|MadSci Network: Anatomy|
The short answer is that your neurovascular system over-responded with an event known as a vaso vagal response. That is what I assume based on what you tell me. What did your doctor tell you? I have the same thing happen. It usually starts with an event such as yours. A person fasts, gets volume depleted, the body is in the survival mode - heightened neurovascular tone, etc. A needle is stuck into the skin, perhaps not the smoothest stick, It hits the vein, the vein collapses or constricts (being in survival mode - can't afford to lose any thing, especially blood). The phlebotomist keeps trying to get blood, pain is experienced somewhere along the line, a combination of above triggers a response from the Vagus nerve or it's offshoots and there is momentary vaso dilitation and the pulse drops (effects of the Vagus on the heart and vessels). This results in a loss of pressure through the system. I imagine you were sitting up in a chair. The brain is above the heart in this position and detects the drop - this is where you begin to gray out. Somw people actually lose consciousness momentarily - the brain goes to 'GENERAL QUARTERS' sending out a flurry of messages all over the place - resulting in a massive surge of adrenalin to vasoconstrict the vessels, increasing resistance again in the system and accelerate the heart. This is usually where most people get sick to their stomachs. I would have them draw the blood while you are lying down on a table. Afterwards, don't just jump up, wait a few, to let the system recallibrate. If you are flat, and the first part happens, you will not know it as your head is at the same level as your heart. Thus, if you 'vagal out' the system is still perfusing the 'squash' (brain). Therefore, the horrible pendulum effect of grayout/blackout followed by intense nausea and cold clammy sweat is avoided. I always have my guys drink plenty of water when they are fasting. Fasting results in a greater consumption of intracelluar water due to needs of the body. It feeds off of stores held in the liver, and requires extra water for this plus other metabolic processes. Bottom line - lay flat when they draw your blood. You can pretty much count on not having that experience again if you are flat. If you are standing or sitting it will probably reoccur. Why? This is anecdotal, meaning everyone I have talked to has had this reoccur once it starts - varying degrees of wooziness - I have not read a study that looked at it - there may be one out there. I think that some kind of neuro vascular pain mediated cycle gets set up, this includes the apprehension due to the last experience. I know that I was fine until I had a flight physical one day in Okinawa. Fasting, went on a 3 mile run just prior, had to really work to urinate a sample for them which was very dark (warning sign of low body water) and the corpsman stuck me a number of times - fortuantely the msater chief was walking by and saw my skin color go deathly pale and got me down on the ground before I got there on my own. Hope this helps. When I give blood, whether for donating or testing, I lay flat and avoid the whole unpleasant experience. Don't let anyone tease you or give you grief about this. It is not a reflection on your manhood or manliness, it is totally involuntary and involves that part of the nervous system that we do not consciously control.
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