Laboratory Diagnostics: Pulmonary Function Test (PFT)

by Carlo Raj, MD

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    00:03 We have been dealing with the laboratory techniques quite a bit. And what we are doing here is making sure that we know as to who is coming in and how to properly assess the information that’s going to come at you. At this point, you should be extremely adept at being able to delineate as to when test is used when and for what reason. So, on that note, let’s begin by looking at pulmonary function tests.

    00:28 Conventionally speaking, pulmonary function tests are used so that you can divide your obstructive versus restrictive lung diseases. With your pulmonary function tests and the type of graphs that we are going to create, you will see that you can get a heck of a lot more information out of it and what is expected of you at this junction in your medical education because of the evolution of the boards themselves. You will enjoy this because it’s building upon things that you already know.

    00:53 Now, the three main categories of the testing include the following. We’ll take a look at spirometry, of course, which is probably the most famous of them all. And with this, it’s the ratio of FEV1 over FEC that we will take a look at. What does it actually mean? It means the amount of air that you are able to get out in one second, forced expiratory volume, one second, over the total amount of air that you physiologically are able to get out which is only limited by, what volume please? Good. Residual volume. You cannot exhale your residual volume completely.

    01:32 Now, if it is obstruction, what does that even mean to you? It means that you cannot properly get your air out. You are obstructed. When that occurs, well, what kind of changes are we going to see? We will take a look. Must have a decrease in vital capacity and a decrease in total lung capacity for diagnosis of restriction. That is important and we will focus upon that. The obstructive part is quite simple. The obstructive means that, for the most part, I cannot significantly exhale. So, FEV1 is going to drop dramatically and you find that, well, for VC and TLC that for the most part, that will be a little bit different.

    02:15 In restrictive, both VC and TLC must be decreased in order for you to diagnose restrictive.

    02:21 You will see why. What kind of lung volumes become important for us, clinically? Total lung capacity and residual volume.

    02:30 As I told you earlier, there is no way that you can possibly measure residual volume.

    02:35 You must have a little bit of your air inside my lungs so that it does'nt collapse. Remember, it is always going to be at negative pressure. And that has to be kind of balanced by the fact that the chest wants to recoil, right? And so, therefore, that negative pressure has to remain and if you lose your air completely, well, that ends up being a problem and obviously, we will talk about that later. And blood or body plethysmography, in other words the "body box”, is really the gold standard for measuring the lung volumes. Plethysmography.

    03:09 The other tests that we will take a look at is the diffusion capacity for carbon monoxide, and we will call this DLCO. Now, please understand, carbon monoxide is used for different reasons in pathology. Carbon monoxide, here, clinically, will be used to see as to how quickly, this is by proxy, by proxy, you will utilize carbon monoxide to see as to how quickly it then diffuses across that membrane into pulmonary capillary. So, therefore, it is a good measurement of gas exchange. This does not mean you take a patient’s mouth and put it over a car exhaust. That is not very nice. Nor are you going to do that. This is just a little bit of carbon monoxide for diagnostic purposes. Now, if by chance there was a patient who got exposed to carbon monoxide from a car exhaust in a closed environment, granted garage, but more importantly, as to what occurs on a regular basis. We will talk about this later, especially during the winter, where there might be fumes and gases coming out of in the basement heater, what not. Or maybe those of you that enjoy the sport of hockey. And sometimes, you know, it gets cold in there and so, people that work in those ice rinks accidently leave their car on in a closed environment and anyhow, that is carbon monoxide poisoning. You see the difference now? This is only for diagnostic purposes.

    04:36 Both have heavy relevance for you and when the time is right, we will look at both.

    04:42 Let’s take a look at an overview of your lung volumes and capacities. I will only focus upon the ones that you need on this graph. Clinically, this is obviously from physiology. So, begin by looking at tidal volume. Right there in the middle there, looks like a waves that are really tiny and that’s your tidal volume. See labelled as such, at the end of the graph there. The tidal volume does not require any effort.

