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Pulmonary Function Tests (PFTs) | Clinical Medicine — Transcript

by Ninja Nerd · 3,601 words · 522 segments · language en · Watch on YouTube

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0:07what's up Ninja nerds in this video
0:08today we're going to be talking about
0:09pfts pulmonary function test this is
0:11going to be part of our clinical
0:12medicine section if it helps you it
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0:39useful for your academic career all
0:41right let's start talking about pfts
0:42though pfts pulmonary function test it's
0:45not just one test it's a bunch of like
0:47small tests that come together to help
0:49you to discern does this patient have an
0:51obstructive versus restrictive lung
0:52disease and if they do have one of those
0:55which one is it is it asthma is it COPD
0:58is it a ex transic type of of lung
1:00disease for the restrictive categories
1:01is an intrinsic lung disease for the
1:03restrictive categories and it's really
1:04good at sifting that out we'll go
1:06through an algorithm I think that'll put
1:07all this together let's understand it
1:09first so the first thing that you
1:11usually do is you obtain lung volumes
1:13and this can be done via what's called
1:15pmog graphy now what this gives is this
1:18gives you a couple different volumes and
1:20I think it's actually kind of important
1:21to understand this in patients who have
1:22obstructive lung diseases their lungs
1:23are super big so that these big
1:25monstrous hyperinflated lungs their
1:27lungs are super compliant which means
1:29they want to stretch and unfortunately
1:31they're super stretchy and big and
1:33distended because they're hyperinflated
1:35they're obstructing their airways which
1:36causes the lungs to get Dynamic
1:38hyperinflation air trapping because of
1:41that they keep a lot of air in their
1:43lungs even at the end of expiration so
1:45because of that their residual volumes
1:47are relatively high and so can they also
1:50their expiratory Reserve volumes now
1:52there's actually a terminology here
1:55which is the combination of these two
1:56and that's called functional residual
1:58capacity here I'll put that as a little
2:00kind of note here that this plus this
2:02gives you this this is really the key
2:04thing in patients with obstructive lung
2:06disease their functional residual
2:07capacities are like really really high
2:09and that's because they can hold a lot
2:10of air in their lungs after a full
2:13expiratory you know
2:14phase now because they can have a lot of
2:17air in their lungs that remains in their
2:20lungs they don't have a lot of volume
2:22that they can take a deep breath in
2:24above that so imagine take a deep breath
2:26hold it don't expire and then try to
2:28take a deep breath on top of that what
2:30these patients are living with because
2:31of these three things here it makes it
2:34so that the actual amount of deep breath
2:35that they can take in above their normal
2:38title volume is Tiny so they can take
2:41potentially normal to lowest title
2:44volumes but here's the big thing their
2:46ability to take these deep breaths in
2:48are usually reduced and that's one of
2:50the classic things that you'll see in
2:52these patients that hyperinflation leads
2:55to reduct reductions in inspiratory
2:58volumes okay cool what about restrictive
3:02lung diseases and these patients their
3:03lungs are super fibrotic they're stiff
3:06they don't want to expand they don't
3:07have the ability to stretch they're not
3:09very compliant at all their elasticity
3:11is increased and they want to be the
3:13smallest size possible so because of
3:15that they don't keep a lot of air in
3:17their lungs even after expiration so
3:19their Reserve volumes are low their Erv
3:21is low which is the amount of air that
3:22you can forcefully exhale Beyond a
3:24normal tide of volume expiration so
3:27because of that if you take the
3:28combination of the these two and you
3:30look at the functional residual capacity
3:33it's also reduced right so you have a
3:36reduced functional residual capacity now
3:38you would probably think oh okay well if
3:40it makes sense of what Zach said if they
3:41have a low functional residual capacity
3:43they got tiny lungs so they can probably
3:44take in deep breaths no unfortunately
3:46they can't even take any deep breaths
3:48either because it's really hard to
3:49expand those lungs it takes a lot of
3:51effort and they unfortunately don't
3:53generate good title volumes and they
3:55don't generate good
3:57IVs now with all that being said
4:00one of the things that you'll notice is
4:01the combination of all of these
4:04components so the Irv plus the title
4:06volume plus the expiratory reserve
4:07Volume Plus the residual volume gives
4:09you what's called a total lung capacity
4:11the maximum amount of air that these
4:12patients can hold in their lungs in this
4:14scenario it's gargantuous because of
4:16their F FRC so they have a very large
4:19total on capacity and this scenario they
4:22have a tiny little total lung capacity
4:25so their total lung capacity be really
4:26really small now a lot of this stuff is
4:29all right Zach I see a lot of like
4:31abbreviations a lot of different things
