We have been dealing with the laboratory techniques
quite a bit. And what we are doing here is
making sure that we know as to who is coming
in and how to properly assess the information
that’s going to come at you. At
this point, you should be extremely
adept at being able to delineate as to when
test is used when and for what reason. So,
on that note, let’s begin by looking at
pulmonary function tests.
Conventionally speaking, pulmonary function
tests are used so that you can divide your
obstructive versus restrictive lung diseases.
With your pulmonary function tests and the
type of graphs that we are going to create,
you will see that you can get a heck of a
lot more information out of it and what is
expected of you at this junction in your medical
education because of the evolution of the
boards themselves. You will enjoy this because
it’s building upon things that you already
Now, the three main categories of the testing
include the following. We’ll take a look
at spirometry, of course, which is probably
the most famous of them all. And with this,
it’s the ratio of FEV1 over FEC that we
will take a look at. What does it actually
mean? It means the amount of air that you
are able to get out in one second, forced expiratory
volume, one second, over the total amount
of air that you physiologically are able to
get out which is only limited by, what volume
please? Good. Residual volume. You cannot
exhale your residual volume completely.
Now, if it is obstruction, what does that
even mean to you? It means that you cannot
properly get your air out. You are obstructed.
When that occurs, well, what kind of changes
are we going to see? We will take a look.
Must have a decrease in vital capacity and
a decrease in total lung capacity for diagnosis
of restriction. That is important and we will
focus upon that. The obstructive part is quite
simple. The obstructive means that, for the
most part, I cannot significantly exhale.
So, FEV1 is going to drop dramatically and
you find that, well, for VC and TLC that for
the most part, that will be a little bit different.
In restrictive, both VC and TLC must be decreased
in order for you to diagnose restrictive.
You will see why. What kind of lung volumes
become important for us, clinically? Total
lung capacity and residual volume.
As I told you earlier, there is no way that
you can possibly measure residual volume.
You must have a little bit of your air inside
my lungs so that it does'nt collapse. Remember,
it is always going to be at negative pressure.
And that has to be kind of balanced by the
fact that the chest wants to recoil, right?
And so, therefore, that negative pressure
has to remain and if you lose your air completely,
well, that ends up being a problem and obviously,
we will talk about that later. And blood
or body plethysmography, in other words the
"body box”, is really the gold standard for
measuring the lung volumes. Plethysmography.
The other tests that we will take a look at
is the diffusion capacity for carbon monoxide,
and we will call this DLCO. Now, please understand,
carbon monoxide is used for different reasons
in pathology. Carbon monoxide, here, clinically,
will be used to see as to how quickly, this
is by proxy, by proxy, you will utilize carbon
monoxide to see as to how quickly it then
diffuses across that membrane into pulmonary
capillary. So, therefore, it is a good measurement
of gas exchange. This does not mean you take
a patient’s mouth and put it over a car
exhaust. That is not very nice. Nor are you
going to do that. This is just a little bit
of carbon monoxide for diagnostic purposes.
Now, if by chance there was a patient who
got exposed to carbon monoxide from a car
exhaust in a closed environment, granted garage,
but more importantly, as to what occurs on
a regular basis. We will talk about
this later, especially during the winter,
where there might be fumes and gases coming
out of in the basement heater, what not. Or
maybe those of you that enjoy the sport of
hockey. And sometimes, you know, it gets cold
in there and so, people that work in those
ice rinks accidently leave their car on in
a closed environment and anyhow, that is carbon
monoxide poisoning. You see the difference
now? This is only for diagnostic purposes.
Both have heavy relevance for you and when
the time is right, we will look at both.
Let’s take a look at an overview
of your lung volumes and capacities. I will
only focus upon the ones that you need on
this graph. Clinically, this is obviously
from physiology. So, begin by looking at
tidal volume. Right there in the middle there,
looks like a waves that are really tiny
and that’s your tidal volume. See labelled
as such, at the end of the graph there. The
tidal volume does not require any effort.
It’s a fact that it’s quiet inspiration,
quiet exhalation, that’s it. It’s approximately
about 500, keep that in mind. As
as we go through this, like we have
been doing, there is going to be a lot of
physiology involved only because we need to
have this for clinical reasons. And then,
well, that should go into breathing with inspired
or great effort is then known as your inspiratory
reserve volume. And once you go below your
tidal volume with expiration, that is then
known as your expiratory reserve volume. And
so, some of these volumes that are important
for us, however, include the following.
