Let’s take a look at a important
pulmonary function test and loop spirometries
that are relevant to your clinical understanding.
Let’s take a look at the normal one first,
right smack dab in the middle. Let's make
sure, please, that we are absolutely confident
about what the loops mean. What Y-axis, X-axis
and the top and the bottom portion of the
loop means. Let's begin. In the middle there,
is normal. Next, well, what does that
X-axis represent? Well for the most part,
your volumes. I mean to say, well, how much
is your lung filled with air? Let’s put
it that way. You notice your residual volume
and that will never change. You see the lines
in blue, dashed line? That is residual volume,
that is the air that is always going to be
present normally in your lung, has to be.
Next, well, as you move in the middle from
0, 2, 4, 6, please understand, that is, take
a look at the end on your right, the X-axis
is labelled as volume. Keep it simple. So
as you move from right to left, from 0 to
6, that obviously means an increase in volume.
Hmm, interesting! So, which one of these.
which half of this loop represents inspiration?
Please, please understand, it’s the bottom
loop entirely. The entire bottom loop, from
the beginning where it’s between 0 and 2
moved all the way up to 6, represents inspiration
only. All of it. Stop. So now, you have ended
at TLC, total lung capacity. That is full.
Okay. Now, where do you gonna begin? Well,
let’s go through some physiology. Where
is my diaphragm? Oh, it’s passively moving
up. Good. Passively moving up. Now, what happens?
Oh, the alveolar pressure is becoming positive.
What does that mean? It’s going to squeeze
the air out through the alveolar ducts, moving
it out. Good. What happens to your pleural
pressure? The pleural pressure is becoming
less negative, isn’t it? So, maybe it was
at negative 8, now it’s moving down from
negative 8 to negative 7, negative 6, negative
5 and then you have the recoil or elastic
pressure, right? And that elastic pressure
is becoming well, equivalent. Equivalent to
your pleural pressure. It has to. So, this
is the process of expiration that you should
be oh so comfortable with before we move on
to the exhalation aspect of this curve.
There are three different things that are
going on. There are three different pressures
and please understand, at the end of expiration,
we have now once again reached FRC technically.
At the end of inspiration, we have now technically
reached FRC. That means now the alveoli is
filled. Where am I? At 6. You picturing this?
Alveoli is filled with air and its pressure
is pretty much equivalent. It’s at 0. FRC.
The pleural pressure and the recoil pressure
are both equal at approximately 8, shall we
say. They are going to begin the process of
expiration. Here comes the air out. The entire
top loop, ladies and gentleman, represents
expiration. You will divide this into the
first half of expiration upon the top loop
and the second half of expiration, exhalation.
Now, during exhalation, the second half, wow,
there isn’t as much air than coming out.
Hmm, what does that mean? Think about that.
As the air is coming out, then there is more
pressure for it to close. So therefore, this
is called dynamic airway expression. So that
dynamic airway type of expression takes place
usually the latter half of exhalation. This
then brings us back to, well, where we started
at? And you will notice here ladies and gentleman,
that there is still little bit of volume left
and that is your residual volume. This is
a perfectly normal loop spirometry.
Let's go to our first pathology. You will
find that the pulmonary function test in FEV1
to FVC ratio is less than 0.7 or 0.8 and it’s
at 0.3. This to you without a doubt means
obstructive. No doubt, no doubt. What you
need to confirm that it’s only COPD or that
it’s only obstructive? The volumes, right?
So, they will tell you that the volume, meaning
the TLC is increased or they show you loop
spirometry here. So, on your left is obstructive.
How can you confirm that? Well, for two reasons.
Number 1, the red loop represents the normal
loop spirometry. What’s inspiration again?
The bottom half of the loop. Inspiration has
taken place, it is leaves you to 6. I told
you with that type of pulmonary function test
that you have a ratio that is less than 0.3
or its at 0.3. Then where is the air trapped?
In your lung. Think of emphysema, that is
your best one. Emphysema, the lungs are getting
bigger, are they not? It’s a PA and AP everything
shows increased diameter. There is going to
be bilateral compression or depression of
the diaphragm. And what about TLC? It was
a 6. Oh look, it’s moved to the left. Now,
it’s moved up to 8. No doubt now, that
with the combination of ratio being decreased
and TLC increased, confirmation of obstructive
only without any super imposed restrictive.
Is that clear?
Next, I want you to begin the process of expiration.
Expiration has taken place the first which
is only the top half of the loop, the
green curve, the top half and then you find
that there is indentation. The scalp portion
there represents, dynamic airway compression.
Very quickly the airways, do they want to
collapse. You got a problem. The air does
not want to come out.
Next, I want you to take a look at the residual
volume. Is the residual volume in the
normal? Take a look at the residual volume
here. A lot more volume stuck in your lung.
Obstructive, you can’t miss it. Now, let's
go to the other side, shall we? Let me give
you an example, pathological condition, there
is a bunch with restrictive. These include
interstitial lung disease which we shall categorise
properly. When you think interstitial lung
disease, you should be thinking about for
whatever reason, there is fibrosis taking
place in my interstitium. Clear? What else?
Maybe pneumoconiosis. What are pneumoconiosis?
Or maybe your patient was exposed to coal, asbestos,
silica, berylliosis. My point is, there is
a bunch of differentials for restrictive.
At this point, you find that the FEV1 to FVC
ratio is normal at 80%. Interesting! But
yet your patient was exposed to coal? Wow!
And I find that the chest x-ray that it’s
a reticular pattern with mesh work. Okay.
So, now, what are you thinking? Maybe, most
likely, restrictive. Once again, the normal
would be the red loop. Now, you have a very
fibrosed lung and we will talk about this
as being a worst case scenario, progressive,
massive fibrosis with a very non-compliant
lung which is stiff. Please understand that
you don’t have any problem getting here
in, but you only get a little bit of air in.
How can you confirm that? Take a look. You
only moved up to approximately, well, little
bit less than 4, may be only up to 3
litres. Normal is up to 6. So, tell me about
your TLC. The original TLC was 6, it has now
moved down to approximately 3. No doubt, your
FEV1 to FVC ratio being normal only suggestive
and with that history and the lung volume
and TLC being decreased, has to be restrictive.
Are you seeing this? Let's continue.