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.