Pulmonary Function Tests – PFT Interpretation Explained (Pulmonology)
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Pulmonary Function Tests – PFT Interpretation Explained (Pulmonology)

November 17, 2019


Okay so based on everything that we know
now we’re gonna go ahead and show you how to interpret PFDs first thing you
want to do is you want to look at the F the C and you want to see whether or not
it’s greater than 80% of predicted that’s the this is the first thing that
I look at and you really want to look at just any FEC if any FEC is greater than
80% of predicted the answer is yes or if the answer is no and this is the
algorithm that we’re going to look at here if the FEC is greater than 80% of
predicted then what you can say here is that you have no restriction no
restriction and that’s our first diagnosis that we can come up with right
off the bat if however the FEC is less than 80 percent of predictor or the
answer is no then we can say that we either have restriction or obstruction
with air trapping okay so it’s one or the other restriction or obstruction
with air trapping the next thing you do in either one of these cases as you move
on in this case you’re going to ask the question is the fev1 divided by the F
the C greater than 0.7 and again you’re going to have a yes and you’re going to
have a no if the answer is yes then there is no obstruction so by definition if the fev1 divided by
the FEC is greater than 0.7 there is no obstruction if however it’s less than
that then you have obstruction okay the next thing let’s go back here if the FEC
is not greater than 80% of predicted then you either have restriction or
obstruction with air trapping the next question that you ask in this situation
is is the total lung capacity greater than 80 percent predicted if the answer
is yes then you have obstruction with air trapping if the answer is no in
other words if it’s less than 80 percent of predicted then you have guess why
restriction now there’s something you should know
about in terms of obstruction and the severity there’s different there used to
be gold classifications in terms of Roman numerals they now used severity
and also symptomatology but if they’re ever talking to you about the gold
stages there’s gold stage 1 stage 2 stage 3 and stage 4 and for that we look
at the fev1 only the FEV 1% predicted 1 is 80 to 100 2 is 50 to 80 3 is 30 to 50
and 4 is 0 to 30 it’s also you go right to stage 4 if there is respiratory
failure with an elevated P co2 level the other thing that you should know about
when you have obstruction is you really should be able to classify if there is
reactivity or not and the 80s criteria for reactivity is fev1 or FV c change in
pre and post bronchodilator in comparison to pre bronchodilator of
greater than 12% and 200 milliliters if you don’t have either of those two or if
you have neither of those two then it is non reactive this doesn’t tell you
whether or not you should give Runkel dilators it is helpful though when
telling you whether or not this has if there is reactive Airways disease the
other thing to look at is the DLC o dl c o and whether or not is greater than 80%
of predicted okay if the DLC o is greater than 80% of predicted then you
have normal membrane surface area if it is less than 80% of
predicted then of course it’s abnormal surface membrane or membrane surface
area okay however the next thing to look at is the dlco divided by the alveolar
ventilation and if it is greater than 80% of predicted now remember what we’re
looking at here we’re seeing whether or not the dlco
divided by the Alvar ventilation is still pretty good this is an indication
and distinguishing characteristic between extrinsic and intrinsic lung
disease of course for yes it would be x trinsic and for no it would be in
trinsic so what are some examples this would be like scoliosis or Gyan Bray
syndrome and this would be for instance pulmonary fibrosis or for instance COPD
okay so let’s go over this again if you’ve got a forced vital capacity of
greater than 80 percent of predicted no restriction you can say that right off
the bat then you look at the FE v1 divided by the FEC if it’s greater than
0.7 then no obstruction you’re done you’ve got no restriction you’ve got no
obstruction if the fev1 divided by the FEC is less than 0.7 however then you’ve
got obstruction no restriction let’s go back to the very beginning if you don’t
have an FEC if of greater than 80% are predicted then you could have
restriction or obstructive with air trapping the way you tell the difference
between the two is by looking at spirometry if your total lung capacity
is greater than 80% of predicted then you know you don’t have restriction
going on but it’s more of an air trapping situation and that’s where the
obstruction comes in if your total lung capacity is less than 80% of predicted
then there’s a good chance that at restriction that’s causing both the
total lung capacity to be low and the FEC to be low once you’ve diagnosed
obstruction then you can break it two different severity and say whether
or not there’s reactivity or no reactivity in a separate situation
you’ve got the dlco if the dlco is normal that’s great if it’s not it could
be because of extrinsic disease or intrinsic disease by looking at the dlco
divided by the alveolar ventilation you can make a distinguishing characteristic
once you know if this is extrinsic disease or intrinsic disease you can put
it together with your other diagnosis up above which are in double squares and
figure out which way your diagnosis goes so keep this written down we’re going to
go over some actual examples and we’ll be able to tell what the diagnosis is by
interpreting the PFDs correctly

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