Residual volume. That is the last bit of air
that we have in the lung that you cannot properly
void. There is no way that you can do that
on spirometry, but some of those volumes that
we talked about with the body box and such
might help you figure out your residual volume.
Next, the type of volume is the tidal volume,
we looked at it. And then the capacities.
The capacities that are important
for us include vital capacity. Take a look
at vital capacity, Includes everything except
our residual volume. Vital capacity is important
for us because it then explains forced vital
capacity. That is part of our pulmonary function
test. And it is not really timed in terms
of exhalation. The other big capacity that
we need to take a look at is function residual
Functional residual capacity is more or less
your control point. So, for example, when
you have done your graphs. Your graphs, known
as the-the graphs for inspiration-expiration,
and the functional residual capacity be
the control point, a ground zero in which,
for example, if it is obstructed lung disease,
then FRC is increased. If it is restrictive
lung disease, FRC is decreased. We will talk
more about that later. Total lung capacity
is important for us. For example, here, a
large lung, say that you see a huge lung on
your AP diameter and also on your chest x-ray
from anterior posterior, you find that there
is a huge black areas of the lung where the
diaphragm has then been pushed downward. That’s
emphysema that I am referring to bilaterally.
And there you can expect your total lung capacity
to be increased. Okay, so those are some
important volumes and capacitities that you
want to keep in mind and that will be good
enough for you to at least know what is
going on clinically. Let's continue.
Spirometry, what the patient doing? Takes
a deep breath and then begins breathing out.
That breath which is then coming out at one
second is known as FEV1 and the forced vital
capacity is the air that you are getting out
without being timed. The ratio here of FEV1
over FEC ratio should be approximately 0.8.
Now, if there is obstructive, what does that
mean to you? Difficulty with getting air out,
then you can only imagine which one of these
parameters of the ratio has been affected
severely. It’s your FEV1. Your FEV1, the
amount of air that you are able to get at
one second is severely obstructed. So therefore,
you expect your ratio to decrease and that
would give you something dramatically less
than 0.8, 0.7. You are on the side of getting
less, may be 0.3, 0.25. Without a doubt, your
diagnosis, obstructive category. Your next
step after you put yourself into obstructive
category is to figure out which of the four.
Is it emphysema? Is it chronic bronchitis?
Is it bronchiectasis? Or is it asthma? And
that part becomes fun.
Restrictive. What does this mean? Well, let
me put this out here. Please understand that
with any type of lung disease, your FEC is
going to be decreased. "But, Dr. Raj, you just
said that the ratio is decreased with obstructive."
Exactly, that is true. But your FEC is decreased,
but who is decreased even more so? There you
go. Your FEV1. That is the quantitative dramatic
decrease that truly decreases the ratio. I
don’t care what kind of lung disease, your
FEC is always going to be decreased. Then
what is it that determines the ratio? The
FEV1. Do not get your vital capacity confused
with functional residual capacity. Is that
clear? Functional residual capacity is this,
at control. Let me demonstrate. Well, actually
I cannot, I will kill myself. I will sacrifice
myself for medicine, but I am not ready to
completely give myself up. But anyhow, point
is, theoretically, FRC is your epiglottis
open with absolutely no air moving in and
out. I could try, but I think I would just
look really bizarre. So, that is your theoretical
FRC, ground zero. And do not get your FRC
confused with FVC. And in any lung disease,
FVC will be decreased.
In obstructive, what is my FRC? Increased.
Good. What about restrictive? What is my FRC?
Decreased. I hope that is clear before moving
on. If not, make sure you know your definition
for some of these capacities that we have
been talking about. Now, restriction is suggested
by low FVC. Okay, fine. So, why is it that
the ratio is either normal or perhaps even
increased in restrictive? Because the FVC
might be decreased, but FEV1 is definitely
not as decreased as what we found in obstructive.
So if that's the case, then please understand
as that, well, you have a higher FEV1 number.
