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Orthostatic Hypotension

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Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

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Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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What is orthostatic hypotension?

When a person stands up from sitting or lying down, the body must work to adjust to that change in position. It is especially important for the body to push blood upward and supply the brain with oxygen. If the body fails to do this adequately, blood pressure falls, and a person may feel lightheaded or even pass out. Orthostatic hypotension is the term used to describe the fall in blood pressure when a person stands (orthostatic= upright posture of the body; hypo= less + tension=pressure).

Adequate blood supply to the body's organs depends upon three factors:

1. a heart strong enough to pump,
   
   
2. arteries and veins that are able to constrict or squeeze, and
   
   
3. enough blood and fluid within the vessels.

When the body changes position, a variety of actions occur involving all parts of the cardiovascular system as well as the autonomic nervous system that helps regulate their function.

The autonomic nervous system can be considered to "run in the background" of the body, regulating body processes that we take for granted. There is a balance between the sympathetic system (adrenergic nerves), that speed things up, and the parasympathetic system (cholinergic nerves) that slow things down. These names are based on the type of chemical that is used to transmit signals at the nerve endings.

• Adrenaline (from the sympathetic nervous system) allows the body to respond to stress. Imagine seeing a bear in the woods; your heart beats faster, your palms get sweaty, your eyes dilate, and your hair stands on end.
  
  
• Acetylcholine is the chemical that is the anti-adrenaline and is involved in the parasympathetic nervous system.

These two systems are in balance, and yet need to respond to routine changes in the body that happens throughout the day.

• When the body moves to a standing position, pressure monitors (baroreceptor cells) located in the carotid arteries and the aorta sense a subtle drop in blood pressure because of gravity, which causes blood to flow towards the legs.
  
  
• Almost immediately, the sympathetic system is stimulated, causing the heart rate to increase, the heart muscle to contract or squeeze more forcefully, and blood vessels to constrict or narrow.
  
  
• All of these actions serve to increase the blood pressure so that an adequate amount of blood can still be pumped to the brain and other organs.
  
  
• Without these changes, gravity would cause the blood to remain in the lowest part of the body and away from the brain, causing symptoms of lightheadedness or even passing out.

Orthostatic hypotension is not a disease or a complaint from an individual; it is an abnormal change in blood pressure and heart rate associated with an illness.