kram welcome to another MedCram
lecture we're going to talk about
pulmonary function testing and this is
going to be over a couple of lectures
we're going to go over the introduction
and give you a little bit of a primer if
you will on pulmonary function testing
and then get into more specifics so that
you understand exactly what it is it's
going on so the whole point of pulmonary
function testing is to measure someone's
lungs and find out whether or not
they're normal or abnormal and if it's
abnormal find out why now this is kind
of akin to getting tests on for instance
your heart with an echocardiogram or an
EKG where we're measuring the heart well
the problem is that the heart is
measured on a proportion for instance
the ejection fraction is how much blood
on each pump the heart can pump out and
normal is you know approximately 50%
ejection fraction and we can measure the
chamber size and we can measure the
valve and see if there's regurgitation
the problem is in taking this issue and
taking it over to the lungs is that the
lungs are more of an absolute and
people's lungs can be different based on
their height and other variables
so we need to figure out exactly how
we're going to figure out what's normal
for somebody's lung and that can be a
little tricky so are there four things
that we need to take into consideration
before we determine what the absolute
values are for somebody who can do a
pulmonary function test and the first
one is height okay so height makes a
difference let me explain
you've got somebody here who is very
tall versus somebody who is very short
obviously a proportion of their body is
going to have lungs in them and the
short person is going to have smaller
lungs and the bigger person is going to
have bigger lungs and so obviously the
amount of air absolutely they could be
able to breathe in
out is going to be dependent on the size
of their lungs so obviously height has
to come into it so that's the first
thing with it we're going to need to
know and put into our equation to figure
out what the normal lung volume should
be for somebody number two is going to
be age what happens as you hit the age
of 25 which is the best that you're ever
going to be in life in terms of your
lung function is lung function generally
is going to decline even if someone has
never smoked and so as you get older the
lung function is going to decline and
depending where you are along that axis
that x-axis is going to determine where
somebody would be normally for any point
along that curve and so age is the
second variable that goes into the
equation the third variable is gender
okay male and female are going to have
different sized lungs and so that needs
to be taken into consideration this is
independent by the way of height so
gender is the third variable that goes
into that and number four is race let me
give an example if you've got four for
sake of argument here you've got a white
man and african-american black man in
terms of where their proportions are
generally speaking the white man is
going to have his waist or his navel if
you will lower down then an
african-american or the black man it
should be higher so given the same exact
height black man is going to have
smaller lungs than would white
and similarly you could look at the
other way that black men would have
longer legs for a specific height then a
white man who would have shorter legs
and this has been looked at and
researched in in the literature and so
as a result race also needs to play a
role in terms of if you have someone
with a specific height they're going to
have different sized lungs based on
proportionality okay so the purpose of
all of this is to come up with a
customized value for each individual
based on hundreds and thousands of
patients and research and distributions
and curves and things of that nature
so if you put a specific human being
okay and the four variables number one
is height number two is age number three
is gender and number four is race and
you take all of these variables of a
person and you put it into the computer
and turn a crank outcomes values x in
this case and it's that number that'll
tell you what the normal distribution
should be so there's going to be a
distribution of patients and it will
tell you what the eighty percent limit
is that number there will tell you if
you are below this number okay actually
it will be down on this side here eighty
percent here if you are below this
number that means you are abnormal these
are all normal patients here okay and if
you are below the 80% of predicted of
that value then that means you are
abnormal let me tell it to a different
way let's say we plug in those four
values and we come up with a number for
the forced vital capacity and we'll get
into these numbers
a little bit and let's say that the
number they come up with for the forced
vital capacity for argument's sake is
three point zero zero liters that means
that the 80th or the minimum 80th
percent for three litres or eighty
percent if that predicted is going to be
2.4 liters and so if you are below 2.4
liters that is considered abnormal
another way of saying it is that if your
value is greater than 80% of the
predicted then you are normal and
there's no problems okay so the key I
want you to get out of this lecture is
specifically the lungs are a organ of
the body the organ of the body that can
change in size and you can get different
values for different people all with
different distributions
based on the four criteria which is
height number two is age number three is
gender and number four is race once you
take an individual and you plug those
numbers into the computer they will give
you values and it's those values that
you must base your abnormals on this is
different than looking at blood tests
for the liver or looking at an
echocardiogram for the heart because in
that situation there really you don't
really have to take into consideration
these values so in our next lecture
we're going to talk about the lung
itself and the pathophysiology but this
is kind of an introduction so join us
for the next lecture thanks very much
you