    05:07 It’s a fact that it’s quiet inspiration, quiet exhalation, that’s it. It’s approximately about 500, keep that in mind. As as we go through this, like we have been doing, there is going to be a lot of physiology involved only because we need to have this for clinical reasons. And then, well, that should go into breathing with inspired or great effort is then known as your inspiratory reserve volume. And once you go below your tidal volume with expiration, that is then known as your expiratory reserve volume. And so, some of these volumes that are important for us, however, include the following.

    05:48 Residual volume. That is the last bit of air that we have in the lung that you cannot properly void. There is no way that you can do that on spirometry, but some of those volumes that we talked about with the body box and such might help you figure out your residual volume.

    06:05 Next, the type of volume is the tidal volume, we looked at it. And then the capacities.

    06:09 The capacities that are important for us include vital capacity. Take a look at vital capacity, Includes everything except our residual volume. Vital capacity is important for us because it then explains forced vital capacity. That is part of our pulmonary function test. And it is not really timed in terms of exhalation. The other big capacity that we need to take a look at is function residual capacity.

    06:37 Functional residual capacity is more or less your control point. So, for example, when you have done your graphs. Your graphs, known as the-the graphs for inspiration-expiration, and the functional residual capacity be the control point, a ground zero in which, for example, if it is obstructed lung disease, then FRC is increased. If it is restrictive lung disease, FRC is decreased. We will talk more about that later. Total lung capacity is important for us. For example, here, a large lung, say that you see a huge lung on your AP diameter and also on your chest x-ray from anterior posterior, you find that there is a huge black areas of the lung where the diaphragm has then been pushed downward. That’s emphysema that I am referring to bilaterally. And there you can expect your total lung capacity to be increased. Okay, so those are some important volumes and capacitities that you want to keep in mind and that will be good enough for you to at least know what is going on clinically. Let's continue.

    07:44 Spirometry, what the patient doing? Takes a deep breath and then begins breathing out.

    07:48 That breath which is then coming out at one second is known as FEV1 and the forced vital capacity is the air that you are getting out without being timed. The ratio here of FEV1 over FEC ratio should be approximately 0.8. Now, if there is obstructive, what does that mean to you? Difficulty with getting air out, then you can only imagine which one of these parameters of the ratio has been affected severely. It’s your FEV1. Your FEV1, the amount of air that you are able to get at one second is severely obstructed. So therefore, you expect your ratio to decrease and that would give you something dramatically less than 0.8, 0.7. You are on the side of getting less, may be 0.3, 0.25. Without a doubt, your diagnosis, obstructive category. Your next step after you put yourself into obstructive category is to figure out which of the four. Is it emphysema? Is it chronic bronchitis? Is it bronchiectasis? Or is it asthma? And that part becomes fun.

    08:57 Restrictive. What does this mean? Well, let me put this out here. Please understand that with any type of lung disease, your FEC is going to be decreased. "But, Dr. Raj, you just said that the ratio is decreased with obstructive." Exactly, that is true. But your FEC is decreased, but who is decreased even more so? There you go. Your FEV1. That is the quantitative dramatic decrease that truly decreases the ratio. I don’t care what kind of lung disease, your FEC is always going to be decreased. Then what is it that determines the ratio? The FEV1. Do not get your vital capacity confused with functional residual capacity. Is that clear? Functional residual capacity is this, at control. Let me demonstrate. Well, actually I cannot, I will kill myself. I will sacrifice myself for medicine, but I am not ready to completely give myself up. But anyhow, point is, theoretically, FRC is your epiglottis open with absolutely no air moving in and out. I could try, but I think I would just look really bizarre. So, that is your theoretical FRC, ground zero. And do not get your FRC confused with FVC. And in any lung disease, FVC will be decreased.

