With rising, a fall in blood pressure
Some people experience drops in blood pressure when they stand up. Falls are a risk. But there are often simple ways to counter the problem.
When we stand up, blood tends to pool in the lower half of our bodies, filling veins in the liver, intestines, and other abdominal organs, as well as those in the legs. The downward flow means there's a danger of not enough blood reaching the brain, which can lead to a loss of consciousness. But adjustments occur that keep that from happening. Sensors in the aorta in the torso and in the carotid arteries in the neck trigger a response that revs up the "fight-or-flight" part of the nervous system and dials down the "rest-and-digest" part. The heart beats a little faster and stronger. Blood vessels constrict, squeezing blood into a tighter space. Blood flow and blood pressure stay more or less normal.
But with age and some diseases, these compensations for gravity's effect on blood circulation may falter. The heart gets stiffer and weaker, so it doesn't pump as well. Blood vessels get stiffer and less responsive. The sensors in the aorta and carotids become less sensitive, and the signals they send to the nervous system, less effective. As a result, some people experience sizable drops in blood pressure when they stand up, a condition known as orthostatic hypotension or, sometimes, postural hypotension. Hypo is Greek for under, and tension refers to blood pressure.