Causes and Effects of Hypoxia on Pilots
Causes and Effects of Hypoxia – Video Transcript
Today, we are going to talk a little bit about an aeromedical factor and that is hypoxia. The first thing that I want to do is talk a little bit about these symptoms like, what are the effects of hypoxia? Over here I have some of those effects and I want to walk through each of those, talk a little bit about them make sure we know what they are, and then what I want to do is dive into different types, or a better way to say that is maybe different causes, of hypoxia.
As far as the effects are concerned, first one listed here is headache. I think everybody is familiar with what that is. Another common one would be impaired judgment or increased response time. So, you’re slower and you’re not really able to do things as quickly as you could, or you’re not really good at making good choices with the available information. Cyanosis is another common symptom. It’s when your lips or your fingernails get blue. Drowsiness and potentially something like numbness [are additional symptoms]. These are all effects of hypoxia and what’s interesting is different people tend to experience hypoxia differently, so really the only way that you would know is to have experienced it yourself as to which of these effects you’d be more prone to. A common example of what a lot of pilots would do in that case is visit something like an altitude chamber where they can depressurize this room and ultimately you can sort of experience the effects of hypoxia. Now what I want to do is talk a little bit about different causes of hypoxia. In some cases, they refer to them as the types of hypoxia, but the reality is it’s easier remember how these four things are really just different causes for this hypoxia. We’ll dive into the first one with hypoxic hypoxia.
As we get started with hypoxic hypoxia, I first want to talk a little bit about hypoxia and what we’re meaning. This implies that our body is unable, or in some way, unable to get the oxygen that it needs so our cells are in some way unable to get the oxygen that they need in order to continue to function normally, and so each of these different types of hypoxia that we’re going to talk about are really just different causes. In the case of hypoxic hypoxia, what this implies is that there’s an insufficient amount of oxygen available for us to breathe. Let’s put that to an example.
The most common example that I think we can discuss would be something like altitude, which is really about air density. As we climb in altitude, the air becomes less dense, which means the same number of air molecules take up a larger volume of air. Another way to think about that is our lungs, which have a fixed volume or a fixed size, can only take in so much volume. If the air is less dense, that means in that volume there are less air molecules, or specifically oxygen molecules available for our body to use. Examples of this that we might see in regular lives would be people that climb very large mountains such as Mount Everest have to bring supplemental oxygen with them on these journeys. This would be true as well then in aircraft. If we fly to high enough altitudes, either we would need to utilize some kind of supplemental oxygen, or we would need to pressurize the aircraft so that the air inside the cabin is representative of the lower or more dense air.
Another interesting example is more rare for sure, but it’s a good example to think of, is something like if we were transporting dry ice. Let’s say we were transporting something that needed to be cold and we were transporting it in dry ice. If that container that the dry ice is in is not well sealed, as that dry ice sublimates into a gas of co2, that would be a larger molecule and therefore displace the oxygen and the result of that could be that there’d just be an insufficient amount of oxygen available in the air. Once again, very rare examples, but something interesting I guess to think about. Next, we’ll talk about the second cause on our list which is hypemic hypoxia.
Next, we’re over here to hypemic hypoxia and what does that mean? Well, in this case we’re talking about the inability of oxygen to be transported by the blood. So hypemic hypoxia is we have enough oxygen coming into our lungs but at some point, the blood can’t carry it to all of our extremities to be used by the rest of our body’s cells. So, let’s think of some examples. I think probably the most common that we tend to discuss is carbon monoxide poisoning. In the case of carbon monoxide poisoning, this could be in something like a car or general aviation airplanes that are piston driven. Exhaust, for example, finding a way to get into the aircraft or into the vehicle. In that case, there is carbon monoxide in this exhaust gas and therefore we could potentially see the results of this. Why that’s relevant, and a little bit different from something like carbon dioxide, is with carbon monoxide poisoning what happens is this carbon monoxide ultimately attaches to a part of your blood that’s supposed to be carrying the oxygen. They call it a hemoglobin and it just stays attached because no cells of your body need to ever use it so it never gets taken out of your blood, or it doesn’t get taken out very easily, and so it kind of just stays attached. Which means your blood isn’t really able to be as efficient as it should be and therefore less and less oxygen can be transported. This is also true actually with smoking like with cigarettes. So, another common example would be something like that.
