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Snapshot Series on Respiratory Medicine



The on-demand teaching session is an in-depth exploration of spirometry and other pulmonary function tests. It explains how these tests provide invaluable insight into a variety of respiratory disease processes by assessing lung volumes over a specific time period. Using illustrative graphs, it describes how these are interpreted to aid clinical decisions. The session also provides specific examples of obstructive and restrictive lung diseases. It explains how spirometry can identify such diseases, monitor their severity, and ultimately guide treatment plans. It concludes with a case study of a patient depicting these concepts in a practical scenario. This video is a comprehensive guide, beneficial for any medical professional looking to enhance their understanding of pulmonary function tests and spirometry and apply this knowledge to their clinical practice.
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This is the first in the second part of the snapshots in respiratory medicine series. This video will cover spirometry as a pulmonary function test and why it is a useful investigation to utilise. It will also incorporate a few case studies to help us integrate the history and examination with our investigations to help further refine our clinical reasoning.

Learning objectives

1. To understand the purpose of pulmonary function tests and how they can add value to a history and physical examination. 2. To identify different types of pulmonary function tests and how each one contributes to diagnosis of respiratory diseases. 3. To gain an in-depth understanding of how spirometry works, including an understanding of how to read and interpret spirometry results. 4. To differentiate between obstructive and restrictive pulmonary disease patterns on spirometry. 5. To apply the knowledge of pulmonary function tests and spirometry in evaluating a clinical case, such as diagnosing and monitoring the severity of a respiratory disease.
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Computer generated transcript

The following transcript was generated automatically from the content and has not been checked or corrected manually.

