Why do we experience head rushes?

Question

Can someone please explain exactly why we experience "head rushes" or orthostatic hypotension? I understand it is a sudden rush of blood to the brain but can someone please explain it in depth? Wikipedia fails.

Thanks!

Answer 1

Actually, orthostatic hypotension is not a sudden rush of blood to the brain...It is quite the opposite of that really. It is an excessive decrease in blood pressure and results in reduced blood flow to the brain and can cause dizziness or even fainting......When we stand up suddenly, gravity causes about a pint of blood to pool in the veins in our legs and lower body and the amount of blood returned to the heart and pumped out by the heart is reduced and your blood pressure drops. Normally your body will quickly respond to that drop in blood pressure by increasing your heart rate to compensate...........I am a charge nurse and my job is to go out and set up and run mobile blood drives at businesses, churches, and high schools... Most of our donors, the vast majority do just fine, but once in a while our donors have what we call a "reaction" to donating...Sometimes they feel funny, sometimes, they get hot and flushed, sometimes they feel dizzy,  sometimes they feel sick and sometimes they will pass out.. It is most likely to occur in first time donors....their fears of the unknown, fear of needles, fear of pain, combined with a loss of blood volume, can cause a reaction........We are trained to take care of them when this happens of course...Mostly, we try to relax them and talk with them to take away their worries and concerns and answer their questions before we start and for alot of people that works very very well...but, if a donor does have a reaction, it is the same basic thing that you are talking about here....We are taking a pint of blood from them, which reduces their volume circulating, which drops their blood pressure slightly, which can induce that orthostatic hypotension... What we do to help them is to lay them flat on the bed, with their knees bent, have them do some coughs which will get their circulation going again..give them ice packs to cool them off, and  give them something to drink.....It is a very self-limiting reaction and donors usually feel better fairly quickly.....Well, I hope I helped you understand just a little bit about orthostatic hypotension..... and maybe you learned something new as well....