Pulmonary Ventilation and Altitude
This is a post about your lungs. I’m going to allow you a minute to get in the right mindset because they’re probably not something you think too much about.
Good? Good. Specifically, I’m going to talk about why it feels like an elephant is standing on your chest when you’re trying to be athletic at altitude when you spend most of the year at (or near) something approximating sea level. First, a bit of anatomy.
So what you’re looking at is the pulmonary anatomy, where gas exchange occurs in the lungs. There is an interface of capillaries and alveolus that allows for red blood cells to collect oxygen from the air drawn into the lungs. While the lungs are very elastic, they don’t control the pressure that allows filling to occur. For that, you have a swath of muscle tissue, shown here:
On the left you see muscles that are used to create negative thoracic pressure. Specifically, the diaphragm pulls down while the intercostals flare the ribs out, reducing compression on the thoracic cavity, thereby allowing air to be driven in my atmospheric pressure. So you’re not “sucking” air as much as you’re “creating space for the environment to move air into your lungs.” This tends to blow peoples minds. But once the air is there, how does this happen? As mentioned above, at the capillary-alveolus interface. Take a look:
So you have these super tiny spaces, the alveolus, where oxygen gets into the nooks and crannies. Individual red blood cells get into the capillaries that interface with these spaces, where the red blood cells offload CO2 and pick up O2. Awesome.
So where does this all go wrong at altitude? Well it’s really about what we call the partial pressure. At sea level there is a uniform atmospheric pressure that is acting on the gases in the air, which are nitrogen, oxygen, and carbon dioxide. These gases each have their own partial pressure, which is the pressure of that gas if it alone occupied the volume of the mixture at the same temperature (and altitude). Add those up and you get the atmospheric pressure at sea level, like this:
So what happens at altitude is that, while there is exactly the same percentage of oxygen in the air, the atmospheric pressure drops very fast. As a result, the saturation of hemoglobin (the oxygen binding pigment in red blood cells) cannot “grab” as much oxygen per unit of time. So it feels like an elephant is on your chest because you’re experiencing oxygen deprivation.
However, it’s important to note that this effect doesn’t happen until ~4900 feet above sea level. Once you’re above that, your body deals with it in interesting ways, like breathing faster, increasing heart rate, and adjusting its blood chemistry (mostly by increasing red blood cell count). The last part is why blood doping and the use of drugs like EPO are illegal in sport: they increase the red blood cell count, which increases blood oxygen, improving performance. It takes roughly 11 days per kilometer of altitude to manifest these changes.
Finally, the best way to “leverage” this, if you happen to be an endurance athlete, is not to train at altitude but to live at altitude and train below 4900 feet. This way you gain the advantages of altitude without compromising the intensity required in your training. It should come as no surprise that there is an Olympic training facility in Salt Lake City (Elevation: 4,226 ft) but athletes live in Park City (Elevation 7,000 ft).
If you’ve ever wondered why this happens, I hope this answered it for you!
Skyler Tanner is an Efficient Exercise Master Trainer and holds his MS in Exercise Science. He enjoys teaching others about the power of proper exercise and how it positively affects functional mobility and the biomarkers of aging.