YOUR HEALTH - MEDICINE 101

BLOOD LETTING
Does the very thought of having your blood drawn make you feel queasy and weak in the knees?

Imagine if you'd lived a hundred years ago. The patient’s veins were cut open with an instrument such as this – called a scareifier – and the blood would drip out until the patient collapsed!

Ancient physicians believed that illness was caused by evil spirits. And those spirits circulated in the blood. So, drain the blood from patients and you'd drain the illness as well. That was the theory behind blood letting and it was practiced well up into the 20th century.

We still do a bit of blood letting these days .. although now we use it for diagnostic tests.

To draw blood we first apply a tourniquet to the arm. The word comes from the French “to turn” and the soft rubber band stops flow in the veins, making them fuller and easier to puncture. Then we clean the skin with alcohol so bacteria doesn't get inside with the needle.

The needle is designed to be as painless as possible - honest! It has a bevel or angled part that makes it easier to insert. They're hollow and connected to a tube or syringe for collection of the blood. Though there is some pressure in veins, it is usually not enough to push the viscous blood through the thin opening in the needle. So the technician draws back on the syringe creating a negative pressure in the tube and allowing the blood to flow. When the tube is full, the needle is removed and - here's the miraculous part - your body seals the hole!

When the needle punctures the wall of the vein your body senses this and activates platelets to close the hole. Platelets are small pieces of clotting cells that are present all the time in blood. Usually they’re inactive – just along for the ride – but when they sense that an artery or vein is punctured or torn, they come alive, clumping together in a sticky mat that closes the hole. At the same time the muscle around the wall of the blood vessel contracts so that the flow of blood decreases and doesn't flush away the platelet plug. Next, a complicated chemical system known as the coagulation cascade lays down a tough woven mat of a chemical called fibrin. That seals the hole even further.

How can you help this process? First of all have a seat or lie down. Just the thought of it in some people causes your heart rate and blood pressure to fall – and so will you if you're not careful.

Also, hold the puncture site firmly for a good five minutes – longer if you are on anticoagulants or blood thinners. This pressure helps decrease the flow and allows the platelets to stick. Otherwise you bleed outside the vessel – and that can be quite painful. Ice works in the same manner. In addition don’t increase the pressure of blood in the veins – by taking blood pressure above the site, or exercising with the arm.

Next time you have to have your blood taken why not focus on this fascinating physiology – who knows, maybe then you won’t faint!