You can actually have PFT, pulmonary function
test, and its percentage being greater than
80%. So, I can say this to you factually that
you will never, in restrictive lung disease,
have a decreased ratio. I can tell you factually,
that are both obstructive and restrictive
will have a decrease in FEC. Is that clear?
So, restriction is suggested by low FVC, but
needs lung volumes testing to confirm because
the residual volume is not measured by spirometry.
So, confirmation comes from the fact that,
well, you need to see as to whether or not
residual volume or you tell me. Do you think
residual volume is increased or decreased
if we are dealing with restrictive? Give yourself
one big example. A fibrosed lung. That is
a lung that is absolutely non-compliant. It
is very stiff. You can expect total lung capacity
and you can expect your residual volume to
be decreased in restrictive. Clear?
For example, spirometry may show the findings
of obstructive, but the decreased vital capacity.
This could mean two possible clinical outcomes.
What does that mean? For example, let’s
do scenario A. CO, stop there, obstructive.
What does this mean to you? You know that
you have a severe decreased in FEV1. Your
FEC is decreased, overall the ratio is decreased.
You know that the TLC is increased and you
know that your residual volume is increased.
Now, COPD patient experiencing super imposed
restrictive, stop there. Is that common? Yeah,
it is. So, COPD experiencing superimposed
restrictive disease, in which case the lung
volume, the TLC, will also be decreased. Amazing,
huh? So now, you have patient with spirometry
that is now shown to have a decreased FEV1
to FEC ratio. But then all of a sudden,
guess what? You need to further diagnose.
Now that you start seeing your lung volumes
and TLC being decreased, chances are pretty
good that your patient with an obstructive
disease had a superimposed restrictive. Fascinating,
isn’t it? Exacerbations are always taking
place. Do not forget that.
What about scenario B? A COPD patient experiencing
decreased VC. Okay, we know that. Due to hyperinflated
lung trapping, without a superimposed
restrictive condition. Therefore, what happens?
Ah, confirmation by an increase in lung volume
of TLC. So, priority number 1, confirm obstructive.
You got yourself a decreased ratio. Fantastic!
Well, you never know. There could be super
imposement of restrictive disease, hence the
lung volumes. In your particular case, may
be you only need to go as far as obstructive.
However, be careful, because you are going
through answer choices and you do find
restrictive disease, see to make sure that
the lung volumes correlate with your initial
diagnosis. 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.
Other important patterns that you want to
keep in mind. You will like this. Watch. The
first one is called fixed obstruction. What
does this mean? Well, this could mean that
first and foremost, let’s begin the same
The loop spirometry, different pathologic
patterns that you are responsible for understanding.
We will begin with residual volume. Okay.
Does this-Does this even look normal? No,
it doesn’t. Actually, the both, the
bottom half and the top half look like they
are kind of sandwiched, isn’t it? It looks
like a-a burger, doesn’t it? Looks like
buns. That’s what it looks like. And that
black line in the middle, that is your piece
of bacon. I don’t know, whatever. So, the
point is they are compressed. What happened
here? There is difficulty with inspiration,
hence flattened and there is also difficulty
with expiration. What the heck kind of disease
is going to give you a fixed obstruction?
A ENT tumour. In other words, you have
perhaps dangerous, a head and neck type of
cancer. When there is a head and neck type of tumour,
cancer, this is then causing a fixed large
obstruction of both inspiration which is the
bottom half of the curve and the top half.
That is fixed. Let's move on to another
Now, first and foremost, dissect the curve,
interpret this. Where is my problem, please?
Inspiration? Exhalation? Good. Inspiration
only. You see that there is only a problem
with inspiration. Wow! What the heck kind
of problem or disease of pathology has given
me a problem with inspiration only? The problem
is extra thoracic pathology. Meaning, maybe
with the vocal cords. So, with the vocal cord
type of dysfunction or maybe perhaps fibrosis
or an upper airway mass, this is the most
tested, well, please understand, that you
are going to have a hard time inspiring. Is
that clear? So, therefore, the bottom half
of the curve has not been affected. But, you
do not have problems at getting the air out.
This is not, I repeat, anything to do
with obstructive in terms of the pulmonary
issue. Obstructive here, I wouldn’t even
use this word. I would just think of this
as being inspiratory issues.