    10:21 In obstructive, what is my FRC? Increased. Good. What about restrictive? What is my FRC? Decreased. I hope that is clear before moving on. If not, make sure you know your definition for some of these capacities that we have been talking about. Now, restriction is suggested by low FVC. Okay, fine. So, why is it that the ratio is either normal or perhaps even increased in restrictive? Because the FVC might be decreased, but FEV1 is definitely not as decreased as what we found in obstructive. So if that's the case, then please understand as that, well, you have a higher FEV1 number. You can actually have PFT, pulmonary function test, and its percentage being greater than 80%. So, I can say this to you factually that you will never, in restrictive lung disease, have a decreased ratio. I can tell you factually, that are both obstructive and restrictive will have a decrease in FEC. Is that clear? So, restriction is suggested by low FVC, but needs lung volumes testing to confirm because the residual volume is not measured by spirometry. So, confirmation comes from the fact that, well, you need to see as to whether or not residual volume or you tell me. Do you think residual volume is increased or decreased if we are dealing with restrictive? Give yourself one big example. A fibrosed lung. That is a lung that is absolutely non-compliant. It is very stiff. You can expect total lung capacity and you can expect your residual volume to be decreased in restrictive. Clear? For example, spirometry may show the findings of obstructive, but the decreased vital capacity.

    12:15 This could mean two possible clinical outcomes. What does that mean? For example, let’s do scenario A. CO, stop there, obstructive. What does this mean to you? You know that you have a severe decreased in FEV1. Your FEC is decreased, overall the ratio is decreased.

    12:34 You know that the TLC is increased and you know that your residual volume is increased.

    12:40 Now, COPD patient experiencing super imposed restrictive, stop there. Is that common? Yeah, it is. So, COPD experiencing superimposed restrictive disease, in which case the lung volume, the TLC, will also be decreased. Amazing, huh? So now, you have patient with spirometry that is now shown to have a decreased FEV1 to FEC ratio. But then all of a sudden, guess what? You need to further diagnose. Now that you start seeing your lung volumes and TLC being decreased, chances are pretty good that your patient with an obstructive disease had a superimposed restrictive. Fascinating, isn’t it? Exacerbations are always taking place. Do not forget that.

    13:24 What about scenario B? A COPD patient experiencing decreased VC. Okay, we know that. Due to hyperinflated lung trapping, without a superimposed restrictive condition. Therefore, what happens? Ah, confirmation by an increase in lung volume of TLC. So, priority number 1, confirm obstructive.

    13:50 You got yourself a decreased ratio. Fantastic! Well, you never know. There could be super imposement of restrictive disease, hence the lung volumes. In your particular case, may be you only need to go as far as obstructive. However, be careful, because you are going through answer choices and you do find restrictive disease, see to make sure that the lung volumes correlate with your initial diagnosis. Let’s take a look at a important pulmonary function test and loop spirometries that are relevant to your clinical understanding.

    14:24 Let’s take a look at the normal one first, right smack dab in the middle. Let's make sure, please, that we are absolutely confident about what the loops mean. What Y-axis, X-axis and the top and the bottom portion of the loop means. Let's begin. In the middle there, is normal. Next, well, what does that X-axis represent? Well for the most part, your volumes. I mean to say, well, how much is your lung filled with air? Let’s put it that way. You notice your residual volume and that will never change. You see the lines in blue, dashed line? That is residual volume, that is the air that is always going to be present normally in your lung, has to be.

    15:08 Next, well, as you move in the middle from 0, 2, 4, 6, please understand, that is, take a look at the end on your right, the X-axis is labelled as volume. Keep it simple. So as you move from right to left, from 0 to 6, that obviously means an increase in volume.

    15:28 Hmm, interesting! So, which one of these. which half of this loop represents inspiration? Please, please understand, it’s the bottom loop entirely. The entire bottom loop, from the beginning where it’s between 0 and 2 moved all the way up to 6, represents inspiration only. All of it. Stop. So now, you have ended at TLC, total lung capacity. That is full.

