Hello, this is our second video that is going to focus a little bit more on lung volumes. I'm looking more closely at the air that we're bringing into our lungs. And then, we're also going to talk about lung compliance, which is the idea of how distensible the lung is and what that means for lung function. So, let's start off talking about lung volumes where we've already talked about tidal volume. We said, that is how much air we're breathing in or out during a normal breath at rest. We also said that was about a half a liter. Here is a graph of different Lung Volumes Here at the beginning, the subject or patient is breathing normally with just normal Tidal Volume up and down, air in and out. Then at this point they're told to breathe in absolutely as much air as they can. If you take a normal breath, then you can fill your lungs even more. That extra air that you can add to your lungs above your normal tidal volume is called the Inspiratory Reserve Volume. That's what's shown right here.It is this portion of the curve. Most of these values can be measured with just a hand held spirometer. It's very easy to measure these values. These values are going to be important for diseases. These values are can change with disease. We'll be talking about that a fair amount. So you've got the amount you can inhale after you've already taking a normal breath that inspiratory reserve volume. It helps to kind of try this out I think to get a sense of what I'm talking about. Then you can do a normal exhalation and then exhale even more. So in a similar way this is going to be Expiratory Reserve Volume. Now you've completely removed as much air from your lung that you can remove, If you exhale completely you still have air in your lung. Otherwise your lung would completely collapse, which is very difficult to overcome because of the surface tension of water. So, that air that's left in the lung, is perfectly normal and very important. It is called the Residual Volume. We can put these numbers together to come up with some capacities that are important for understanding the lungs. If you exhale, a normal exhale, and then completely fill up your lungs, this adds to a total volume that includes the Inspiratory Reserve Volume, tidal volume and inspiratory reserve volume, This is the inspiratory capacity. This that really important number called the vital capacity. That is if you take a complete breath in so that your lungs are completely full and then you exhale all of that air as mush as you can, that determines the vital capacity. So that is the capacity that you can use. It doesn't include residual volume. But you can't use residual volume to bring air in or out of the lungs. So vital capacity is important. You can also determine total lung capacity which would be vital capacity plus residual volume. As you can imagine residual volume is going to be difficult to measure. It's possible to measure it but you can't measure with just a small hand held spirometer because the spirometer is measuring the air coming in and out of your lungs. And residual volume does not come out of your lungs. We can also look at functional residual capacity which is basically the volume of the lung once you've exhaled a normal breath. The next line slide will give you the definitions of all these terms, but before we move on, I just wanted to point out that these values as we've mentioned already are going to change with certain disease states. One thing that you can look at is the residual volume comparing it to total lung capacity. So what proportion of all the air that's in your lung can you not expel? The residual volume. There are going to be certain diseases called obstructive diseases where it's hard to exhale. So as you can imagine in these diseases, patients will tend to have an increase in residual volume. Since they have problems in exhaling, they end up having more air within their lungs once they'd exhaled versus in a restrictive disease condition. We'll be talking about examples of this in a minute. There can also be a problem in which you can't open up your lungs like a person with normal lungs. In that case, total lung capacity will decrease. Here's that slide I was mentioning where I have listed these terms and their definitions which I've just gone over. Now we're going to switch to talking about this two lung diseases, types of lung diseases. Obstructive diseases versus restrictive diseases. We will be referring to these throughout the rest of the videos so it's important to get an understanding of these states because they're really are helpful in understanding how the normal lung functions by comparing what happens in these diseases. As I've mentioned, an obstructive disease means that it's hard to expire. That often means that the residual volume can increase. Examples of this would be in asthma when you're going to have inflammation and contraction of smooth muscle in the airways so that you're going to increase resistance. Another example is COPD, chronic obstructive pulmonary disease, which comes kind of in two flavors. Chronic bronchitis, which is where you have a lot of mucus in the airways. People can have also emphysema or they can have both forms of COPD where the alveoli are destroyed. The problem is due to a lack of elastic tissue. Which means that the lung is very easy to open and fill but then it doesn't have that recoil to exhale. In some of these diseases you can also get collapse of small airways. We're going to be talking more about this but it kind of is anti-intuitive that you'd have a disease where it's only hard to exhale. You would think the same processes would also effect inhalation. The important thing to keep in mind is that when you're inhaling, you're opening everything up. You're stretching those airways even if they're collapsed. So in that way, you can have this processes that doesn't really affect inhalation very much. What is affected is exhalation. Particularly exhalation, when you're really having to squeeze out the air to get it out quickly. Because that's a compressing process. If you already have a problem with small diameter or with something that collapses easily, then exhaling is going to be much worse and be much more difficult. The restrictive lung diseases are those in which the lungs cannot expand for some reason. So total lung capacity is then decreased. One example of this that we will be considering are fibrotic diseases in which connective tissue is added to the walls of the lung. Connected tissue doesn't stretch. So the stretch, elasticity of the lung has been removed. You just can't stretch it as much and total lung capacity decreases. There can also conditions such as scoliosis, when you have a curvature of the spine that literally prevents the chest wall from expanding. It's going to have the same effect of preventing a large increase in volume and reducing total lung capacity. So we're going to use these diseases to look at what happens when we consider compliance of the lung. Which is going to be defined by the change of lung volume that