Lesson video

Hi, there, and welcome to today's lesson.

I'm really looking forward to teaching you today.

My name's Mr. Schweiz, and this lesson is about the mechanics of breathing and interpretation of a spirometer trace.

Do you know what a spirometer trace is? Well, it comes from the unit anatomy and physiology, the cardiorespiratory system, and it's all about the lungs and how they operate, how volume and pressure changes drive air to rush in or out of the lungs.

So by the end of today's lesson, you're gonna be able to explain the mechanics of breathing and how lung volumes are measured.

So a number of key words we'll be exploring, and, in fact, there is more than this, but these are the ones that are probably newest to you.

So tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.

We'll also be talking a lot about inhalation and exhalation or inspiration and expiration.

You might wanna pause the video now and just make a note of these keywords, but we will be revisiting them during the lesson.

So broken up the lesson into three parts.

The first part, we're gonna look at inhalation.

(inhales) Breathing in.

The second part, we'll look at exhalation.

(exhales) Breathing out.

And then in the third part, we're gonna unpick those different lung volumes and how they respond to exercise.

So are you ready? Let's get going.

So here we are then, inhalation.

We've got an image here of the lungs and the purple arrows illustrating the movement that's gonna happen when we want to breathe in.

So inhalation, also known as inspiration, is that process of breathing in.

And we breathe in air by expanding our lungs.

So during inhalation, the diaphragm contracts down into a flattened shape.

So it's a dome shape when it's at rest, and it contracts down into a flat position.

At the same time, the intercostal muscles, which are in between each of your individual ribs, they contract and they pull the rib cage up and out.

So you've got the ribs moving up and out and the diaphragm moving down.

And it's a consequence of those two movements.

There's a bigger volume inside this chest or thoracic cavity.

And if the volume gets bigger, that causes a decrease in air pressure.

And if there's a decrease in air pressure, that's what forces air to get sucked into the lungs.

It's drawn in from the atmosphere due to those volume and pressure changes.

So let's do a quick check.

Inhalation and inspiration.

Do they mean the same thing? True or false.

That's right, it's true.

So inhalation and inspiration do mean the same thing, and those terms are often used interchangeably to refer to breathing in.

But remember, inspiration can also refer to creativity or motivation if it's used in a different context.

So sometimes I'm inspired by sports people that are amazing at what they do.

Okay, let's look at some of these air pathways then.

So we've got a cross-sectional illustration here, and we can see that air will rush in through the nose and mouth, and it's actually filtered through the nose, particularly well through your nose hair.

So it's best if you can to breathe in through your nose.

And it then travels down the trachea or the windpipe.

And that trachea branches off into two.

One branch goes into the left lung whilst the other branch goes into the right lung.

And when it branches, it then branches further into bronchioles.

So kind of a web, and I always think this looks a bit like broccoli and sounds a bit like broccoli, doesn't it? So you've got that main stem, and then it branches off into lots of little bronchioles.

And at the end of each of those bronchioles are the air sacks called alveoli.

So those are like the buds on the end of the broccoli.

They've got a massive surface area that enables gaseous exchange to happen.

So Sam's wondering, what does a flow diagram look like that would walk its way through the process of inhalation? Well, here we go.

First of all, the intercostal muscles contracts.

They're the ones in between each of your ribs.

If you ever like eating ribs, it's the intercostal muscle that you're eating, actually.

Fun fact, I have a theory that if you train your pigs at altitude, they will have to breathe harder to get air into the body, so they will grow more intercostal muscles, bigger and stronger intercostal muscles.

So I think they're gonna taste better if you eat ribs that have been bred at high altitude.

Don't know if it's true or not, but there we go.

So intercostal muscles contract.

And that causes your ribs to move up and out.

At the same time, the diaphragm is contracting down from a dome shape.

The sheet of muscle, that is your diaphragm, and that's the one you sometimes get a stitch in.

If, you know, sometimes you suffer from a stitch if you're exercising and particularly if you're exercising and trying to talk actually.

So the diaphragm moves down.

And those two things combined will increase the volume of the lung cavity.

And as a consequence of a bigger lung, sorry, a bigger volume, the pressure goes down.

And if the pressure is lower, then air will rush in.

Okay, let's do a quick check.

Which of the following is incorrect? So not true.