Hello and welcome back to the Snap series in Respiration Medicine um SED and we're continuing our series with a video on spirometry. And in a broader overview, look at pulmonary function tests. Just as a side note, our series is still available for all previous videos on metal. The links will be posted through the phase one and phase two bulletin on our Instagram and on our Facebook. So let's get started. These are some of the key objectives I wanna consider in our video today. So what is the purpose behind pulmonary function tests? So why do we use them? How can they add a value to our history and examination? What are the different types of tests we have available to us? And then more specifically about how the spirometry work and a flow diagram on how we can interpret spirometry to help us make clinical decisions. So why do we use pulmonary function tests? These are a few reasons why we use them, but there may be more but primarily the reasons that came to my mind were number one, they can help you in defining patients and understanding the underlying disease process in a patient who is symptomatic or respiratory disease. For example, there may be a specific pattern of abnormalities associated with different disease processes. Ie there may be a restrictive pattern versus an obstructive pattern and that may then lead patients on or may lead the clinician onto an uh further diagnosis. For example, patient with cough who has mucopurulent sputum, who then has an obstructive pattern. You might be considering bronchiectasis for example. And finally, they can be used for disease severity. For example, fev one is a good example where it can be used in COPD to look at the severity of their disease process. So pulmonary function test can also be used to regularly monitor and quantify the severity of a person's disease. The different tests available vary. But the most standard tests generally include spirometry, which we'll discuss further peak flow meters, which are devices which can be used to look at their maximal expiratory flow and is typically used in asthma quite classically. And the DLCO which is a test that looks at the diffusion of carbon monoxide across the alveolar membrane. And it provides a measure for gasses exchange um on and how easily um oxygen and carbon dioxide can traverse the alveolar cole membrane to ultimately then oxygenate the blood. The AVG isn't a conventional pulmonary function test, but it can be used to assess acid base status, which can be important as the lungs are very important in acid base regulation, especially in the early phases where the kidneys play a more important role in terms of long term acid base regulation. So this is a cartoon representation of spirometry. And in this image, we can see that the person has nose clips and their mouth is sealed around a mouthpiece through which they're gonna inhale and exhale. And it's the flow of air through this mouthpiece, which is then recorded by the spirometer to then measure a person's lung volumes over a specific time period. This is a graph depicting the, the typical picture you'd see from a spirometer. It's very classical. You've probably seen it when you're learning about spirometry and physiology. And this is simply a recap. Tidal volume is as we all know, the volume of air that passes in and out of the lungs are in normal inspiration and expiration when you're at rest with the aspiration and expiratory reserve volume, with the extra volume of air that you can breathe in or breathe out above the normal. Typically, when using accessory muscles of respiration with the residual volume being the portion of air that remains in the lungs. After maximal expiration, there is always a small amount of air present. The lungs are never fully collapsed. The functional residual capacity is the volume of air that's left in the lungs after normal expiration at rest. And the inspiratory capacity is the combination of the tidal volume plus the inspiratory reserve volume. So the amount of air you can maximally inspire two values are very specific and very important for spirometry interpretation and we've probably come across them before. And this is the FVC, which is a forced to capacity ie the volume of air that can be maximally expired in a period of six seconds after a maximum inspiration. With an FEV one being the volume of air that can be maximally expelled within one second of their maximum aspiration. And it's the ratio between the two that provides a very useful value. When you're looking at spirometry interpretation, there's two main patterns on spirometry to consider that's an obstructive lung disease pattern versus a restrictive lung disease pattern. In obstructive lung disease. The issue is in expiration with restrictive lung disease. The lungs are have less compliance, they're harder to expand. So you have an issue with inspiration and that has a proportional knock on effect in expiration in obstructive lung disease. The classical picture is an FEV one to an FVC ratio which is reduced and this is because the FEV one is gonna be reduced and impacted more early in the force V capacity. So you may have individuals that have a normal FBC but have reduced FEV one to FBC ratio of less than 70%. And examples of obstructive disease processes include asthma as a reversible area of obstructive disease, irreversible, including COPD bronchiectasis and cystic fibrosis. With examples of restrictive lung disease to consider being the broad spectrum of interstitial lung diseases. You can also consider patients with neuromuscular disease processes like myasthenia gravis. Patients with obesity or patients with musculoskeletal issues like scoliosis. Pulmonary vascular disease. Being this tertiary group of disease processes like pulmonary hypertension or patients who maybe have repeated um pulmonary emboli where you have damage to the alveolar capillary membrane, specifically on the vascular aspect. And they would present typically with normal lung mechanics, ie normal fev one to F PC ratio. They would have normal FVC, normal FEV one, no reduction. The only way you can really pick it up is with abnormal D OC O values because of damage to the vascular membrane. There is issues with gas exchange at the capillary membrane and this therefore is to decrease D OC O. So there is there is reduced ability for for substances to cross that um diffusion pathway. And that's why do two is very important as a pulmonary function test to help you distinguish between normal lung mechanics and somebody with potential underlying pulmonary vascular disease. This is an example of a flow volume diagram and it's a loop. And you can see that this is expiration and this is inspiration and this is the normal lung mechanics. At this point. Here, you have the peak expiratory flow rate because this is the maximal flow and expiration at that point on the graft. And you can see with the restrictive lung disease, there's a proportion of reduction in all parameters, but the actual shape of the curve is very similar to the normal and that's classical for restrictive lung disease where all values are reduced. And ultimately, this is because the lungs are less compliant, less able to expand. And as such, you have a reduction in the inspiratory volume. And in a proportion of reduction in the expiratory volume, the obstructive pattern to consider really the obstructive pattern to