    16:01 Okay. Now, where do you gonna begin? Well, let’s go through some physiology. Where is my diaphragm? Oh, it’s passively moving up. Good. Passively moving up. Now, what happens? Oh, the alveolar pressure is becoming positive. What does that mean? It’s going to squeeze the air out through the alveolar ducts, moving it out. Good. What happens to your pleural pressure? The pleural pressure is becoming less negative, isn’t it? So, maybe it was at negative 8, now it’s moving down from negative 8 to negative 7, negative 6, negative 5 and then you have the recoil or elastic pressure, right? And that elastic pressure is becoming well, equivalent. Equivalent to your pleural pressure. It has to. So, this is the process of expiration that you should be oh so comfortable with before we move on to the exhalation aspect of this curve.

    16:59 There are three different things that are going on. There are three different pressures and please understand, at the end of expiration, we have now once again reached FRC technically.

    17:11 At the end of inspiration, we have now technically reached FRC. That means now the alveoli is filled. Where am I? At 6. You picturing this? Alveoli is filled with air and its pressure is pretty much equivalent. It’s at 0. FRC. The pleural pressure and the recoil pressure are both equal at approximately 8, shall we say. They are going to begin the process of expiration. Here comes the air out. The entire top loop, ladies and gentleman, represents expiration. You will divide this into the first half of expiration upon the top loop and the second half of expiration, exhalation. Now, during exhalation, the second half, wow, there isn’t as much air than coming out. Hmm, what does that mean? Think about that.

    18:05 As the air is coming out, then there is more pressure for it to close. So therefore, this is called dynamic airway expression. So that dynamic airway type of expression takes place usually the latter half of exhalation. This then brings us back to, well, where we started at? And you will notice here ladies and gentleman, that there is still little bit of volume left and that is your residual volume. This is a perfectly normal loop spirometry.

    18:33 Let's go to our first pathology. You will find that the pulmonary function test in FEV1 to FVC ratio is less than 0.7 or 0.8 and it’s at 0.3. This to you without a doubt means obstructive. No doubt, no doubt. What you need to confirm that it’s only COPD or that it’s only obstructive? The volumes, right? So, they will tell you that the volume, meaning the TLC is increased or they show you loop spirometry here. So, on your left is obstructive.

    19:06 How can you confirm that? Well, for two reasons.

    19:09 Number 1, the red loop represents the normal loop spirometry. What’s inspiration again? The bottom half of the loop. Inspiration has taken place, it is leaves you to 6. I told you with that type of pulmonary function test that you have a ratio that is less than 0.3 or its at 0.3. Then where is the air trapped? In your lung. Think of emphysema, that is your best one. Emphysema, the lungs are getting bigger, are they not? It’s a PA and AP everything shows increased diameter. There is going to be bilateral compression or depression of the diaphragm. And what about TLC? It was a 6. Oh look, it’s moved to the left. Now, it’s moved up to 8. No doubt now, that with the combination of ratio being decreased and TLC increased, confirmation of obstructive only without any super imposed restrictive.

    20:03 Is that clear? Next, I want you to begin the process of expiration. Expiration has taken place the first which is only the top half of the loop, the green curve, the top half and then you find that there is indentation. The scalp portion there represents, dynamic airway compression.

    20:22 Very quickly the airways, do they want to collapse. You got a problem. The air does not want to come out.

    20:28 Next, I want you to take a look at the residual volume. Is the residual volume in the normal? Take a look at the residual volume here. A lot more volume stuck in your lung.