So the mechanics of breathing enable us to a, inspire air to get fresh oxygen into the lungs.

b, expire air to get rid of excess carbon dioxide.

c, decrease the volume of the chest cavity when inhaling, or d, increase the quantity of oxygen brought into the body during exercise? Which do you think is incorrect? Tough one that, isn't it? 'Cause there's lots of words, but it's c.

So c said there's a decrease in the volume of the chest cavity when inhaling, where actually the volume increases, which causes that decrease in pressure.

Okay, let's do a task to see if you can apply all of that learning that we've covered so far.

So there's a gap fill task where I've got a sentence written out, and I want you to fill the gaps using the words at the side.

So the what contract pulling the what up and out whilst the what also contracts and flattens.

This will increase the what of the what to reduce the air pressure, which initiates what, also known as what.

Something in via the nose and mouth and travels down the something, entering the left or right lung through the something.

These further subdivide into bronchioles before the air reaches the blank.

Blank happens at the blank where blank diffuses into the blood and blank diffuses out ready to be breathed out.

So you're gonna need to pause the video now whilst you fill those gaps and tick them off from the selection of words on the right-hand side there, and come back to me when you are ready.

Okay, how did you do? 'Cause I'd hidden an awful lot of words there, hadn't I? So you should have come up with the intercostal muscles contract, pulling the ribs up and out whilst the diaphragm also contracts and flattens.

This increases the volume of the chest cavity to reduce the air pressure which initiates inhalation, also known as inspiration.

You might have put those the other way round.

Air rushes in via the nose and mouth and travels down the trachea entering the left and right lungs through the bronchi.

These further subdivide into bronchioles before the air reaches the alveoli.

And then it's gaseous exchange happens at the alveoli where oxygen diffuses into the blood and carbon dioxide diffuses out, ready to be breathed out again.

I hope you got all of those correct.

Let's move into the second part of the lesson then where we focus in on exhalation or expiration.

So here we are with our lungs again.

And I want to highlight that exhalation or expiration is the process of breathing out air.

And we do it by reducing the lung volume.

So the little green arrows there are showing that the diaphragms are moving up into that dome shape that we can see, and the ribs are moving down and in.

And as a consequence of that, there is a decrease in volume in the chest cavity, which increases the air pressure inside the lungs and that forces air to flow out.

Imagine that it's almost a bit like a tyre.

If you've got a tyre and you pierce a hole in it, the pressure of air inside that tyre is much higher than the pressure of air outside.

So the air will rush out until there's an equal pressure inside the flat tyre and outside in the atmosphere.

And that's kind of what we're doing here with the lungs.

We're decreasing the volume to force air out.

So to have a look at the pathway of that then.

So we've got air containing a decreased percentage of oxygen and an increased percentage of carbon dioxide that we want to get out of the body.

And we move it from the alveoli to the bronchioles, from the bronchioles to the bronchi, from the bronchi to the trachea, that windpipe of the middle there.

And then from the trachea out through the nose and mouth.

And particularly during exercise, we tend to breathe out more through our mouth, don't we? To try and get bigger volumes of air in and out actually.

So it goes out into the atmosphere.

And then we want to get another fresh breath in of new oxygen-rich air.

So let's do another quick check.

Which of the following happens when we breathe out? Is it a, the diaphragm returns to a flat shape? Is it b, the ribs move up and out? Is it c, the chest cavity increases in size? Or is it d, the diaphragm returns up to a dome shape? Have a little think.

That's right, it's d.

So when we breathe out, the diaphragm returns up into that dome shape.

Well, Sam's wondering, can we repeat that process and draw a flow diagram of exhalation and what that looks like? Well, yeah we can, can't we? So the intercostal muscles relax.

And that causes the ribs to move down and in.

At the same time, the diaphragm is relaxing up into a dome shape, which causes the volume of the lung cavity to decrease.

So we've got less volume and smaller size, which causes air to rush out because of that increased air pressure.

So air rushes out of the lungs.

Another quick check.

True or false? We breathe out more carbon dioxide than we breathe in.

That's right, that's true, isn't it? And it's because carbon dioxide is a waste product of respiration.

So we extract oxygen from the air that we breathe in, and we use that for aerobic respiration.

So to provide energy for our muscles to contract, and we replace it with carbon dioxide, which we will then breathe out.

When we exercise, this gaseous exchange happens more and more and faster.

