heart and blood vessel disorders
Low Blood Pressure
Changing the body's position
Blood pressure can vary throughout the body due to the direct action of gravity. When a person is standing, blood pressure is higher in the legs than in the head, much in the way that the water pressure at the bottom of a swimming pool is higher than that at the top. When a person lies down, blood pressure tends to be more equal throughout the body. When a person stands up, blood from the veins in the legs has a harder time getting back to the heart. As a result, the heart has less blood to pump out, and blood pressure may temporarily drop throughout the body. When a person sits down or lies down, blood can more easily return to the heart, and cardiac output and blood pressure may increase. Elevating the legs above the level of the heart can increase return of blood to the heart, which increases cardiac output and raises blood pressure. 