so popular topic of question for exams in sport or pe is spirometry or your ability to
read spirometer traces now in this example here they're looking for a multiple choice
answer which is quite a simple way to get one mark and they could give you it in two different ways
the definition and then you have to give them the key term back or they give you the key
term and you have to define it for them another way is that they actually give you a spirometer
graph or a sperm with a trace and you have to label or annotate or explain what's going on
at different stages of that sprung to read it now for this one before we go into the answer we first
take a look at what the spirometry graph entails and what it can look like so we'll nip into the
whiteboard and if i could draw a very basic graph where on the y-axis x-axis is obviously time and
on the bottom the y-axis is the the fill of the lungs so up to 100 fill down to zero percent feel
fill i'm sorry i should say and this is measured in liters or milliliters uh typically but you
don't really need to concern yourself with that at this point in time so to start with we see
a bog standard breath in and breath out and anything that bounces between these two levels
is known as our tidal volume our tv so our breadth of the volume of air that we breathe
in and the volume of air that we breathe out at rest now if you want to work that out then
it's just the differences in the wave height so you would measure where the graph gets to
on the inhalation measure where the graph gets to on the exhalation and the difference between
the peak and the trough of the wave is the tidal volume the amount of air that we breathe in or out
per breath now if we were to carry this black line on and change it to orange now and we continue
to inspire continue to inhale this is the volume of air that we have that we have in reserves
in inspiration this is what we could additionally breathe in if we needed additional air to enter
our body for either excess oxygen or to get rid of more co2 in the next breath so this extra this
additional volume of air that we could breathe in following inspiration is known as our i r v the
volume of air that we can breathe in following a normal inhalation the same can then be said on the
opposite if i just draw this line all the way back down anything that goes beyond a normal exhalation
i'll put it in red here is our expiratory reserve volumes the volume of air that we have available
to exhale on top of a regular breath out so if we do have a high amount of co2 accumulating we could
exhale an additional volume of air following the normal exhalation that we just experienced
by doing that we also free up more space for the next breath in so if we add onto this graph now
a maximum inhalation following a maximal exhalation what we actually have here is
something known as our vital capacity it's our expiratory reserve volume
plus the tidal volume plus the inspiratory reserve volume gives us the vital capacity it's the space
inside of our lungs that we actually have access to that we can completely empty or completely fill
in any given breath now there will always be a section of our lungs that we can't empty
now there's always going to be a volume of air that resides
inside of our lungs because we haven't got the mechanics we haven't got a mechanism we
haven't got the the structures that can actually compress the lungs to the extent to empty it 100
there's always going to be some left inside of the lungs and that's known as our rv or our residual
volume it's the volume of air that's left inside of our lungs following a maximum exhalation now
this could be from the base of our tidal volume it could be from the peak of our tidal volume
it could be following a maximum inhalation but following a maximum exhalation down to the point
that no more air can be forced out whatever is left inside of our lungs is known as our residual
volume so then the final thing that we do have is the residual volume plus our vital capacity
gives us our t l c our total lung capacity this is the full amount the full liters of air that
we can fit inside of our lungs following a maximum inhalation so we've got our maximum breath in plus
what was already in there to start with gives us our total lung capacity so if we jump back to the
question now which one of these lung volumes is defined as the volume of air left in the lungs
after maximal expiration or following maximal exhalation what volume of air is left inside
it's our r v so the answer for this question would be c our residual volume but as you can probably
work out they could have changed the definition that they gave you to any one of those definitions
associated with the spirometer trace so make sure that you know all of them for your exam
so that any whenever a definition comes up you can give the key term and also if they give you the
key term can you define it in relation to what's going on inhalation exhalation residual volume
etc so that's that hope you found it useful and i'll see you again in the next video