[BLANK_AUDIO] Now, why do we care about changing the volume of the lung? We inhale and that increases the volume. What does that do? Lauren. >> Increases lung volume. >> Well, the lung volume increases, and what results when we increase the lung volume? What does that cause? >> [COUGH] decrease in lung pressure? >> Exactly! It causes a decrease in intrapulmonary pressure, the pressure inside the lungs, and when intrapulmonary pressure decreases, what's going to happen? >> Air flows into the lungs? >> Exactly! Exactly, so when we decrease pressure in the lungs, pressure in the lungs is less than atmospheric pressure, air will move into the lungs, okay? Then inhale is done [SOUND] we quietly start to exhale. Lung volume decreases, what happens? >> Intrapulmonary pressure increases? >> Exactly, and then what's that going to do? >> Air flows out. >> Exactly! Because intrapulmonary pressure is going to be higher, than atmospheric pressure, air will move out of the airways. Excellent, excellent. Now take a look at this picture that's open in front of you [SOUND] because I want you to notice, this is a tracing of volume changes in the lungs. We call this a spirometry tracing, and it's a tracing, you know, of what happens as you inhale and exhale. You can see that as you inhale, lung volume increases, right? And then you can see decreases in lung volume. Those would be associated with exhaling, right? So, when you're sitting around breathing normally and quietly, what's, what's that volume called, that volume of air that moves in and out of the lungs during quiet breathing? >> Tidal volume? >> Yes, exactly. And looking at the graph, the graph is representing to you, on average, what volume of air actually does move in and out of the lungs, and what is that volume? >> 500 millilitres? >> Yes, so about 500 millilitres of gas or air moves in, and then out of the lungs, with each quiet breath that you take. Now, when you are, you know breathing more forcefully, because you're, you know activating those accessory muscles, you take, you, you know, you, your lung volume is going to increase more than it does when you are breathing with a tidal volume. So the lung volume increases more, that means intrapulmonary pressure will be a little bit lower, right? More gas will move into the lungs. If we would increase the volume of air that's moving in or out of the lungs, we would be using part of a lung capacity, that you call what do you think? >> The inspiratory reserve volume? >> Yes, we would be moving into our inspiratory reserve volume. Now you can see from looking at this graph, that there is a maximum inspiratory reserve volume, right? There's a maximum amount that you can inhale, when you're breathing in as forcefully as you possibly can, right? Same thing with the expiratory reserve volume, there seems to some lower limit to how much we can maximally exhale if we need to, right? And so one of the capacities that's very important when we think about lung function, we think about your vital capacity, right? Now, if you look at the graph, you see that vital capacity, represents that volume that we can measure when the lungs are maximally filled during an inhale. That would be the highest volume, and then it tells us something about the lowest volume that the lungs could be holding at the end of a maximal exhale. So if you were measuring that vital capacity, you would ask your patient to inhale as deeply as possible, then exhale as forcefully as possible, and you would see would their vital capacity is. At the end of that maximal exhale, when you have emptied as much air out of the lungs as you possibly can, is there any air left in the lungs? >> Yes. >> Yes, Lauren. [CROSSTALK] What are you seeing when you look at this graph? >> That is the residual volume. >> That we have residual volume left in the lungs, yes. Now, what's the benefit of having some residual volume? >> Jane? >> The, it keeps the alveoli open. >> Yes. >> And prevents [CROSSTALK]. >> It does help to keep the alveoli open. So if those alveoli totally collapsed, it would be very difficult to take your next breath, right? And by keeping the alveoi open, we make it easier to take the next breath. Now, that collapsing of the alveoli, making it difficult to inhale the next breath, represents a change in resistance, in the respiratory system, right? So, when we are thinking about the volume change causing a pressure change, which causes gas to flow in and out of the lungs. We also have to consider that if for some reason the resistance in the airways changes, it makes it more difficult to breathe. Can you think of any time that the resistance might be changed in the airways? Lindsey. >> Well, I have asthma, and I know that when my allergies are really bad, or if I'm having an asthma attack, it gets really hard for me to breathe. >> Exactly, yes. People that have asthma, or some kind of condition that causes a narrowing of the airways. Those people would experience a more labored or more difficult breathing, right? so, why could the airways become constricted? What allows them to constrict? Or what makes them constrict? If you want to think of it that way. Jane. >> The sympathetic nervous system. >> Well we, we won't even get into the nervous system yet, and I want you to think about smooth muscle. We have smooth muscle in the walls of the airways like the bronchi and the bronchioles. And if that, that smooth muscle encircles the airways like this, and so if we contract that smooth muscle, we narrow the opening through those airways, we call that bronchioconstriction. And when bronchioconstriction occurs and the airways are narrower, it's more difficult to move air through the airways, right? The contrast would be, when you go out for your daily cardiovascular exercise, what happens to the airways? They bronchiodilate a little bit. Yes, because that then allows to move in and out of the lungs more easily. So it's actually the sympathetic nervous system, that's going to cause that bronchodilation, right? And the parasympathetic nervous system, that will cause bronchioconstriction. People that have asthma, when you're in the middle of one your acute attacks, you'll take some kind of remedy, yes? A, a drug has been prescribed for you, probably, that acts like a sympathetic nervous system response would, it acts to the to bronchiodilate so that you can breathe more easily, okay? so, what is that normal volume of air that moves in and out of the lungs when you're just sitting around quietly? Lindsey. >> Tidal volume. >> Yes. And, if you have to breathe more forcefully, and you inhale more deeply, you are inhaling. >> Your inspiratory reserve volume. >> You're moving into inspiratory reserve volume, yes. And if you exhale more deeply. You're exhaling part of your. >> Expiratory, expiratory reserve volume? >> Exactly, your expiratory reserve volume. And Jane, if I inhale as deeply as I can, and then exhale everything I possibly can, what is that volume of air called? >> Your vital capacity? >> Exactly! And are my lungs totally emptied of gas? At that point, no. What's left? >> The residual volume. >> The residual volume is still there. Great job, you guys. [BLANK_AUDIO]