4:33is there an easier way to remember this
4:34so in other words Zach if I get a graph
4:36that shows up on my exam or on my pfts
4:38and I'm having to read them as a
4:40clinician how do I determine if it's
4:41more obstructive versus restrictive well
4:44sometimes what they do is they use these
4:45things called flow volume loops and it
4:47kind of takes into consideration all of
4:49these things that we just talked about
4:51so here in black is going to be the
4:53normal patient right and the normal
4:55patient from this inspiration to
4:58expiration this whole component here is
5:02what we refer to as the forced vital
5:04capacity for the normal patient and then
5:08the amount of air that remains in their
5:10lungs right after a forceful expiration
5:14is called their residual volume and then
5:18from here to here is their total lung
5:21capacity this is all in a normal patient
5:24now you take an obstructed patient
5:27what's the characteristic here and these
5:29a s their curve or their flow volume
5:32Loop shifts to the left and when it
5:36shifts to the left look at now their
5:39Force vital capacity so here is the
5:41beginning part of inspiration and then
5:43expiration now their Force fital
5:45capacity in comparison to this one here
5:48if you compare these two so this one to
5:51this one it's reduced in compared to the
5:53normal scenario but look at this crap
5:56here from here to here is your residual
5:59volume
6:00it increases significantly and that
6:03again helps you to remember that and
6:05then finally if we were to take the
6:07combination of these two which is your
6:09total lung capacity it's going to be
6:12increased in compared to the normal
6:14patient look look how much wider that is
6:17so that's one of the big things that'll
6:18help you is total lung capacity goes up
6:20residual volume goes up as a
6:23responsibility of the residual Vol going
6:24up the Erv will also kind of go up a
6:26little bit and so will the functional
6:28residual capacity so they can't taking
6:29deep
6:30breaths now we go to the other patient
6:33with restrictive lungs so here's the
6:35normal from this point here of the
6:39inspiration to this point of expiration
6:42is your Force vital capacity this point
6:45here from the end of the force vital
6:46capacity the amount of air that remains
6:48in is your residual volume and then
6:50again the collection of these two is
6:52your total lung capacity if we look here
6:55at this what we notice from restrictive
6:57lung diseases is that they shift
7:00to the right of the
7:03curve and when they shift to the right
7:05of the curve what does that do their
7:07Force fital capacity in comparison here
7:10to this one will
7:12reduce significantly actually and then
7:16on top of that the residual volume will
7:19go down and then if you look at these
7:22patients total Lo capacities it's so
7:26tiny and that's one of the big things
7:28that you'll be able to obtain from these
7:30patients when you look at their flow
7:32volume Loops obstructed shifted to the
7:34left big residual volumes big total UNC
7:36capacities restrictive shifts to the
7:39right small total Lo capacities small
7:41residual volumes that is the big concept
7:44to take away all right so we perform
7:46this test and we get this it'll help us
7:49to say I'm supporting more obstructive
7:51versus more restrictive let's go to the
7:53next test this is really the hitter this
7:55is the mac daddy of most of the kind of
7:57PFT tests and that's called Force by
8:00ometry what you do is you take an
8:01apparatus you take a deep breath in and
8:04you breathe out as forcefully as you
8:05possibly can and it measures that
8:07expiration at 1 second and throughout
8:08the entire time that you expire and it
8:10gives you this graphical representation
8:12we see here now you get two values from
8:14this and then you can form a third one
8:18is you look at what was the amount of
8:20air or volume that expired on the y-
8:23axis at 1 second and both of these
8:25scenarios look at that was the amount of
8:28volume I expired at one second this is
8:31called the Fe V one F
8:37V1 so that would be the amount of air I
8:40can forcefully expire and this would be
8:41an obstructive patient afterwards and a
8:43restriced patient later right we're
8:46going to look at the comparison here
8:47what do I notice now holy stink and this
8:51patient if I go here and I come over
8:53here their fv1 drops
8:56significantly so they have difficulty
8:58getting air out more particularly within
9:00the beginning of expiration so their F1
9:03is massively massively reduced okay here
9:09I don't notice as much there's a little
9:11bit of a drop off in the fv1 but not as
9:14much in comparison to this one but there
9:16is a little drop off in the fv1 so they
9:18do have a Teensy bit of a difficult time
9:20exhaling in the first one second then I
9:23look at the forced VTO
9:25capacities in the forc BTO capacities
9:28and want to form this to be a little bit
9:30worse just so you don't get confused
9:33here with the graphical representation
9:36okay in this scenario here what am I
9:39noticing well here this is the end point
9:42the maximum point the highest point of
9:44the curve is what we refer to and I'm
9:45going to say it's like right here as the
