Why Does My Blood Pressure Drop When I Lie Down?
The National Institutes of Health says that blood pressure is the force of blood against the walls of the arteries, blood vessels that transport blood away from the heart. Blood pressure can vary with changes in position, stress, exercise and sleep.
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Blood Pressure
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Blood pressure is recorded using two numbers -- the systolic, which is the pressure exerted by the blood when the heart contracts, over the diastolic, the pressure on the arteries when the heart is at rest.
Blood Pressure at Rest
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When lying down, the heart doesn't have to pump as hard to get blood to the upper parts of the body. When standing, the heart has to pump against gravity to get blood to the neck and head. The body compensates for the effects of gravity by increasing the heart rate and constricting blood vessels.
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Blood Pressure Increases
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Blood pressure generally increases from the laying position to the sitting position and the sitting position to the standing position. The increases are regulated by the autonomic nervous system (ANS).
Autonomic Nervous System
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The American Heart Association says the ANS is a regulatory branch of the central nervous system that helps people adapt to changes in their environment.
ANS Failure
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The ANS normally causes the blood pressure to rise upon standing but ANS failure can occur, causing blood pressure to drop upon standing. This is called orthostatic intolerance (OI) and can cause dizziness and fainting. People with OI may have higher blood pressure when lying down.
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