Science at Altitude:
Sports Authority Field at Mile High is exactly that -- at a Mile High, 5280 feet above sea level. High altitude means two things in terms of oxygen and decreased air pressure:
1. Less oxygen molecules
2. Less air pressure to help push air into our lungs when we breathe
These two factors cause hypoxia (no or low oxygen getting to the cells in your body). Why is oxygen so important? Oxygen is a key factor in how our cells make energy. When cells have oxygen and glucose (sugar) a reaction occurs that makes energy (in the form of ATP, the body's energy currency) and has the byproducts of water and carbon dioxide.
So without oxygen, our bodies can't make energy efficiently and our cells, tissue and eventually organs can stop working. This is what happened to Ryan Clark last time he played at Mile High, except his situation is even more complicated, because of having sickle cell. But let's look at what the body normally does, and then we'll take a closer look at sickle cell at high altitude.
For folks coming in from sea level, like the Pittsburg Steelers for the 2011 playoff game against the Broncos, there are two stages of adaptation the body must go through to ensure oxygen levels stay topped off within the body:
1. Short term adaptation: The body immediately starts to concentrate red blood cells (which contain hemoglobin, the molecule that carries oxygen) by filtering out liquid from the blood. This is why when you first come to high altitude you will have to go to the bathroom more and part of the reason why dehydration can be such an issue.
2. Long term adaptation: The kidneys immediately start sending chemical signals (erythropoietin) to the bone marrow to get them to make more red blood cells (and therefore more hemoglobin molecule in the red blood cells to carry oxygen). Over a period of time (anywhere from a few days to a couple weeks) a person will have topped off their red blood cells.
In the case of Ryan Clark and folks with sickle cell, this process is complicated. Your DNA is like a cookbook for your body. Each recipe in the DNA cookbook is a gene, and tells your body how to make one important thing your body needs. People with sickle cell disease have a change to the recipe/gene that tells the body how to make hemoglobin. Since hemoglobin is located in red blood cells, the molecule affects the shape of these cells. Normal hemoglobin allows red blood cells to be circular; with sickle cell the shape of the red blood cells is more crescent-shaped. The sickle cell crescent-shaped red blood cells can clog up blood flow, restricting the ability for the blood to deliver oxygen to cells around the body.
This is a genetic disease. Since you get one copy of each gene from mom and one from dad, a person can have two mutated copies, or sometimes might only get one mutated copy. With two mutated copies of the gene/recipe, the disease is more grave then having only one copy of the mutated gene because all the hemoglobin the body makes is from the mutated recipe, so all red blood cells are crescent-shaped, increasing the chances that blood flow will be restricted. My understanding is that Ryan Clark has only one mutated gene/recipe for making hemoglobin (he got one normal gene from one parent and one mutated one from his other parent), and so for the most part he is asymptomatic under normal conditions.
At high altitude however, your body is concentrating red blood cells. For folks with sickle cell, this means the body is increasing the number of sickle cell red blood cells in the same amount of liquid. This dramatically increases the chance that the sickle cell crescent-shaped red blood cells will clog up the arteries and therefore restrict blood flow, causing cell death, and organ failure.
Your body is a complicated and fascinating thing, and the more we understand about how genes/recipes work, and how the body reads and makes things from recipes (gene expression) the more we will understand both health and disease.
If you want to how your body adapts to high altitude and will be in the Denver area, come visit Expedition Health at the Denver Museum of Nature & Science, which takes you on a virtual hike up Mount Evans, a Colorado fourteen thousand feet peak, and shows you how your body changes in ways you can see, measure and optimize.