Originally Posted by bwana
Cold extremities are often the first sign of hypovolemia. The body needs a very specific blood volume. Every hour you lose 100 cc through your skin and breath. As you lose liquid, your blood vessels are supposed to contract to maintain blood pressure for adequate circulate. This reduces radiative warming of extremities. In addition, vascular compensation is diminished in some older folks (like me) - the vessels don't contract as much as they should, so the heart has to pump harder to maintain blood pressure. This is not symmetrical throughout the body so perfusion is still reduced in fingers and toes. Add to that the presence of diseases like Raynaud's, etc, then peripheral perfusion can suffer greatly. Bottom line, hydrate aggressively on the morning of skiing - at least 1 liter before you go out. And remember, caffeine is a diuretic so a couple of cups of coffee will encourage a pit stop by 1030. This is life. There is no magic solution.
Your vascular system actually has an enormous ability to accommodate changes in blood volume without changes in cardiac output, skin perfusion, cardiac work, or blood pressure. The venules--the microscopic vessels on the venous side of the capillaries--act as a reservoir where most of the blood in the body is located at any given instant. These muscular vessels can expand and contract with changes in blood volume in order to keep the filling pressure of the heart constant. Arteriolar diameter and skin perfusion are not affected until volume loss is so severe that the venous reservoir can no longer compensate. In addition, as we dehydrate our blood recruits fluid from the tissues--interstitial fluid--fluid which has to be replenished at some point or muscle function will suffer. The kind of hypovolemia that would result in decreased circulation and cold extremities is the kind that results from serious trauma or prolonged fluid deprivation during serious exercise. As far as drinking a liter or more before you go out--unless you started the day very dehydrated most of that liter will wind up in your bladder. The effect on your cold fingers will depend on whether you go inside to pee or take off your gloves to pee in the woods.
The point about caffeine being a diuretic is a good one. Alcohol is a diuretic as well, as most of us know, some more than others. (It also dilates skin blood vessels, which warms the hands but can reduce core temperature.) And diamox, if you take it to deal with altitude, is a stronger diuretic than either. The problem with any diuretic is that not only do you dehydrate but you lose the best sign to tell you you're dehydrated--sparse, dark urine. I'm all for staying hydrated but I think it has been overemphasized in recent years--witness the occasional ultra-distance athlete dying of water poisoning (hyponatremia--low salt level in the blood due to dilution by water.)
Edited by oldgoat - 2/17/15 at 10:32pm