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.
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.
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:
a heart strong enough to pump,
arteries and veins that are able
to constrict or squeeze, and
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.
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.
Author: Richard Weil, MEd, CDE
Medical Editor: Jay W. Marks, MD
Viewer Question: I sometimes feel dizzy while doing some yoga stretches where the head is lower than the heart (like downward facing dog). What types of exercise should you avoid when you have
low blood pressure?
Fitness Expert's Response: The medical term for your condition is
orthostatic hypotension. It typically occurs in situations like you are describing when there is a sudden change in posture, particularly so when the head rises from below the heart, but it can also happen from a supine or prone position when the head is level with the heart. The reason it happens is that circulation (blood pressure) isn't forceful enough to return adequate blood to the brain and so there is a moment of dizziness. The danger is that you can pass out, and so you need to take precautions to avoid the problem.
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