responsible for maintaining upward circulation of blood while upright. POTS can best be compared to an adolescent with a newly acquired body (tall structure) that has grown quickly … but, the building’s electrical wiring system (automatic functions) has not yet matured fully and is not functioning properly. Normal complex biologic processes (automatic bodily functions) have the responsibility to return blood from the lower body to critical organs like the heart and brain. When not functioning properly, as occurs in POTS patients, excessive blood accumulates in the lower abdomen and lower limbs rather than immediately returning to the heart to recirculate. What’s required is a reliable nervous system that is able to automatically and immediately respond to this relative volume shift – step-in and initiate mechanisms to increase heart rate, vascular tone and ultimately cardiac output.
POTS is characterized by rapid heartbeat when standing upright. The primary symptom complex consists of orthostatic (standing upright) intolerance, the body’s difficulty adjusting to the upright position. Rapid heart rate occurs upon assuming an up-right posture or standing position and reverses slowly when sitting or reclining. Additional criteria required to establish the diagnosis of POTS include the presence of symptoms related to gravitational shifting of blood to the lower body, decreased cardiac output and sympathetic nervous over-reactivity. Practically all of the bizarre symptoms experienced by patients with POTS are directly related to this diminished blood supply to the heart and brain. Among the most common symptoms are fatigue, headaches, light-headedness, eye and abdominal disturbances. Symptoms may be constant or fluctuate from day to day or week to week. To establish this diagnosis, symptoms usually occur daily and need to have been present for at least 6 months.