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Orthostatic Hypotension (Low Blood Pressure When Standing)

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Orthostatic hypotension definition and facts

  • The autonomic nervous system makes changes in blood pressure and heart rate to allow the body to provide adequate blood supply to the brain when the body changes position.
  • Symptoms of orthostatic hypotension include lightheadedness, weakness, blurred vision, and syncope or passing out.
  • Dehydration, blood loss, and anemia are the most common reasons to develop low blood pressure when standing.
  • Beta blockers, other high blood pressure medications, and medications such as sildenafil (Viagra) may all cause orthostatic hypotension.
  • Vasovagal syncope may cause symptoms of fainting when the vagus nerve is stimulated by a noxious stimulus, either physical (pain) or emotional.
  • Diagnosis is often made by history and physical examination. Injury from falling is the main complication of this entity.
  • Maintaining adequate hydration is the best way to prevent orthostatic hypotension if the hypotension is caused by dehydration. However, overhydration can exacerbate congestive heart failure. Patients with CHF and orthostatic hypotension need to closely monitor fluid intake and make changes only with physician supervision.

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.

Medically Reviewed by a Doctor on 1/13/2017


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