Pulmonary Function Test (PFT) Remastered – Procedure, Spirometry, FEV1


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