Okay, let's go into the second task of today's lesson then.

So I'd like you to explain what happens to get carbon dioxide from the bloodstream out of the body.

So this is almost like that first task that was all looking at inhalation, but this one is looking at expiration.

And instead of being a gap fill task, I've just provided you with a word bank, and I want you to build your own sentences to fit all of these words in.

So how does carbon dioxide move from the bloodstream out of the body? So you're gonna need to pause the video now.

This one will take a little bit longer to complete, but come back to me when you are ready.

Okay then, so I wonder if you came up with something similar to me.

So I've said that the intercostal muscles relax and that causes the ribs to move down and in whilst the diaphragm also relaxes back up into a dome shape.

This decreases the volume of the chest cavity, which increases the air pressure and hence initiates exhalation, also known as expiration.

So those words are used interchangeably.

Then got on to say that gaseous exchange happens at the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out, ready to be breathed out.

So carbon dioxide rushes from the alveoli up through the bronchioles, to the bronchi, to the trachea, and then from there, it exits the body through the nose and mouth.

How well did you do with that one? Quite an extended answer that you needed, wasn't it? Okay then, let's move into the third part of this lesson.

At the very beginning, you'll remember I asked if you knew what spirometer meant.

Well, this is our opportunity to look at some lung volumes and theses spirometer traces that are taken.

So did you know that at rest, we breathe in or out about 12 to 20 times a minute? And this is known as your breathing rate, or your BR, or your frequency of breathing.

But also did you know that during each breath, we're exchanging an amount of air? And at rest, each breath brings in about 500 millilitres of air into the lungs and enables gaseous exchange to happen.

That volume of air that enters the lungs during inhalation is known as tidal volume.

So we call it tidal volume 'cause it kind of comes in and out and in and out.

And that tidal volume of about 500 millilitres.

So that's kinda like a Lucozade bottle size volume of air is coming in and out of the lungs in each breath at rest.

Obviously, the bigger your lungs are, the bigger that will be.

And the tidal volume repeats every breath.

Okay, so to expand the lungs more during exercise because we know during exercise, we wanna get more oxygen to the working muscles.

So we want to breathe more, but we also want to breathe deeper.

So to expand the lungs more during exercise, some additional skeletal muscles are recruited.

Where do you think some muscles are that could help pull your rib cage up and out? Yeah, so it's the pectorals.

So your pecs are able to help pull that ribcage up and out.

But also, there's some muscles in your neck here that are called the sternocleidomastoid.

Great word that, isn't it? The sternocleidomastoid.

And those neck muscles also help open up those airways to get more air into the lungs.

Meanwhile, if we wanna breathe out, during rest, that's a passive thing.

So if you take a big breath in everybody and then just relax, your ribs will just, with gravity, slowly move back down.

But during exercise, we want to get that air exchange happening faster so we can get more oxygen into the body and more carbon dioxide out.

So during exercise, we force that air out.

So take a big breath in, everybody.

(Mr. Schweiz inhales) And then blow out and have a feel where is there some muscular contraction going on? (Mr. Schweiz exhales) And hopefully, you felt your abdominals, your six-pack contracting to help pull that rib cage actively down and in quickly.

So the more you exercise, the more you'll also be exercising your abdominal muscles.

And then that spirometer trace I mentioned.

So that's a graphical representation of the volume of air that someone breathes in and out over time.

So it's a little bit like, you've probably seen heart rate monitors on people when they're in the hospital.

Well, this is, spirometry would be with a mask on your face, taking that air pathway in and out.

So we've got the tidal volume there, that little wave, and that will keep going like that.

But if you were to breathe more air in, so let me take a normal breath in.

(inhales) And then I've taken an extra breath in.

We call that the inspiratory reserve volume.

So that's that extra amount of air that you can breathe in on top of a normal breath in.

And then if I take a normal breath out, I can also blow out some extra air (exhales) to fully deflate my lungs, and that's called the expiratory reserve volume.

But even when I've blown out as much air as I can, there is still a residual volume of air that's kept in the lungs that stops them from collapsing.

And if you imagine blowing up a balloon, you'll be doing maximum inspiration, so using that inspiratory reserve volume and blowing out as fast as you can to the end of your expiratory reserve volume.

And that's a much bigger volume of air than your tidal volume.

And when you start to exercise, I guess you work somewhere up between the two.

