Okay guys, in this lesson we’re going to talk about the movements associated with breathing. You’ll remember in the respiratory structure and function lesson we talked about the lungs being inside the thoracic cavity – what we’re going to see here is how that plays a role in our actual ability to breathe.

Some basic things you need to be aware of before you can understand breathing movements is the anatomy of the thoracic cavity as it relates to lungs. We talked about these membranes in the membranes lesson if you want a little refresher. Any time we’re talking about the lungs or the thoracic cavity, we’re going to use the word pleura or pleural. So let’s remind ourselves of this – we have the parietal pleura, which lines the thoracic cavity, then we have the visceral pleura around the lungs themselves. Then, in the space between those, we have pleural fluid – that pleural fluid contains surfactant and basically serves to stick the two pleural membranes together. SO – what we see is that if the thoracic cavity expands – it pulls the lungs out with it. If it contracts, the lungs will also contract down. So – let’s see what that looks like when we’re actually breathing.

Let’s talk about inhalation or inspiration first. Now no matter whether we are breathing normally at rest or heavily during exercise, inspiration always happens the same way. First thing we’re going to see is the external intercostal muscles and the diaphragm contract. When that happens the ribs will move up and forward – go ahead and breathe in – you’ll see your ribs move up and forward! Normally the diaphragm is in this dome shape, but when it contracts it flattens out and moves down. So with those two movements happening, the volume of the thoracic cavity expands – and like we just said – when the cavity expands, so do the lungs. Now, here’s the part you need to get. When the ribcage pulls the lungs open like this, it actually creates a sucking action by causing a negative pressure inside the alveoli. Try this – put your hand over your open mouth and try to breathe in through your mouth – you’ll feel that sucking pressure. So when we breathe in, we are actually PULLING air into our lungs because of that negative pressure going on.

Now, let’s look at the opposite process. Exhalation can happen differently depending on whether we are at rest or in exercise. At rest, it’s more of a passive process. Basically we just reverse the actions we just saw with inhalation. We relax the external intercostals and relax the diaphragm. that allows the ribs to move back and down to where they were and the diaphragm comes back up to that dome shape. So – the overall volume of the cavity decreases. Now, think about if you had an inflated balloon and you let it go – the elasticity starts to make the balloon smaller… so, what happens to the pressure inside? It goes up, right? And what happens to the air? It gets pushed out of the hole. Same thing happens here – we let these muscles relax back down, so it creates positive pressure and pushes the air back out of the lungs. It’s a relatively passive process. Contract to inhale, but just relax to exhale.

Now – this process is a little different if we’re doing vigorous exercise. Instead of a passive process, it becomes an active, more forceful process. So we will still relax the external intercostals and diaphragm just like before, but we will ALSO contract the internal intercostals, which forces or pulls the ribs down and back faster than just relaxing the other muscles. We also contract our abdominal muscles, which increases the pressure in the abdominal cavity, which will force more pressure upward into the thoracic cavity. So instead of just relaxing, we’re actually FORCING this cavity to be much smaller, much faster. So rather than just passively pushing air out, we’re actually FORCEFULLY pushing the air out of the lungs. That allows us to breathe faster and deeper during exercise, but to still get the ventilation and respiration we need.

Now, quickly I just want to cover some terminology when it comes to breathing. It all has to do with how quickly and deeply we are breathing. For all of these you’re going to see the suffix p-n-e-a. That suffix refers to breathing. It’s different than -penia which would mean too little cells, like in thrombocytopenia. The first one is eupnea – think of the word “euphoria” – this is like wonderful, perfect breathing. So eupnea is normal rate, normal depth – normal breathing. Tachy means fast and brady means slow. So Tachypnea is fast breathing and bradypnea is slow breathing. Apnea – remember an ‘a’ in front of something means absent or none – so Apnea is a LACK of breathing – this is literally when someone is NOT breathing. We may also say they’re apneic. Hyperpnea – you know hyper means high or a lot, right? So hyperpnea is fast, heavy, deep breathing. This is more than just tachypnea – they are also taking super deep breaths, not just breathing fast. And last is dyspnea – think “dysfunction” – this is irregular or labored breathing – usually found with some sort of disease process.

The other thing you need to understand with this breathing process is the various lung volumes. I’m going to draw a quick little diagram here for you to understand this better. The first term is Tidal Volume – sometimes written TV, sometimes written VT . This is the total volume of a normal breath – when I breathe in and out fully, how much volume did I move with each breath. Then we have what are called residual volumes, both inspiratory and expiratory – that’s the extra volume we COULD pull even after a normal breath. Try this – take a normal breath in and hold it. Then without exhaling, breathe even deeper – that’s your inspiratory reserve. Then take a normal breath and breathe out normally, then try to blow more air out – that’s your expiratory reserve. All of that volume together – the tidal volume plus reserves is our vital capacity. We also have a little bit of air left in our lungs after that, which is called residual volume – and when you add that to everything else, you get total lung capacity. The only other thing to be aware of is what’s called Dead space Air – that’s the air in our upper respiratory tract that just always stays there because it’s always open.

So let’s recap the key points here. Remember that pnea and pleura refer to the lungs and breathing – medical terminology is super helpful for these things, so make sure you review that. Remember that when the thoracic cavity expands, the lungs also expand, and vice versa. So what we see is that those movements of the thoracic cavity will change the pressure inside the lungs which is what either pulls air in or pushes it out. And remember that exhalation during vigorous exercise is a more forceful exhale by contracting those internal intercostals and abdominal muscles to really force the air out harder and faster. And make sure you review the volumes – the big ones you need to know are tidal volume and residual volumes, which together make up our vital capacity.

As you are breathing in and out today – pay attention to which muscles you’re using! That will help this to all click for you! And, as you start learning about disease process, think about how anything that impacts these muscles could impact our ability to breathe. Now, go out and be your best selves today. And, as always, happy nursing!