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