    20:40 Obstructive, you can’t miss it. Now, let's go to the other side, shall we? Let me give you an example, pathological condition, there is a bunch with restrictive. These include interstitial lung disease which we shall categorise properly. When you think interstitial lung disease, you should be thinking about for whatever reason, there is fibrosis taking place in my interstitium. Clear? What else? Maybe pneumoconiosis. What are pneumoconiosis? Or maybe your patient was exposed to coal, asbestos, silica, berylliosis. My point is, there is a bunch of differentials for restrictive. At this point, you find that the FEV1 to FVC ratio is normal at 80%. Interesting! But yet your patient was exposed to coal? Wow! And I find that the chest x-ray that it’s a reticular pattern with mesh work. Okay.

    21:35 So, now, what are you thinking? Maybe, most likely, restrictive. Once again, the normal would be the red loop. Now, you have a very fibrosed lung and we will talk about this as being a worst case scenario, progressive, massive fibrosis with a very non-compliant lung which is stiff. Please understand that you don’t have any problem getting here in, but you only get a little bit of air in. How can you confirm that? Take a look. You only moved up to approximately, well, little bit less than 4, may be only up to 3 litres. Normal is up to 6. So, tell me about your TLC. The original TLC was 6, it has now moved down to approximately 3. No doubt, your FEV1 to FVC ratio being normal only suggestive and with that history and the lung volume and TLC being decreased, has to be restrictive.

    22:29 Are you seeing this? Let's continue.

    22:33 Other important patterns that you want to keep in mind. You will like this. Watch. The first one is called fixed obstruction. What does this mean? Well, this could mean that first and foremost, let’s begin the same way, organisation.

    22:50 The loop spirometry, different pathologic patterns that you are responsible for understanding.

    22:54 We will begin with residual volume. Okay. Does this-Does this even look normal? No, it doesn’t. Actually, the both, the bottom half and the top half look like they are kind of sandwiched, isn’t it? It looks like a-a burger, doesn’t it? Looks like buns. That’s what it looks like. And that black line in the middle, that is your piece of bacon. I don’t know, whatever. So, the point is they are compressed. What happened here? There is difficulty with inspiration, hence flattened and there is also difficulty with expiration. What the heck kind of disease is going to give you a fixed obstruction? A ENT tumour. In other words, you have perhaps dangerous, a head and neck type of cancer. When there is a head and neck type of tumour, cancer, this is then causing a fixed large obstruction of both inspiration which is the bottom half of the curve and the top half.

    23:48 That is fixed. Let's move on to another one.

    23:52 Now, first and foremost, dissect the curve, interpret this. Where is my problem, please? Inspiration? Exhalation? Good. Inspiration only. You see that there is only a problem with inspiration. Wow! What the heck kind of problem or disease of pathology has given me a problem with inspiration only? The problem is extra thoracic pathology. Meaning, maybe with the vocal cords. So, with the vocal cord type of dysfunction or maybe perhaps fibrosis or an upper airway mass, this is the most tested, well, please understand, that you are going to have a hard time inspiring. Is that clear? So, therefore, the bottom half of the curve has not been affected. But, you do not have problems at getting the air out.

    24:41 This is not, I repeat, anything to do with obstructive in terms of the pulmonary issue. Obstructive here, I wouldn’t even use this word. I would just think of this as being inspiratory issues.

    24:55 Now, we do think about obstructive. I want you to keep the theme of obstructive and inside the lung. First and foremost, interpret the curve for me. Where is my problem? Good. The top half. What does that top half represent? Exhalation. Interesting! Earlier discussion, I just showed you obstructive lung disease with scalloped type of second half of exhalation with a left shift, meaning to say, an increase in TLC. That was obstructive. Here, please understand, when you have such a obstructive pattern, that you will see at some point in time, that this is a problem inside my lung and this will be something like obstructive disease, or but also, intrathoracic tumour whereas the tumour in the first one, fixed.

    25:48 Where was it? Oh, ENT. Ear, Nose, Throat. Clear? Blocking, fixed. What was the one with extrathoracic? That was vocal cord, problem with inspiration only. More common than you think, especially in health care workers. Vocal cords often times, often times damaged.

