Welcome back, this is our last video about the respiratory system, we're just going to consider some disturbances in oxygen and proton balance. We're going to consider what happens when we exercise and then we will consider hypoxia, when the amount of oxygen is low in the blood. So we have, first what happens during exercise. This series of graphs shows what is going on when we're at rest versus vigorous exercise. As we move from being more and more active after we've been resting. So let's say that we start doing low intensity exercise, and then we do moderate exercise. The minute ventilation is going to increase. Okay linearly and that makes sense. As a result in that linear, linear increase in minute ventilation then the oxygen is, amount of oxygen is going to stay stable in the blood and the amount of CO2 will basically stay stable as well as the proton concentration. So we're matching our needs by increasing ventilation. Then, as we're getting close to maximal exercise, which is more vigorous, that's when we start to see a change. Where now all of a sudden. minute ventilation is increasing in a non- linear fashion. It is doing that because we see the arterial pH or arterial proton concentration is also increasing. in a non-linear fashion. This increase in minute ventilation is in response to an increase in protons because we're forming lactic acid. Basically, we're getting into a state of metabolic acidosis. Where we have an increase in protons, which is going to cause an increase in ventilation. So now we're basically hyperventilating. And now our PCO2 is decreasing. Okay? So that's something that is going to happen during exercise, in particular during vigorous exercise. The other thing to think about is the change in minute ventilation, as we're doing exercise, particularly, at the very beginning and at the very end. If you're a trained individual, your body learns to anticipate exercise. So, what we can get is this feed forward process in which the body knows that you're about to exercise. So that as soon as you start, ventilation increases more than it actually needs to. We saw in the last slide that it just kind of increased linearly as you. Increased your intensity. Here we're having this large jump at step one where we have this instantaneous increase in minute ventilation and anticipation to kind of get a jump start on ventilation. Then as we keep going, it's going to. gradually keep increasing until we get to the end. Here we will have a pretty rapid drop in ventilation, but it's not back down to baseline. It's well above baseline, and then it slowly decreases down to baseline. So you're continuing to breathe more heavily than you need to considering what you are now doing. You all know this. If you sprint for a long distance and then stop you are now at that point of maybe just walking or standing but you are still breathing very rapidly. That's occurring so that you can get all your systems back to base line. You're trying to remove what's called the oxygen debt. Because of your exercise you have depleted the stores of oxygen-saturated myoglobin. This is a molecule that's very similar to hemoglobin. It is in the muscle. It can store oxygen in the muscle. After you exercise, those stores are depleted. You're trying to keep that extra oxygen coming in to load up myoglobin again. Then remember, in muscle, we also talked about creatine phosphate. This needs to be converted back so that it can be used again. Those processes are going on over the next several minutes. They are regenerated through this increase in oxygen uptake. Then, we also might have lactic acid around. So that might also be an aspect of the increased ventilation which corrects an acid-base imbalance as well. Okay, so we've talked about exercise. Now we're going to finish up talking about hypoxia, which is a deficiency of oxygen in the tissues for some reason. There can be different types of hypoxia. We can talk about hypoxic hypoxia, which is a little redundant. What the problem is is that we have low oxygen in the blood. That's the issue. That is separate from having hypoxia because we're anemic. Here we, for instance, don't have enough red blood cells. The PaO2, the PaO2, the arterial pressure of oxygen, is just fine, but we have low oxygen content. Because, remember, hemoglobin's going to represent 98% to 99% of the oxygen in the blood. We can also have an issue where the amount of oxygen in the blood is just fine, but we have low oxygen delivery. So for instance, if we had a blood clot the prevented blood flow. That would be ischemic hypoxia. Or, if you put a tourniquet on your arm, then your arm is going to have ischemic hypoxia because you don't have blood flow. But the amount of oxygen in the blood is just fine. Then there's histotoxic hypoxia, which is when there is oxygen in the blood. and there is delivery to the tissue, but if you have something like cyanide present that prevents the use of the oxygen. That would be histotoxic hypoxia. It's basically like there isn't oxygen there because you are not able to use it. In the case of cyanide, the tissue is hypoxic because electron transfer chains in mitochondria are disrupted by cyanide. Let's talk a little bit more about some causes of hypoxic hypoxia. What are the things that can prevent you from having enough oxygen in the blood or more specifically, a low arterial pressure of oxygen? One is going to be hypoventilation. If for some reason you are not breathing enough. The other could be diffusion impairment, which we've talked about a little bit. Here you might have normal alveolar pressure of oxygen but then if you have liquid, or mucus, or connective tissue that is preventing diffusion then that can easily affect the pressure of oxygen in the blood. Then we can have ventilation-perfusion inequality. We've talked about how we all, even in a normal lung, have some V-Q mismatch, but then how we can have some other pathological issues or other issues that can cause an increase in that ventilation-perfusion mismatch. Another thing that can cause hypoxic hypoxia is sleep apnea, which is a increasing problem where, when you sleep, you are going to have a reduced frequency of breathing. You're going to have a decreased flow rate when you breathe in, so you're going to be breathing less often. You're going to be taking in less oxygen as well, or less air. That means that your minute ventilation is going to basically decrease. In addition, skeletal muscle is going to relax. You're going to have reduced tone in your skeletal muscle. That can cause a collapse of the upper airways, like the pharynx and larynx, in the mouth and throat. Then also your tongue can cause an occlusion of the airways. It can cause you to make sounds such as snoring. But then, if you have a complete occlusion of the airway, we refer to it as sleep apnea. Here you can stop breathing for 30-60 seconds and then basically you will wake up very often and gasp for air. The kind of scary thing about this is that often when you have sleep apnea, it's not that you're doing this once a night, that you're stopping breathing for 30 to 60 seconds. It can be many, many times just in an hour. It's obviously not good to be oxygen deprived, but then, also, not good to be sleep-deprived. You're really basically waking up at least at some level. It might not be really at a conscious level, in order to open those airways back up. So, we have a question of what's going to stimulate you to wake up and to fix your breathing? We know that you are most sensitive to the arterial CO2 pressure and so that's what is going to activate those central chemo- receptors to cause you to make sure that you breath. Really the best treatment for this prblem is based on the architecture of the nose or the throat. You can have surgery to fix this problem but there is also a machine called a CPAP machine that provides continuous positive airway pressure. It's a mask that people wear. It provides a continuous flow of air that's just enough to keep those airways open at all times. So that people breathe all the time. They don't wake up because of a lack of breathing. So, we've talked about exercise. That's going to be a time when we all are going to have to increase our ventilation, and, when we really get into the intense exercise, that's when we can start to have metabolic acidosis. That will cause us to basically hyperventilate, which means PCO2 will fall, but then that will reduce the amount of protons. This is to try to compensate for the metabolic acidosis. Then we talked about sleep and how it's going to cause us to breathe less. Sleep cause the airway muscles to relax which can cause obstruction, either complete, causing sleep apnea, or partial, which can lead to noisy sleeping and snoring. [BLANK AUDIO]
