Ep 174: A 65-Year-Old Man with Dyspnea on Exertion

From our Physiology at the Bedside series, this episode reviews pulmonary function tests.

Read more on this topic in Harrison's.

Harrison's Principles of Internal Medicine, 22nd Edition

Transcript

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[Ms. Heidhausen] This is Katerina Heidhausen, executive editor of Harrison's Principles of Internal Medicine. Harrison's Podclass is brought to you by McGraw Hill's AccessMedicine, the online medical resource that delivers the latest content from the best minds in medicine. And now, on to the episode. 

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[Dr. Handy] Hi, everyone. Welcome back to Harrison's Podclass. We're your co-hosts. I'm Dr. Cathy Handy. 

[Dr. Wiener] And I'm Dr. Charlie Wiener, and we're joining you from the Johns Hopkins School of Medicine. 

[Dr. Handy] Welcome to today's episode, a 65-year-old with dyspnea on exertion. 

[Dr. Wiener] Hi, Cathy. Today's our fourth Physiology at the Bedside episode, and it's one of my favorites. 

[Dr. Handy] I already have a guess, but let's go at it. 

[Dr. Wiener] So our patient today is a 65-year-old man who comes to you because he's had increasing dyspnea on exertion over the last six months. He used to easily beat his son in tennis, but now gets winded easily and is losing consistently. 

[Dr. Handy] I can see how that could either be inspiring or just depressing. Tell me more about his history. 

[Dr. Wiener] His past medical history is only notable for hyperlipidemia and being overweight for many, many years. However, he did smoke cigarettes until he was 55 years old and has about a 50-pack-year history of accumulation. His only medication is atorvastatin, and he works as a trust and wills attorney. He does not have paroxysmal nocturnal dyspnea, orthopnea, GE reflux, daytime hypersomnolence, or peripheral edema. 

[Dr. Handy] And his physical exam? 

[Dr. Wiener] So his BMI is elevated at 23, all his vital signs are normal, including his oxygen saturation of 97% on room air. His cardiac examination is normal. On lung examination, there are no bronchial breath sounds, wheezes, crackles, or rales, but expiration seems prolonged, and there are diminished breath sounds at the apices. His abdominal, neurologic, and skin examinations are all normal. 

[Dr. Handy] So he has an elevated BMI and some potential lung findings. Any more data? 

[Dr. Wiener] Yeah, his primary care physician ordered some basic labs, a chest radiograph, an echocardiogram, and pulmonary function tests. The labs were entirely normal. His chest radiographs showed no acute infiltrates and maybe some lung hyperinflation. The echocardiogram showed no left ventricular or valvular dysfunction with an estimated mean PA pressure of 30. 

[Dr. Handy] Okay, that PA pressure is slightly high. What about the PFTs? 

[Dr. Wiener] And that brings us to our question. 

[Dr. Handy] That was my guess, I first learned about PFTs from you in medical school, Charlie. 

[Dr. Wiener] Yep, and they're still useful so many years later. 

[Dr. Handy] So true. 

[Dr. Wiener] Okay, so the question says, which of the following statements regarding his PFTs is true? Option A. A reduced ratio of FEV1 to FVC suggests obesity. Option B. A reduced FEV1 to FVC ratio and reduced DLCO suggests emphysema. Option C. A reduced TLC suggests chronic bronchitis. Option D. An elevated TLC suggests interstitial lung disease. Or option E. An elevated DLCO suggests pulmonary hypertension. 

[Dr. Handy] Okay. Let's start at the basics. You mentioned the ratio of FEV1 to FVC, or the ratio of forced expiratory volume in the first second to the forced vital capacity. That represents the maximal expired volume. That calculation is derived from spirometry when you ask a patient to inspire to total lung capacity, or TLC, and then blow as much air out as possible by expiring to residual volume. The total amount of air expired under these conditions is the forced vital capacity. 

[Dr. Wiener] And how do you use that ratio of FEV1 to FVC? 

