 Hey, how about we start this video by taking in a deep breath, okay? Let's start. Inhale, exhale. Felt good? Okay, you'll feel even better when I ask you a question related to it. What is the total volume of air that you inspired? Well, I'm sure you'll be able to answer this with few Google research, but then, why should we even bother to know about our lung volume? Well, if you have this exact same question in your mind, then let me tell you, lung volume and lung capacities are a big thing in medical science. Doctors can tell if you have a respiratory disorder or not by calculating your lung volume and capacities. And that is what we are going to look at in this video. But before we dig deep into this lung volume and capacities, let me bust a very common misconception about lungs. People often compare lungs with an inflated balloon. Just how a balloon is inflated when air goes in. Our lungs also gets inflated when we inhale, right? But when we deflate a balloon, all the air from the balloon goes out. It becomes completely empty. But that's never the case for our lungs. Even when we exhale out air, there is a good amount of air still left within our lungs. Interesting, right? So, to understand it even better, I have made a square here. And we will consider the total volume of air inside the square as the total volume of air that's within our lungs at any point of time. Let me repeat what I just said. The total volume of air inside the square is the total volume of air that's within our lungs at any point of time. Now let's say he is Ravi. And this is Ravi's lungs. Now Ravi is doing normal breathing. So when he inhaled, some amount of air got into his lungs. And when he exhaled, the same amount of air went out. Now this is how our lungs are made. Whatever amount of air you will take in, the same amount of air will go out. And this volume of air that comes in and goes out in each breath is called tidal, tidal volume. I'll just write V for volume, okay? And it is somewhere around 500 ml. I'll get rid of Ravi for now. And we will write 500 ml here, okay? And a normal person reads around 16 to 12 to 16 times per minute. So you can do the math, the total amount of air that gets into our lungs per minute is somewhere around 6000 ml to 8000 ml, which is around like 6 to 8 liters of air per minute. Okay, now suddenly Ravi decides to take a deep breath. So in deep breath, apart from the normal amount of air he was inhaling, he will take in excess extra amount of air now, right? So the extra amount of air that he takes in, apart from the normal amount of air which he would otherwise inspire, is called inspiratory reserve volume. And this is around 2500 to 3000 ml each time, which is huge, right? So this is the inspiratory reserve volume, this one here. This is the tidal volume. Now after this forceful inspiration, can you tell me what would be the total volume of air that will go out when Ravi exhales? Well, it will be inspiratory reserve volume plus tidal volume. Because as we have already discussed, the total amount of air that gets into the lungs, the same amount goes out during exhalation. Now let's say Ravi got back to his normal breathing rate. He is inhaling and exhaling just the tidal volume, okay? And again, all of a sudden he felt like forcefully exhaling. What will happen now? What do you think? Well, some amount of air from the volume of air that was already inside our lungs, some amount of air from here will be exhaled out. But remember, the entire lung will never be empty. So let's say this much was exhaled out when Ravi was forcefully exhaling. So what we will call this part, expiratory reserve volume. And this is almost equal to the amount of air that was left inside the lungs, which is around 1100 to 1200 ml. Now after forceful exhalation, when Ravi inhales, can you tell what would be the volume of air that would get in, tidal volume, plus expiratory reserve volume because it has to restore the volume of air that was already there in our lungs, right? Now the volume of air that is in this part of the lungs, you can never ever ever get this out of your lungs, okay? And we call this part or this volume of air as residual volume. This is again around 1100 to 1200 ml. So residual volume is the volume of air that can never be removed from the lungs. Expiratory reserve volume is the amount of air that is forcefully exhaled out. Tidal volume is the normal amount of air which comes in and goes out while we normally breathe. And inspiratory reserve volume is the excess amount, additional amount of air that we try to forcefully inhale, okay? Simple, right? Now when two or more of these pulmonary volumes are combined, it is termed as capacities. For example, if we consider the whole thing, the inspiratory reserve volume, oh, I should have told you about the short forms they have. They are also written as IRV, TV for tidal volume, expiratory reserve volume as ERV and RV for residual volume, okay? Now if we consider the whole thing, if we add up the whole thing, it will give us the total capacity of Ravi's lungs, right? Because Ravi's lungs won't be able to accommodate any more volume of air. This is the maximum the lungs can expand, right? So this total, the whole thing is called total lung capacity. Now can you tell me the maximum amount of air Ravi can inhale? It will be tidal volume plus inspiratory reserve volume, right? That is the maximum he can inhale. So both of these together is also known as inspiratory capacity. Same goes for exhalation. The maximum Ravi can exhale is tidal volume plus expiratory reserve volume, right? And both of these together are called expiratory capacity. Now if Ravi is inhaling and exhaling only the tidal volume, then the amount of air that will remain in the lungs undisturbed will be expiratory reserve volume and the residual volume, right? So this much amount of air always remains in the lungs until and unless a person goes for forceful inspiration or exhalation, right? So this two are together known as functional residual capacity. And this brings us to the end of the volumes and capacities of the lungs. And these volumes and capacity, they obviously differ depending upon the gender, age, ethnicity, body composition, etc.