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Right now I’m flying at 30,000 feet on my way to Denver, Colorado for a meeting about Pulmonary Fibrosis. I’m a lung doctor, so I’m always thinking about how lungs are working (or not working), and right now I’m wondering if I’m harming myself by spending a few hours at altitude.
As you might know, the air is “thinner” at higher altitudes, which means there is simply less air to breathe. Now, I’m not breathing “30,000 feet” worth of thin air – which would be really bad. Instead, since the air in the cabin of this Boeing 757 is pressured a bit, I’m breathing about “8,000 feet” worth of thin air. For someone with normal healthy lungs breathing comfortably at sea level, about 99% of the hemoglobin in the blood leaving the heart might be carrying oxygen -- that’s a normal healthy percentage. But with the thin air up at 8,000 feet, only about 90% of the hemoglobin is carrying oxygen.
Should I be worried?
Maybe. I’ll explain why…
The lung is pretty amazing organ. I run the pulmonary course for the medical students at Columbia University, and each year I have the pleasure of teaching the students how the lung moves oxygen from the inside of each of the lung’s air sacs into the blood that is rushing through blood vessels in the lung. This might sound simple, but there’s a serious problem that the lung has to take care of if it’s going to maintain normal oxygen levels in the blood.
I guess an economist might call it a “supply and demand” problem. You have millions of tiny air sacs in your lung, and each one has to transfer oxygen into the bloodstream. Each of your air sacs are a different size – big ones get lots of oxygen each with breath, and little ones get a small amount of oxygen with each breath. In addition, each air sac has blood flowing right past it – this is the blood that picks up oxygen from the air sac to bring it to the rest of the body. Some air sacs receive lots of blood flow and some air sacs receive just a little bit.
Now here’s the problem –- the size of the air sac doesn’t match up with the amount of blood flowing past it. So, you have a bunch of big air sacs with a small amount of blood flowing by – causing a backup of oxygen in the air sac. Without enough blood flowing by, the oxygen has no where to go and it stays in the air sac – these air sacs only transfer a small amount of oxygen to the bloodstream.
You also have small air sacs with way too much blood flowing past them – here the bloodstream will drain all of the oxygen out of the air sac, leaving an air sac that contains very little oxygen. These air sacs also only transfer a small amount of oxygen to the bloodstream.
Both of these situations – too big and too small – make the lung inefficient at doing it’s most important job – transferring oxygen into your bloodstream. Fortunately, your lung has two solutions – one is kind of obvious and one is way cool.
The obvious solution is that there are, of course, many air sacs where the amount of oxygen coming into the air sac matches up pretty well with the amount of blood flowing past the air sac. In fact, we often try to measure how well the oxygen coming in matches up with the blood flowing past the air sacs in people with lung disease – it’s a sign of how healthy (or sick) your lungs are. (It’s one of the reasons we do “arterial blood gases” or ABGs).
The way cool solution is that your lung can actually sense oxygen in the air sac – kind of a “sixth sense.” Remember the “too small” air sac? There was too much blood flowing past it and the blood ended up draining all of the oxygen from the air sac. Well, to prevent the oxygen level in the lung from going too low, the lung first senses the low oxygen levels inside the air sac and then actually redirects the bloodstream away from that air sac so that the blood can instead flow to bigger air sacs. That means that the oxygen level inside the small air sac will rise back toward the normal range (because the blood is no longer rushing past it so quickly and draining all the oxygen from it).
Now this part is really important (and it’s going to come up again in a minute): the way that the lung redirects blood away from the “too small” air sac is by simply making those blood vessel that deliver blood to the air sac shrink up a bit. When blood vessels shrink up, it is harder for blood to get through those tiny little blood vessels, and instead the blood will flow into other blood vessels that are not shrunken up – and which are therefore going to deliver blood to bigger (and perhaps healthier) air sacs with normal oxygen levels.
So, every day, everyone’s lungs are “working hard” trying to match up the amount of oxygen in each air sac with the amount of blood flowing past each air sac – and you have millions of air sacs. If the lung stopped trying to match up oxygen and blood flow, a “normal” oxygen level would be about 60% instead of 99%. It’s that important.
I’m up here at “8,000 feet” worth of thin air, but with pretty healthy lungs. So, now that you are “lung smart”, can you guess what my lungs are “sensing”? That’s right – they are sensing low oxygen levels inside of ALL of my air sacs. And that means that my lungs have told my blood vessels -- ALL of my blood vessels –- to shrink up in the hopes of sending blood to “healthier” air sacs.
But there are no “healthier” air sacs for the blood to go. Instead, my heart now has to pump harder just to push the blood through all of these really narrow blood vessels. I have a pretty healthy heart and the flight is only about 4 hours, so it’s no big deal for my heart to work harder and generate a higher pressure in order to push my blood through the narrowed blood vessels in my lungs.
Now imagine if it wasn’t 4 hours. Imagine my heart had to do all of that work all the time. My heart might not be so happy. It might eventually get weak.
Now stop imagining. Instead, think about what happens to you each day. Maybe you always have low oxygen levels, in which case you are putting strain on your heart 24 hours a day. Or maybe your oxygen levels only drop when you exert yourself – meaning that you are living in a cycle of heart strain dozens of times each day. Or maybe your oxygen levels drop at night. You would need a sleep test at home or in a sleep lab to figure that out.
Over time, those low oxygen levels eventually leave your blood vessels permanently diseased and narrowed. That condition is called “Pulmonary Hypertension”, which is a serious and life-threatening complication of Pulmonary Fibrosis. (Pulmonary Hypertension can also exist without Pulmonary Fibrosis).
Using oxygen to keep your oxygen levels over 90% 24 hours/day (90% 24/7) is one of the most important things you can do to keep yourself healthy if you have Pulmonary Fibrosis. Yes, it is inconvenient, frustrating, annoying, expensive (for some), and for many it is a difficult and embarrassing transition.
I want to acknowledge and address the embarrassment that many people with Pulmonary Fibrosis experience when first wearing oxygen in public or with friends and family. First, I do understand. I personally would have a very difficult time putting on a nasal cannula and walking around town or the hospital with an oxygen tank. The transition is hard. But remember these 4 things:
- Using oxygen is NOT a sign of sickness.
- With oxygen, you are healthier, not sicker.
- Using oxygen is NO DIFFERENT than wearing eyeglasses or using a cane.
- Some accomplishments are judged not by what you achieve, but by what you overcome.
Thanks for reading the whole post! In a future (and shorter!) post, I will describe what I believe to be smart and helpful ways to use oxygen in your everyday life.
Please share your thoughts about this post as well as your own experiences with oxygen use.