    26:07 Now, under the three main categories, take a look at lung volumes. TLC, residual volume, and once again, the Gold standard here for measuring lung volume will be a body box, plethysmography. Lung volumes used in measuring residual volume, we talked about that spirometry cannot, report’s out, your TLC and vital capacity will be two big ones. Then reduced TLC seen in what kind of disease, please? Good. Restrictive. Elevated TLC and residual volume will be seen in what kind of disease, please? Good. Obstructive. We will call this hyperinflation.

    26:45 Our third and final category, extremely important, diffusion capacity carbon monoxide. What does this mean? As I said, you are not taking your patient and putting them on a car exhaust.

    26:57 No, be kind. You are going to give just enough carbon monoxide in which you are then going to measure for how quickly, does my oxygen, by proxy move into my capillary.

    27:08 Why don't we just use oxygen? Because it’s so slow. Okay? Carbon monoxide, boom.

    27:13 It’s like 20 times quicker to diffuse across. Not to mention, carbon monoxide is highly, highly and has great affinity to haemoglobin, doesn’t it? So, all these things make it very, very important to use carbon monoxide and to test your diffusion.

    27:31 Now, what does that even mean? Be careful here because this is how you interpret it.

    27:35 That is all fine and dandy. You got the facts down, but what does it actually mean in terms of test? If your DLCO is decreased, meaning that the ability for this oxygen to diffuse across your membrane has been compromised, your DLCO will be decreased. Clear? For example, say that you have increased barrier between the alveoli and into the pulmonary capillary.

    28:01 An increased barrier. Give me a pathology, in general. Good. Fibrosis. What if you have left-sided heart failure? What is the barrier now? Oh, it’s fluid. What do we call this? Pulmonary edema. Now, if you have such a barrier, first and foremost, tell me about that A-aO2 gradient that we talked about earlier. Air is stuck in my alveoli, the diffusion goes down, my little “a” is going to further decrease. You can’t properly diffuse. A-aO2 gradient, widened. Now, next, I just gave away the magic statement. Increased thickness, decreased diffusion, you expect your DLCO to decrease. Clear? That is your best example there. Let’s take a look.

    28:53 It can be reduced because of surface area. Who is? DLCO is, diffusion capacity carbon monoxide. Why? In emphysema, I thought, I thought, I thought, hold on. You might have thought that it was increased compliance and therefore, makes it easier. No.

    29:10 Granted, emphysema is a very compliant lung. It wants to expand like crazy, but how much damaged you have your parenchyma? Quite a bit, huh? So, what happens to the surface area? Decreases. So, when you lose surface area, can you have proper gas exchange? Of course, not. That’s why you have COPD. That’s why you have a decreased DLCO. Let’s continue.

    29:32 When else could it be decreased? Oh, there it is. Greater barrier to diffusion including fibrosis or maybe pulmonary edema. But, there is one big exception that I need to give you.

    29:45 Let's just say, I will just put it out there for now. The one big exception will be alveolar haemorrhage. Is that clear? You will see why. Next, sometimes increased in asthma. So, what does that mean, when it increases? It means that the oxygen is travelling across that membrane very quickly. Early on in asthma, what could the patient be doing? Breathing a little bit faster because of asthma and if there is proper gas exchange, they might actually increase the gradient. And therefore, oxygen might get across as the membrane very quickly. There might be an increase in DLCO or to asthma, keep that in mind, please, when you are reading a stem of any type of clinical vignette.

