welcome to another MedCam 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 that'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 or 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 gonna 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 if you've got somebody
here who is very tall versus somebody who's very short obviously a proportion
of their body is going to have lungs in them and the short person's 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 and 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 we're going to need to know and put into
our equation to figure about what the normal lung volume should
be for somebody number two is good 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
gonna 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 mens
going to have smaller lungs than would white man 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 gonna
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 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 80% limit
is that number there will tell you if you are below this number okay actually
it'll be down on this side here 80% 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 in 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 leaders that means that
the 80th or the minimum 80th percent for three liters or 80 percent of that
predicted is good 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 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
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