occurs when you change the transpulmonary pressure. When you change the pressure across the lung. You could think of it as if you apply a certain amount of force basically to open the lung. How much does it open? how much does the volume increase? That's what's shown here. We' have pressure on the x-axis and lung volume on the y-axis. Let's consider a normal lung which is the blue line. If you apply a certain pressure, the lung opens and that continues at a pretty linear fashion until you get up here where we're starting to get a plateau. This makes sense because here you got a very high lung volume. Your lungs are all ready full.. You can apply a lot of pressure but it's not going to get bigger because it's full. This is perfectly normal and it makes sense. This is kind of at a normal amount of compliance which you can also think as distensibility. How easily is it opened? Now, the thing to keep in mind with the lung is as compliance increases, recoil is going to be inversely proportional. So if compliance increases recoil, which is the amount that it's going to shrink is going to be changed in the opposite direction. That's what we're going to talk about now. In a normal lung you've got kind of an immediate medium amount of compliance and a medium amount of recoil. In a disease where you have increased compliance which is this green curve, it is easy to open the lung. You can see we're applying a small amount of pressure and we're getting these huge lung volumes. They have increased compliance. But, if you have increased compliance that means recoil has gone down. You can think of this as in emphasema when the elastic tissue has been destroyed. That means you've got nothing to oppose opening the lung. That means it's easy to fill it. But then the problem is you need that elastic tissue, you need that recoil to cause the air to come out. So you've made it easier to breathe in but harder to exhale because you've increased the compliance and decreased the recoil. So you could think of this in a very extreme way. Consider this paper bag. Where I've got very high compliance. It's going to be easy for me to put air in here and expand that bag. But then I'm going to have low recoil. It's going to be hard for the air to come out. Okay, so here I filled the bag very easily but then the air isn't really coming out of it because it's got basically no recoil. So this is increased compliance and low recoil. Let's talk about the other situation where we would have decreased compliance. Which means, we're applying lots of pressure or force and our lung volumes are not increasing very much. So we've got, let's say an increase in connective tissue. , This means that the lungs just aren't going to stretch the way that they should. It will take more force, energy, pressure to get air into the lung. So we decrease compliance but that means that we've increased recoil. It's going to be easy to get the air out. An extreme example of that would be this balloon. It's going to take me a lot of pressure and force to fill this balloon, especially compared to the paper bag. But then when I let go, air's going to come rushing out because it's got lots of recoil. [SOUND] Okay? So there is low compliance and a high recoil in the balloon. So obviously our lungs are going to fall somewhere in between these two examples. But that you need both. You need to be somewhat compliant and need to have a certain amount of recoil for the lungs to function properly. So what is so important? What are the properties of lung that allow us to have this compliance? We've already talked a little bit about elastic tissue, which will make it harder to fill it, but definitely will provide that recoil of the lung. In emphysema We're destroying that elastic tissue and so compliance increases. In fibrosis, we're adding connective tissue that doesn't stretch to the lung. And so, the lungs are not as distensible. Compliance is going to decrease. The other factor in compliance of the lung is surfactant. Remember, Type II cells of the alveoli make surfactant. They actually make it in response to the lung being stretched. Surfactant is a detergent like molecule. That's what shown down here. It has a hydrophilic and hydrophobic portions in the molecule. That is what helps it reduce the surface tension of water. Every time we breathe we expand the lung. We have to fight or to combat the surface tension of water. We have to overcome that force. Surfactant reduces the surface tension so that it doesn't require as much force to open the lung. This is most easily demonstrated in certain premature babies, who, because they're premature, are not yet making surfactant. To breathe, just normal breathing, requires a tremendous amount of energy for these babies. They can die from exhaustion trying to breath. It's a very illustrative example of how much force it takes if you don't have surfactant in your lungs. Luckily, babies can be treated with surfactant that can make their breathing normal until they start making surfactant themselves. Another side note is just that there are other surfactant molecule types that are important in lung defense. Another issue in the surface tension situation is that our alveoli in our lungs aren't going to be exactly the same size. Because of that then you have to worry about what's happening with the pressure and if it's going to be equal. Law of Laplace says that the pressure in the alveoli is going to be equal to two times the surface tension divided by the radius. Since a radius is involved in the pressure in the alveolus, and we can have alveoli that are different sizes, that means that if we have the same surface tension in two differently sized alveoli, we're going to have a difference in pressure. Which means that the smaller alveoli that have the smaller radius, would have a higher pressure. Consequently air will flow from the small alveoli to the large alveoli, which is not the direction we want the air to flow. The amazing thing about surfactant is that it preferentially lowers the surface tension in the smaller alveoli. So that now the small alveoli and the large alveoli have the same pressure. That's what's shown here. It lowers the surface tension in the smaller alveoli more, so that even though they have a different radius, the pressure in alveoli number one and two are the same. So that's another important aspect of surfactant, just based on its molecular properties that it's able to do that. We've talked about different lung volumes, how we can measure them, and how they can change a little bit in disease. We'll be talking about that more in the future. Then we also talked about compliance, so that is a measure of distensibility. If it increases then that means the recoil wlll decrease. They are inversely proportional to one another. And we talked about how in restrictive lung disease, the lung is going to have low compliance but have high recoil. In an obstructive lung disease, we will have high compliance but low recoil. We'll be talking more about these two types of diseases in future sessions.
