15-year-old (male) with shortness of breath

by Mohammad Hajighasemi-Ossareh, MD, MBA

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    00:02 A 15 year old boy visits the clinic with his mother as he is having some breathing difficulties for the past few months.

    00:09 He is very interested in sports and wants to join the school basketball team.

    00:13 When he signed up for after-school training sessions, he found that he was getting short of breath after 15-20 minutes.

    00:20 He does not experience this symptom at any other time.

    00:23 He is a healthy child and up to date with all of his vaccinations.

    00:27 There is no family history of respiratory diseases.

    00:30 His vitals are respiratory rate 14, pulse 87, blood pressure 110/89 and his temperature is 36.7 degrees celsius.

    00:39 His physical examination is normal including a normal respiratory examination.

    00:44 He is advised to take a pulmonary function test during which he is asked to take in as much air as he can and then forcefully expire all the air into a spirometer.

    00:54 The volume of expired air represents which of the following? Answer choice (A) - Expiratory reserve volume Answer choice (B) - Functional residual capacity Answer choice (C) - Tidal volume Answer choice (D) - Total lung capacity Answer choice (E) - Vital capacity Now take a moment to go through the answer choices by yourself before we go through them together.

    01:25 Okay let's jump right into this question.

    01:27 Let's tackle the question characteristics.

    01:29 Now this is a physiology question.

    01:31 It expects us to know what the lung is doing and how that corresponds to certain categorization in pulmonary function test.

    01:39 Now this is a 2-step question.

    01:40 We have to think, 'Okay, what are the parameteres that are measured by spirometry and then what's described in the question stem correlates to which component of spirometry measurement? And thus the stem is absolutely required as we have to understand the clinical situation in which we're performing spirometry, and also be able to know what questions being asked with the maneuver being performed.

    02:01 Now let's walk through this question.

    02:03 Well, step 1 - first we have to consider the parameters that are measured by spirometry.

    02:07 Now, a spirometer measures the volume of air inspired and expired by the lungs.

    02:14 Now the variables that are seen with spirometry include FEV1, vital capacity, tidal volume, inspiratory and expiratory reserve volumes which can all be measured by spirometry.

    02:25 Now let's refer to our image of what we can see there as different variables included in a spirometry measurement.

    02:32 Now looking first at the middle, we see the inspiratory going upward and the expiratory going downward between 30 and 37 ml/kg And that correlates to as our tidal volume.

    02:42 That's how much someone will breathe when they're breathing normally at rest.

    02:46 Now, if we look upward into what's called the inspiratory reserve volume or IRV that's when someone takes a breath in after normal inhalation and holds it there, that's what's called inspiratory reserve volume.

    03:00 That means, and a very common way to think about it is, when you're breathing normally and then I ask you to take a big breath, what was your inspiratory reserve? and that's what it is - inspiratory reserve volume.

    03:11 And below we'll see the same thing, something called expiratory reserve volume, meaning that, when you are breathing normally and then I ask you to give me a big exhale, how much expiration reserve did you have? So that's expiratory reserve volume.

    03:24 That makes a lot of sense.

    03:26 Now we have something next to look at below called residual volume.

    03:30 That means after I've asked you to blow all the air you can, how much air is left in the lungs? And that's residual volume.

    03:37 Now you can't blow out all the air in your lungs because there are some amounts of air that is needed to keep the alveoli open and that is always going to be in the respiratory circuit.

    03:45 And that is your residual volume.

    03:47 Now, the next two we see are the inspiratory capacity and the functional residual capacity.

    03:54 Now, inspiratory capacity means after I've asked you to take a breath in after your exhale, that's your inspiratory capacity.

    04:04 Now you may ask yourself, how is that different than inspiratory reserve volume? Well, inspiratory reserve volume actually starts with your normal inhale.

    04:14 So you're taking all breath in, then you take the rest of your inhalation and that's how much inspiratory reserve you have left.

    04:21 But inspiratory capacity starts measurement after your normal exhale.

    04:26 That is, after you normally exhale and then you take a big inhale, that's how much inspiratory capacity you have.

    04:32 Then you have what's called functional residual capacity which means, after you've given me a normal exhale, go ahead and give me your full exhale again.

    04:43 Now, this includes residual volume.

    04:46 So functional residual capacity can actually be measured mathematically by taking the expiratory reserve volume and adding on the residual volume to come to that measurement.

    04:56 Now, the next measurement is vital capacity.

    04:59 Now if I ask you to take the biggest breath you can in and let it all the way out, that's the vital capacity we call or the amount of air your lungs can handle on your full inspiration and your full expiration which is what this person did in the clinical question stem.

    05:15 And the last variable to consider is what's called total lung capacity which is all the air that you could expire and inspire for the vital capacity plus the residual volume and that's all the air that your lungs can hold.

    05:29 Now, then looking back at the question stem, this person was asked to take in as much air as he could and then forcibly expire all the air into the spirometry which then correlates into what's called vital capacity or answer choice (E) in this case.

    05:44 Now, looking at that, let's go back to understanding why he got vital capacity.

    05:50 So the maximum amount of air that can be forcefully expired after a deepest possible inspiration is called vital capacity, so that's what they described in the question stem and we can see in the image is what happens to this patient.

    06:03 Now vital capacity, look at your image to understand, is the sum of the inspiratory reserve volume, tidal volume and expiratory reserve volume.

    06:11 Now, total lung capacity though is vital capacity plus the residual volume.

    06:16 And remember that residual volume is the volume of air that is left in the lungs after maximum forceful expiration that cannot be measured by spirometry.

    06:25 Now let's review some high-yield facts regarding spirometry.

    06:29 Okay, spirometry measures volumes of air inspired and expired by the lungs.

    06:34 Spirometry can measure FEV1, vital capacity, tidal volume, inspiratory and expiratory reserve volumes.

    06:40 Spirometry cannot however measure residual volume, which is the volume of the air left in the lungs after maximal forceful expiration.

    06:48 And total lung capacity is vital capacity plus the residual volume.

    About the Lecture

    The lecture 15-year-old (male) with shortness of breath by Mohammad Hajighasemi-Ossareh, MD, MBA is from the course Qbank Walkthrough USMLE Step 1 Tutorials.

    Author of lecture 15-year-old (male) with shortness of breath

     Mohammad Hajighasemi-Ossareh, MD, MBA

    Mohammad Hajighasemi-Ossareh, MD, MBA

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