9:47force vital capacity same thing here
9:49kind of flattens out Force vital
9:51capacity of the normal patient all right
9:53the highest point of the graph here for
9:55the Blue Line will tell me what their
9:57Force vital capacity is and it's right
9:59right here and right here so look at the
10:02actual drop and force vital capacity
10:06between these two so you're getting the
10:08point which one has a worst Force vital
10:09capacity the restrictive patient so they
10:11usually have a very significantly low
10:13Force vital capacity whereas the patient
10:15who has obstructive is not as severe so
10:19with that being said if you're having a
10:21difficult time remember obstructive F1
10:24is the problem restrictive fvc is the
10:27problem then from there take the
10:30ratio if this number is really really
10:34low and this one is just a little bit
10:37low the numerator is super super tiny
10:41what's going to happen to the F1 over
10:42FEC ratio it's going to be low and we
10:45say that low is less than 70% all right
10:51and that would be suggestive of
10:52obstructive lung diseases COPD asthma
10:55bronchia acusis one of those for this
10:58scenario
10:59the numerator is just a little bit tiny
11:02but the denominator is the problem here
11:05that's really tiny what happens to the
11:07overall number it's big you take a
11:10number like this okay number divided by
11:12a really really small number you're
11:13going to get a really big number so
11:15generally these are greater than or
11:17sometimes equal to 70% so they could be
11:20in normal or above normal ranges for
11:23restrictive lung diseases so so far if I
11:26take a combination of these two tests I
11:29will have a pretty good idea if I look
11:31at total L capacity residual volume I
11:34look at Force vital capacity F1 and F FC
11:38I should be able to get a good idea of
11:40whether it's obstructive versus
11:41restrictive lung diseases so if I had a
11:44patient who comes in I get this it shows
11:46shifting to the left High total lung
11:48capacity High functional residual
11:50capacity High residual volume and their
11:52fv1 over FC ratio is less than 70 it
11:54suggests obstructive whereas they have a
11:57tiny total L capacity
11:59tiny residual volume F1 over FEC
12:02suggests it's greater than or equal to
12:0370% it suggests more restrictive type of
12:06diseases then what do I do let's come
12:08down to the next test the next test I'm
12:10going to do is I'm going to say I have a
12:11patient who has an obstructive lung
12:13disease and I want to know is it COPD or
12:16is it asthma in other words is it
12:17irreversible or reversible so what I do
12:20is I give the patient a Bronco dilator
12:22we call this a short acting beta 2
12:25Agonist and what this will do is this
12:27will act on those bronchial smooth
12:29muscles and relax them so in this
12:31scenario look I can't get very much air
12:34out right the f1's probably really low
12:37on this one then I give them a Bronco
12:39dilator opens up the Airways I can get
12:42more air out in the first one second so
12:45I would expect my F1 to
12:48improve after we give them a beta 2
12:51Agonist and if the
12:54F1 does increase that's great but what I
12:59need to know is does it increase greater
13:01than
13:0212% if it does not it's more suggestive
13:06of what obstructive lung disease is
13:10secondary to COPD it's an irreversible
13:13process I take the asthmatic patient I
13:15do the same exact thing I give a short
13:17acting beta 2 Agonist goes and acts on
13:20these bronchial smooth muscles they
13:23super dilate all right now in this
13:26scenario Again difficult to get air out
13:30dilate them woo baby air be flowing the
13:34fe1 should do what it should go up I'm
13:37expiring more
13:38air now if the fe1 does increase by
13:43greater than 12% or at least equal to
13:4612% then I'm more suggestive of a airway
13:51disease that is reactive and can be
13:55reversed all right cool well how do I
13:57even prove this even more more well I
13:59know that asthma is both a kind of Rea
14:01it's kind of a airway disease that is
14:03reversible but also
14:05inducible so in other words I can make
14:07it dilate but I can make it really
14:09really constrict so if I give him
14:11another drug called methine which is
14:13this short acting Bronco constrictor
14:16what would I expect to happen I'd expect
14:19the reverse thing to happen I expect
14:21them to go from having a dilated Airway
14:22to a super constricted Airway and I
14:24expect their F1 to
14:26drop if their F1 does drop I want to
14:30know how much does it drop if it drops
14:33by greater than equal to 20% that's
14:36suggestive of an inducible airway and if
14:39I have both
14:40inducibility right and on top of that
14:43reversibility it suggest asthma much
14:45more so than a
14:47COPD all right once we've done that that
14:49helps us with that scenario but then
14:51let's take it another step we do another
14:52test called dlco testing diffusion
14:54limitation of carbon carbon monoxide
14:56give the patient tiny bit of carbon
14:57monoxide sounds terrible right but it's
14:58not that bad it's not dangerous give a
15:00little bit and you look to see how much
15:02runs through the airway and how much
15:04diffuses across the actual alveoli into