So your tidal volume gets bigger up closer to that maximum volume of air that you can exhale.

That's actually called a peak flow monitor that you can use to figure out what your maximum volume of air you can force out is.

So on this graph, we can see the tidal volume, that wave there that would keep going.

We can see that inspiratory reserve volume, and we can see the expiratory reserve volume but also that residual volume.

Okay, so to help you understand the different lung volumes, I want you to take a normal breath in, i.

e.

, your tidal volume and then see how much extra air you can breathe in by fully expanding your lungs.

So this, as I said, is known as your inspiratory reserve volume.

So you breathe in.

(inhales) How much extra air can you get in? And when we exercise, we'll breathe deeper and start to use up some of that inspiratory reserve volume.

Hence, why it's called a reserve volume.

Can you do the same but with the expiratory reserve volume? So you would take a normal breath out, and then force out as much extra air as you can from your lungs.

So, (exhales).

As I said, that's like an example of blowing up a balloon.

You force out air as fast and hard as you can.

What muscle did we say is used to help force that air out? That's right, it's the abdominals, isn't it? And I've got a really nice illustration here that you might have seen in science actually that shows that movement of the diaphragm.

So as that person's pulling on that sheet at the bottom, that's replicating the diaphragm, and you can see the balloons that are representing the two lungs are inflating when that gets pulled down due to those pressure changes inside the lung cavity.

So there we're seeing inhalation or inflation and deflation of the lungs as the diaphragm moves.

But there's always a residual volume in those lungs, and that stops, almost a bit like a balloon.

It stops the sides from sticking together.

If you've got a brand new balloon, you have to stretch it a bit, don't you? And get the sides loose from each other.

Well, once you've blown them up once, they're much easier to blow up the second time because they have this a bit of residual volume in a balloon.

And similarly out lungs always want a little bit of residual volume in them.

As I said, the harder you exercise, the faster your breathing rate gets, but also the bigger your tidal volume of air flowing in and out of the lungs will get.

So let's do another quick check.

Which of the following is a measure of the extra volume of air that can be inhaled after a normal breath in? So a, tidal volume, b inspiratory reserve volume, or c, expiratory reserve volume.

That's right, it's the inspiratory reserve volume, isn't it? And that brings us nicely into our last task for this lesson.

So I'd like you to have a go at labelling lung volumes a, b, and c on this diagram.

And then I want you to write an explanation or a definition of each, and then an explanation of the effects of exercise on each of them.

Pause the video now whilst you do that, and I'll see you in a moment.

Okay, let's see how you get on with that one.

So A is the inspiratory reserve volume, B is that expiratory reserve volume, and then C is the residual volume.

Did you get those three correct? And then the harder task was coming up with a definition and explanation for each and the effects of exercise on them.

So the inspiratory reserve volume is that additional volume of air that can be forcefully inhaled after a normal inhalation, and it decreases during exercise 'cause we start to use up some of that reserve.

B is the expiratory reserve volume.

So that's that additional volume of air that can be forced out after a normal exhalation.

Again, it decreases during exercise 'cause we are using up more of that volume to get more air into our lungs per breath and more air out of our lungs per breath.

And then C, the residual volume is that volume of air that remains in the lungs after maximal exhalation.

And that stays there all the time.

So during exercise, the residual volume is the one that stops your lungs from collapsing.

How did you do with that? Okay then, so let's move on to a quick summary.

So this lesson around the mechanics of breathing, we looked at how inhalation uses the intercostal muscles and the diaphragm to contract and expand the chest cavity volume, which causes air to rush in because the pressure in the lungs has decreased.

Then we looked at exhalation at rest and how the intercostal muscles relax, which makes the rib cage move down and in and the diaphragm returns up to its dome shape, which means air is expelled.

We talked about how the tidal volume is the amount of air breathed in or out per breath and typically about 500 millilitres.

And then we said that when we exercise, the pectoralis major or the pectorals and the sternomastoid, that fancy word for the neck muscles, they also contract to expand the lungs more during inspiration.

And the abdominals also contract to help speed up expiration and pull the ribs down and in.

We also looked at a few spirometer traces, didn't we? And we know that they are a graphical representation of lung volume changes over time during breathing.

Hope you enjoyed today's lesson.

There was lots in there again, wasn't there? So I look forward to seeing you again next time, and well done for today.