So, a lot of people are always surprised at the crap my body goes through during a mountaineering expedition. I remember when I had just come back from Mt. McKinley and I went to the doctor for a checkup. They made me fill out a few sheets, like this one:
I remember the doctors face when he saw that I had checked nearly everything on that sheet.
On Everest, it's even worse, for two reasons: higher elevation and more time spent at high elevation. So what does the higher elevation do? Well, simple. Most of you guys have probably been to a place that was higher in elevation (like Denver, say) and were probably really out of breath after going up a short flight of stairs. The basic reason people have a harder time breathing at higher elevation is because there is less air pressure, thus the air molecules are spread out a bit more (less air in a given volume compared to sea level). That makes it harder for our bodies to get the oxygen it needs in the same breaths we are used to taking at sea level. So, we breathe harder and more frequently to compensate.
Because at 17,000 ft (base camp of Everest) you are already at a very high altitude and because you end up "living" there for +6 weeks, your body has to do something to deal with its constant struggle for air. So, because the red blood cells in your body are what carry the oxygen around your body, these are what your body starts producing more of so that it can carry more oxygen. It's a pretty remarkable process. This is the reason why some athletes train at high altitudes. Because when they come back to sea level, they may have twice as many red blood cells giving their body oxygen, which allows their body to function much better then regular folks. Imagine sprinting and getting out of breath vs. sprinting at sea level after being at altitude for a long time. It's going to take more to get you out of breath.
One issue with your body producing more red blood cells is that it makes your blood thicker and more syrup-ier. This is bad because this means blood flow can be slow (i.e. slow circulation). When its freaking freezing on Everest, the last thing you want is poor circulation. You're blood will freeze quicker, and you'll be prone to frostbite/frostnip quicker. To deal with this issue, mountaineers are always drinking water. Tons and tons of it. Probably around 3-6 liters a day. This helps keep the fluid in your body going, and keeps your circulation flowing to the farthest extremities of your body.
Oxygen deprivation is probably the primary concern of anyone on Everest, followed by frostbite. There are obviously tons of other hazards on Everest, but there are two other big ones I should mention. One is snowblindness. This happens at high elevation where ultraviolet radiation is high (not to mention, places with snow worsen this because the snow effectively works as a mirror for radiation). It's basically having a sunburn on your cornea. Ouch. This is easily prevented by wearing UV protecting goggles/glasses. On an expedition, 90% of the time, you are wearing sunglasses. But take your glasses off for too long while climbing and your eyes will start to scratch and it will feel like you have sand in your eyes. If it gets worse, you can experience temporary blindness. Not good when your are trying to climb down a mountain....
Another tough physiological problem climbers deal with is energy consumption. Basically, how to keep your body filled with the fuel it needs to be active at high altitude. I'm expecting to lose a good 20lbs over the course of the expedition (I'm a lean guy, so that's saying a lot). On a high altitude climb where you're climbing steep terrain for many hours at a time, with heavy gear, all while your lungs are working overtime to get the air it needs, researchers have said that climbers can expend up to 6000 calories a day. THAT IS INSANE. The recommended intake of calories for men is 2000-3000. So obviously, feeding yourself is a huge deal on Everest. On an expedition, it really doesn't matter how well you eat, but rather how many calories you are shoving in your mouth. The more the merrier. This means I need to bring lots of small high calorie foods, like CANDY BARS! Basically anything with high caloric value.
What it comes down to is drinking water and eating right. Pump yourself with both of these and you are bound for positive results and hopefully a fully ready body that will take you up the mountain. Also, gaining a bit of chub before heading out on an expedition is highly recommended. As I finish this donut in my hands, I will gladly say that this is an awesome recommendation, haha.