Another kind of example would be insufficient blood. So obviously if you were cut severely and you were bleeding significantly, an insufficient amount of blood means that there might not be enough blood to carry oxygen to all the parts of your body, but maybe a slightly less thought of example there, is if you donate blood. So, we go in to donate blood, you donate a significant volume of your blood, it doesn’t just replenish immediately. It takes a lot of time for your body to ultimately replenish all of the blood that you’ve donated. In that time, you may be more susceptible to something like this hypemic hypoxia, something to consider.
Other examples could be different blood diseases like anemia or something like this, but as far as it relates to maybe us as aviators, I think something like carbon monoxide poisoning is something to keep in mind as well as once again actions that we take when we’re not flying for example donating blood or something to this effect. Now we’ll jump over and talk a little bit about the third type of hypoxia, stagnant hypoxia.
Now with stagnant hypoxia, we have oxygen in the blood, it’s good to go, but it can’t make it to the cells that need it. So, in the case of stagnant hypoxia, we think of the word stagnant, meaning like stable or not moving so that would be a common example. So in this case, thinking of some of those examples, we can have some kind of restriction in our veins or our arteries and so this could be as simple as you sit down for too long, you sort of cut off blood flow, and you stand up and you say, “oh my foot fell asleep”, that’s an example. Or, obviously physiological issues with your blood vessels themselves, this could also be something like a heart condition possibly, where your heart is unable to pump adequate volumes of blood.
More common I think in the flying side of things is something like load factor. So if we were to do a high-g maneuver, blood will be forced to move down towards the bottom, or in our case if we’re sitting down it would move out of our heads and down through our bodies as low as it can go, so this obviously would be an example of something causing the blood to not be able to flow to all the cells that need it. I think these two are pretty good examples of something like stagnant hypoxia, but probably a little less likely if you’re not doing a lot of load factor during your particular flights. Now we move on, we’ll talk about our last form of hypoxia here, last type called histotoxic hypoxia.
As you may have guessed from the word toxic, meaning like poisonous, histotoxic hypoxia is a scenario where in which basically your cells are poisoned. What that means is, we have oxygen-rich blood and that makes it to the cell and says here’s your oxygen, and the cells say no can’t take that, and then they’re unable to actually get the oxygen out of the blood. Usually it has something to do with cellular transference but the whole point is basically the cells, you can think of it, are saying now I don’t need any of that oxygen. So most common causes are alcohol, as a great example. I think that in the case of alcohol, anytime you’re consuming alcohol this is the result of a lot of the feelings that you get when consuming alcohol are hypoxic feelings in a lot of cases, and that is just a result of this histotoxic hypoxia. There are other drugs or poisons that would basically serve the same function and it basically prohibits that cell from collecting oxygen from the blood. This is why we have such tight restrictions in a lot of cases on the use of alcohol for example. In aviation it can have dramatic effects to our ability to operate safely.
So, a real quick recap of what we’ve talked about so far when talking about ways that we can deprive our body’s cells of oxygen, which is hypoxia. There’s sort of four different ways to do that, or four different types of hypoxia, and so real quick as a sort of review hypoxic hypoxia meant that we didn’t get enough oxygen into our bodies so we were unable to breathe enough oxygen or there just wasn’t enough oxygen available. Hypemic hypoxia meant that we had enough oxygen coming in, but it wasn’t able to get to the bloodstream. Stagnant hypoxia means the blood could collect the oxygen but then couldn’t transport it to the cells that need it, and last the histotoxic hypoxia is when the oxygen-rich blood makes it to the cells but the cells are unable to collect it. So, in each of these cases obviously we should be vigilant and ensure that we don’t become susceptible. I would invite anyone who is a pilot to probably figure out where the nearest altitude chamber is and go have a try with experiencing hypoxia for yourself. I think it would help you understand the symptoms you would feel and maybe would help you later on understand if you ever started to feel those effects in flight.