15:07the blood and it'll be dependent upon
15:09how much carbon dioxide is detected when
15:10they exhale so an obstructive lung
15:14diseases what I want to know is what
15:16would actually affect the dlcl with an
15:19obstructive lung disease well osma is
15:21one of those that what it does is we're
15:23going to use this it actually decreases
15:26the surface area right so that's what
15:29obstructive lung diseases would do
15:30particularly empyema it causes alveolar
15:32sepal destruction it gives these big
15:33sucky huge Alvar Airways right or Big Al
15:38Airways because of that the surface area
15:41drops if surface area drops what does
15:43that do to the
15:45dlco directly proportional it should
15:48decrease the
15:50dlco so that would be one thing that I
15:53would be able to see in
15:54osma that I wouldn't really see in
15:57things like asthma I wouldn't really see
16:00this in a chronic
16:02bronchitis well that's interesting okay
16:04so I know that in this one I'm having
16:07difficulty with moving gases because of
16:10this decreased surface area available
16:12for gas
16:13exchange in interstitial lung disease or
16:16restrictive lung diseases for this
16:17matter what I know is if you have a
16:20problem where there's fibrosis of the
16:22Airways of the interstitial spaces I
16:24know that that's going to thicken the
16:26respiratory membrane and that's going to
16:27decrease diffusion capacity cuz if I
16:30increase the thickness I increase the
16:32denominator what will that do to the
16:33dlco it will also decrease the dlco so
16:37these both will decrease the
16:39dlco and I'm therefore I'm going to have
16:41a difficult time performing gas exchange
16:44or diffusion across this thick
16:46respiratory membrane or this decrease
16:48available surface area for
16:50exchange why this is helpful if I if I
16:53determine a patient has an obstructive
16:54lung disease off of the top two tests I
16:57do a Bronco dilator test and they showed
16:59that they more suggestive of COPD and
17:01then I want to determine is it osma or
17:03is it chronic bronchitis low dlco
17:05suggest osma rules out chronic
17:07bronchitis for the most part in a
17:09perfect world restrictive lung diseases
17:12I go through I determine they have based
17:14upon the top two test restrictive lung
17:15disease we don't really do Bronco
17:16dilator or Bronco constrictor test for
17:18them and then we do the dlco testing if
17:20it's low it tells me it's intrinsic lung
17:23diseases if it's normal it's suggestive
17:26of extrinsic lung diseases and that's
17:28super helpful so now what I want to do
17:30is I want to tell you guys step through
17:31step of how to diagnostically approach
17:34pfts let's do that now we check the F1
17:37over the FEC that's the ratio if it is
17:40less than 70% that means that it's an
17:42obstructive lung disease all right from
17:45there check the total lung capacity the
17:48residual volume the functional residual
17:50capacity and all of those it should be
17:52increased and their flow volume Loop
17:54would support that that it would shift
17:56to the left all right
17:59again that's suggestive of
18:02obstructive the next thing is to
18:04administer a Bronco dilator test because
18:05I want to know is it a patient who has
18:08asthma or
18:10COPD if I do that and there is a greater
18:13than 12% increase in their fv1 it tells
18:15me that they have a really significant
18:17reversibility of their disease so it
18:20suggests asthma I could then take it
18:22another step further and say okay it's
18:23reversible is it inducible give them
18:26methine if their f drops to greater than
18:2920% it definitely is suggestive of
18:32asthma in the other scenario if it's a
18:34less than 12% increase in the fv1 it
18:36suggests more of an irreversible process
18:38like COPD but which one is it is it osma
18:42or chronic bronchitis do the dlco if the
18:45dlco is going to be normal it's likely
18:48chronic bronchitis but if it's low in
18:49the scenarios of decreasing total
18:51surface area it's osma all right cool
18:55what if I said the F1 over the FC is
18:57greater than 7 % it's normal then okay
19:00but it could be suggestive of
19:01restrictive or normal how do I prove it
19:04check the TLC the residual volume and F
19:07FRC it would be normal in a normal
19:08patient but it would be low TLC RV and
19:11functional residual capacity and
19:13restrictive and the flow volume Loop
19:15would be shifted to the
19:17right that would be suggestive of
19:19restrictive okay how do I then go
19:20further and say restrictive lung
19:22diseases could be extrinsic or intrinsic
19:25check the dlco if I check the DLC o and
19:29there is a change in the lungs itself
19:31there's more thickening of the
19:33respiratory membrane it'll have a low
19:35dlco but if it has no change in that and
19:38it's normal DL so it's extrinsic if it's
19:41low it's intrinsic and it's an
19:43interstitial lung disease and that's how
19:45we would go about diagnosing obstructive
19:47versus restrictive lung disease based
19:49upon pfts all right my friends I hope
19:51that made sense I hope that you guys
19:52enjoyed it and as always until next
19:57time
19:58[Music]
20:04[Music]

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