really consider would be that you can see this classical notching, which is known as a curving, curving sign or curving notching in expiration with normal or or practically normal inspiration. And this coving is because of the resistance of the airway, which is primarily in expiration and this causes issues. You can see that your peak expiratory flow rate is reduced much like it is reduced in restrictive lung disease. And ultimately, this is the shape of the curve which is a sign of obstructive lung disease. These are the curves are more variable, providing signs of upper airway obstruction or extrathoracic airway obstruction. So this is a volume time plot. Ultimately, you can see that there is a distinction made with the obstructive versus restrictive lung disease in mild obstructive lung disease due to the issue in expiration and the resistance of the airway in expiration, which obstructs the expiratory airflow, it takes them longer to expel the same amount of volume of air, but they do expel the same amount of air. And you can show that this is proven by the less steep curve. So it essentially takes them less time. And the grading of this curve is actually a measure of the expiratory flow rate. With the steepest point being the point where you have the peak expiratory flow rate. Restrictive lung disease is very diff different in restrictive lung disease. Because of the issues in expanding the lungs, you therefore have a reduction in the inspiratory volume and ultimately a proportional reduction in the expiratory volume. So therefore, your FDS could be reduced early on. But the F EV one to F PC ratio itself would remain fairly similar. You can see that because here you can see the steepness of the curve is fairly similar. It is just that because of the reduction in the F PC, the F EV one is also proportionately going to be reduced because they have less air to expel in that one second because they've inhaled less air. Hopefully, that hasn't been too confusing. If you have any questions, please email me about this. And this is a flow diagram which ultimately I use, which helps me interpret spirometry and hopefully it is useful for you guys. So the first thing I would do is to look at the F one to F PC ratio, is it reduced? Yes or no, if it is reduced, this is a sign of potential obstructive lung disease. You have to look at the F PC if the FBC is normal, this suggests potentially mild obstructive lung disease. But if the FBC is low, this could be severe obstructive lung disease, which is impacting on the force by capacity. Or it could simply be a mixture of obstructive and restrictive lung disease because patients are heterogenous and they can have a combination of disease processes going on. If the F one to F PC ratio is not reduced and it's either normal or increased, you need to still look at the F PC. If the F PC is normal or high, this suggests either what two things, they have normal lung mechanics and they are perfectly healthy or they could have potential pulmonary vascular disease, which you can only identify or which which one investigation we at our stage, we can identify is using the D OC O which may be decreased. We would look at the FBC if the F EC is low and the F one to F PC ratio is no more or high. This suggests restrictive lung disease processes generally. So that's the end of the sort of didactic section of our, of our presentation. We're gonna move on to a few cases now. So whenever you feel ready, pause the video, have a go and then come back to, to view the answers. So in this case, we have a 65 year old male with a chronic history of shortness of breath exacerbated by triggers like the cold and running, which is classical for somebody with potential asthma. They have a history of chronic cough and their post bronchodilator if, if you want a PC ratio shows an improvement of more than 13%. Suggesting that this is a reversible airway obstruction. You look at the F one to F PC ratio, you can see it's really low at 0.28%. Now, this is extreme, extremely low, but it's the same, just a obvious example. So the F EV one to F PC ratio is less than 70%. They've got this reversibility with bronchodilator therapy and they've got chronic cough. So the diagnosis is reversible obstructive lung disease, consistent with the diagnosis of asthma. So the answer to question one. So this is case two, once again, feel free to pause the video and have a go. And in this case, we have a 35 year old male with a three month history of shortness of breath, which is persistent and constant. Now, it's important to look at the history and specifically in respiratory history. It's very important to have a good family history, drug history, but also occupational history and social history, especially for any pets. And he owns some pet parakeets. When you look at his spirometry results, there was no improvement with bronchodilator therapy. And when you see the F if you want to F PC ratio, you can see that it is normal or it's increased above the normal of 70%. And you can also see that their total lung capacity and their residual volume is also reduced. Suggesting that they've got reduced uh entry as well or they've got reduced lung volumes. In general, the D OC O is also reduced, suggesting difficulty in gasses exchange at the alveolar membrane. All of this comes together to suggest that this patient may have restrictive lung disease, consistent with a diagnosis of hypersensitivity, pneumonitis, its hypersensitivity, pneumonitis secondary to the pet parakeets. The D OC O shows that it's an issue with diffusion and gas exchange. And it's important to know that interstitial lung diseases which have fibrosis and their position of of thick fibrotic tissue within the interstit impacts and thickens the diffusion pathway, therefore making it harder for acid exchange to occur. Finally, this is case three, our last question once again, have a go pause the video and then come back for the answer. So in case three, we have a 42 year old lady presenting with a history of dyspnea. Ultimately, the key aspect here is to understand and interpret the flow diagram. So this is a volume time plot. You can see the FBC is reduced and the FEV one is reduced. And this is characteristic of a restrictive pattern. Whereas with an obstructive lung disease pattern on the volume time plot, it would take you a longer time. But ultimately, they would be able to expire maximally to the FB with restrictive lung disease because of the reduced ability to actually expand the lungs and inhale enough air. You have a proportional reduction in the amount of air you can expire as well. And this is reflected here with the reduction in the inspiratory volume. And then the proportionate reduction in the expiratory volume and the proportion of reduction in the peak expiratory flow rate where ultimately restrictive lung disease has a pattern on the flow volume plot which is essentially identical or very similar to the pattern of the normal expiratory inspiratory flow volume diagram um in all proportions except that it is slightly smaller. Hopefully, this presentation has been useful in helping you understand a bit more about spirometry. If you have any questions, please feel free to email me. My email is um AAA 138 at student.ae.ac.uk. Thanks for listening and look out for this video and also other future videos and past videos on meal. Have a nice day.