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 FVC 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, 0.7. You are on the side of getting
less, may be 0, 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 FVC is
going to be decreased. "But, Dr. Raj, you just
said that the ratio is decreased with obstructive."
Exactly, that is true. But your FVC 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
FVC 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 FVC. 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
FVC 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 FVC 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