    About the Lecture

    The lecture Laboratory Diagnostics: Pulmonary Function Test (PFT) by Carlo Raj, MD is from the course Pulmonary Diagnostics. It contains the following chapters:

    • Pulmonary Function Testing
    • Spirometry
    • Loop Spirometries
    • Other Spirometry Patterns
    • Diffusion Capacity

    Included Quiz Questions

    1. FEV1/FVC
    2. TLC and RC
    3. Diffusion capacity of CO
    4. VC and TLC
    5. FEV1/TLC
    1. It cannot be expelled because prevents the lungs from collapsing
    2. It is the amount of air that is fully diluted by N2 or He
    3. It is responsible for the recoil of the chest wall
    4. It represents limitations on airflow
    5. It represents the surface area available for gas exchange
    1. Body plethysmography
    2. Spirometry
    3. DLCO
    4. FEV1/FVC
    5. Gas dilution
    1. Inspiratory capacity + expiratory reserve volume
    2. Inspiratory capacity + tidal volume
    3. Inspiratory reserve volume + tidal volume
    4. Inspiratory reserve volume + expiratory reserve volume
    5. Tidal volume + expiratory reserve volume
    1. Expiratory reserve volume + residual volume
    2. Expiratory reserve volume + tidal volume
    3. Tidal volume + residual volume
    4. Vital capacity + residual volume
    5. Expiratory reserve volume + inspiratory capacity
    1. Increased TLC
    2. Decreased residual volume
    3. Increased tidal volume
    4. Decreased functional residual capacity
    5. Decreased total lung capacity
    1. Obstructive lung disease
    2. Restrictive lung disease
    3. Decreased residual volume
    4. Increased tidal volume
    5. Increased FEV1
    1. Restrictive lung disease
    2. Obstructive lung disease
    3. FEV1/FVC ration < 0.8
    4. Increased TLC
    5. Drastic decrease in FEV1
    1. Obstructive lung disease with superimposed restrictive lung disease
    2. Improvement in the obstructive lung disease toward a normal FEV1/FVC ratio
    3. Obstructive lung disease that has progressed to restrictive lung disease
    4. Increased forced vital capacity
    5. Increased vital capacity
    1. Residual volume
    2. FEV1
    3. FVC
    4. FEV1/FVC ratio
    5. Expiratory reserve volume + tidal volume + inspiratory capacity
    1. Inspiration
    2. Expiration
    3. Residual volume
    4. Obstruction
    5. Restriction
    1. The end of exhalation marks the maximum TLC
    2. Pleural pressure becomes less negative
    3. Elastic recoil pressure approaches equilibrium with pleural pressure
    4. Diaphragm passively moves into thoracic cavity
    5. Alveolar pressure becomes positive
    1. Residual volume has increased
    2. TLC has decreased
    3. FEV1 has increased
    4. FRC has decreased
    5. Expiratory capacity has increased
    1. Shift in the loop to the right
    2. Normal loop spirometry
    3. Shift in the loop to the left
    4. Increased residual volume
    5. Increased TLC
    1. Fixed obstruction
    2. Variable intrathoracic
    3. Variable extrathoracic
    4. Obstructive
    5. Restrictive
    1. Variable extrathoracic
    2. Variable intrathoracic
    3. Obstructive
    4. Fixed obstructive
    5. Restrictive
    1. It represents an exhalation dysfunction
    2. It represents an inhalation dysfunction
    3. It shows a decrease in residual volume
    4. It shows a decrease in TLC
    5. It represents a mixed obstructive and restrictive pattern
    1. It diffuses across the alveolar membrane faster than O2
    2. It binds to hemoglobin with a lower affinity than O2
    3. It can be tagged using radioactive markers
    4. It is a significantly smaller molecule
    5. It has a higher partial pressure in room air
    1. Widened A-a gradient
    2. Increase in alveolar surface area
    3. Decreased alveolar blood flow
    4. Decreased thickness of the alveolar membrane
    5. Increased diffusion of non-oxygen substances
    1. There is a greater barrier to diffusion at the level of the alveoli
    2. There is a greater barrier to diffusion at the level of the bronchi
    3. There is an increase in surface area
    4. There is a decrease in oxygen saturation
    5. There is an increase in residual volume

    Author of lecture Laboratory Diagnostics: Pulmonary Function Test (PFT)

     Carlo Raj, MD

    Carlo Raj, MD

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