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Friday, December 10, 2010

Cold Blood

It’s December and in northern countries like Canada, in spite of global warming, we can still count on the cold. Surprisingly however, I’ve noticed on the coldest and stormiest days that encounters with neighbors and strangers are more friendly and cheerful. I think it’s because we are all in the same boat - sharing the struggles and discomfort of our plight.

To add to discomfort it can be risky when it is bitterly cold. We’ve all heard stories of people suffering fatal heart attacks while shoveling snow or playing winter sports and the hospital statistics corroborate the stories.

In mammals like us, our body has to be kept at a remarkably constant temperature and when we are out in the cold, blood gets directed from close to the skin to our body core. Because the same amount of fluid is then in a smaller core volume, our blood pressure goes up.

If we are exerting ourselves with shoveling snow or skating, our heart rate goes up too and we need more oxygen to keep functioning so we have to breath faster. That makes things worse because the intimate contact of the cold air in our lungs tends to cool the blood and that can be dangerous! Experiments show that if our blood temperature drops, platelets in the blood tend to stick together and form clots. If the clots are big enough, they can cause a heart attack.

Let me hasten to add that only a few who exert themselves in the cold will ever have a heart attack! But those who just may have clogged arteries or high blood pressure anyway, be warned and use common sense – wear a hat [your brain is actually 80% blood by volume and you need to keep it warm] and breathe through your scarf.

I had a couple of horses one year and over wintered them in an unheated barn. Some nights were 35C below zero [around -30F] and I worried about them and started thinking about how the animals in the woods survived and why their feet didn't freeze.

It turns out that in wild creatures [birds included] the arteries delivering warm blood down the legs are intimately intertwined with the veins bringing cold blood back from the feet. The heat exchange means that there is a temperature gradient from near freezing in the foot to near body temperature at the top of the leg. Sometimes when my feet feel like they are freezing, I think of how great it would be if we humans had the same marvelous mechanism! Rie

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