Now, we do think about obstructive. I want
you to keep the theme of obstructive and inside
the lung. First and foremost, interpret the
curve for me. Where is my problem? Good. The
top half. What does that top half represent?
Exhalation. Interesting! Earlier discussion,
I just showed you obstructive lung disease
with scalloped type of second half of exhalation
with a left shift, meaning to say, an increase
in TLC. That was obstructive. Here, please
understand, when you have such a obstructive
pattern, that you will see at some point in
time, that this is a problem inside my lung
and this will be something like obstructive
disease, or but also, intrathoracic tumour
whereas the tumour in the first one, fixed.
Where was it? Oh, ENT. Ear, Nose, Throat.
Clear? Blocking, fixed. What was the one with
extrathoracic? That was vocal cord, problem
with inspiration only. More common than you
think, especially in health care workers.
Vocal cords often times, often times damaged.
Now, under the three main categories, take
a look at lung volumes. TLC, residual volume,
and once again, the Gold standard here
for measuring lung volume will be a body box,
plethysmography. Lung volumes used in measuring
residual volume, we talked about that spirometry
cannot, report’s out, your TLC and vital
capacity will be two big ones. Then reduced
TLC seen in what kind of disease, please?
Good. Restrictive. Elevated TLC and residual
volume will be seen in what kind of disease,
please? Good. Obstructive. We will call this
Our third and final category, extremely important,
diffusion capacity carbon monoxide. What does
this mean? As I said, you are not taking your
patient and putting them on a car exhaust.
No, be kind. You are going to give just enough
carbon monoxide in which you are then going
to measure for how quickly, does my oxygen,
by proxy move into my capillary.
Why don't we just use oxygen? Because
it’s so slow. Okay? Carbon monoxide, boom.
It’s like 20 times quicker to diffuse across.
Not to mention, carbon monoxide is highly,
highly and has great affinity to haemoglobin,
doesn’t it? So, all these things make it
very, very important to use carbon monoxide
and to test your diffusion.
Now, what does that even mean? Be careful
here because this is how you interpret it.
That is all fine and dandy. You got the facts
down, but what does it actually mean in terms
of test? If your DLCO is decreased, meaning
that the ability for this oxygen to diffuse
across your membrane has been compromised,
your DLCO will be decreased. Clear? For example,
say that you have increased barrier between
the alveoli and into the pulmonary capillary.
An increased barrier. Give me a pathology,
in general. Good. Fibrosis. What if you have
left-sided heart failure? What is the barrier
now? Oh, it’s fluid. What do we call this?
Pulmonary edema. Now, if you have such a barrier,
first and foremost, tell me about that A-aO2
gradient that we talked about earlier. Air
is stuck in my alveoli, the diffusion goes
down, my little “a” is going to further
decrease. You can’t properly diffuse. A-aO2
gradient, widened. Now, next, I just gave away
the magic statement. Increased thickness,
decreased diffusion, you expect your DLCO
to decrease. Clear? That is your best example
there. Let’s take a look.
It can be reduced because of surface area.
Who is? DLCO is, diffusion capacity carbon
monoxide. Why? In emphysema, I thought, I
thought, I thought, hold on. You might have
thought that it was increased compliance and
therefore, makes it easier. No.
Granted, emphysema is a very compliant lung.
It wants to expand like crazy, but how much
damaged you have your parenchyma? Quite a
bit, huh? So, what happens to the surface
area? Decreases. So, when you lose surface
area, can you have proper gas exchange? Of
course, not. That’s why you have COPD. That’s
why you have a decreased DLCO. Let’s continue.
When else could it be decreased? Oh, there
it is. Greater barrier to diffusion including
fibrosis or maybe pulmonary edema. But, there
is one big exception that I need to give you.
Let's just say, I will just put it out there
for now. The one big exception will be alveolar
haemorrhage. Is that clear? You will see why.
Next, sometimes increased in asthma. So, what
does that mean, when it increases? It means
that the oxygen is travelling across that
membrane very quickly. Early on in asthma,
what could the patient be doing? Breathing
a little bit faster because of asthma and
if there is proper gas exchange, they might
actually increase the gradient. And therefore,
oxygen might get across as the membrane very
quickly. There might be an increase in DLCO
or to asthma, keep that in mind, please, when
you are reading a stem of any type of clinical