[Dr. Handy] Typically, that number is about 0.8, or you can expire 80% of your vital capacity in the first second. A reduction of that number, usually less than 0.7 or 70%, indicates an obstructive ventilatory defect. The classic diseases associated with obstructive ventilatory defects are COPD, asthma, or bronchiectasis. 

[Dr. Wiener] The question mentions both emphysema and chronic bronchitis. 

[Dr. Handy] COPD can manifest as prominent emphysema or chronic bronchitis, but most patients have a mixed phenotype. 

[Dr. Wiener] Tell me about TLC or total lung capacity. 

[Dr. Handy] Well, that requires measurement of lung volumes, usually by helium dilution. You can't get a TLC from spirometry because it can't measure the residual volume. A restrictive ventilatory defect is defined by a TLC less than 80% predicted based on height, age, and sex. 

[Dr. Wiener] What are the typical diseases that manifest with a restrictive defect? 

[Dr. Handy] Well, pathophysiologically, they can be broken down into intrinsic lung diseases and extrinsic lung diseases. Examples of intrinsic disease would be pulmonary fibrosis or sarcoidosis. The extrinsic causes include the chest wall disorders, such as severe obesity or kyphoscoliosis, or neuromuscular weakness, such as ALS or myasthenia gravis. All of those will cause a reduced TLC. 

[Dr. Wiener] And the DLCO? 

[Dr. Handy] The DLCO is the diffusing capacity for carbon monoxide, and that's an estimate of the patient's diffusing capacity for oxygen. It's a very sensitive measure with very little specificity. It is physiologically useful because when the DLCO gets below about 50% predicted, patients may develop symptomatic hypoxemia with exertion. Almost any lung disease that reduces either the surface area for gas exchange or the amount of blood in the lung can cause a reduced DLCO. 

[Dr. Wiener] Okay, that was a great refresher. So what's the answer to our question? 

[Dr. Handy] The correct answer is B. a reduced FEV1 to FVC ratio with a reduced DLCO is typical of emphysema. The low DLCO is because the emphysematous destruction of alveolar and capillary units will decrease the effective surface area for gas exchange. I suspect if we obtained a CT, we'd see bolus emphysema at his apices. And as I mentioned, if his DLCO is reduced, given his symptoms, his oxygen saturation during exercise should be checked. He may be hypoxemic during those tennis matches, which is causing his symptoms. Also, I mentioned before that almost all lung diseases will cause a reduced DLCO. Well, pure asthma or chronic bronchitis typically do not because they are purely airway diseases. 

[Dr. Wiener] Okay, great. Let's just run briefly through the other options on why they were incorrect. 

[Dr. Handy] Option A. mentioned obesity. Obesity will not cause a reduced FEV1 to FVC ratio. Mild to moderate obesity typically causes no ventilatory defects, but if anything, it will cause a reduced TLC and normal or high FEV1 to FVC ratio. 

[Dr. Wiener] Okay. Option C. mentioned chronic bronchitis, which you already told us has reduced FEV1 to FVC ratio and a normal DLCO. I assume that the TLC is not reduced. 

[Dr. Handy] Exactly. Chronic bronchitis alone should not cause a restrictive defect, but interstitial fibrosis will cause a restrictive defect and a reduced TLC. So that's why option D. is incorrect. 

[Dr. Wiener] Okay, the last option mentions pulmonary hypertension, and that was suggested on the patient's echocardiogram. 

[Dr. Handy] Yes, pulmonary hypertension of any cause, including emphysema, may cause a reduction, not an elevation, in the DLCO, and in the case of pulmonary arterial hypertension, that may be the only PFT abnormality. 

[Dr. Wiener] Okay. So in summary, today's physiology focused on pulmonary function tests, which include spirometry, lung volumes, and DLCO. They can help characterize an obstructive, restrictive, or gas exchange defect and help with your diagnosis and management of your patient. Emphysema will typically show an obstructive and a gas exchange defect. 

[Dr. Handy] You can find this question and other questions like it on Harrison's Self-Review, and you can learn more about this topic on the Harrison's chapter on the approach to the patient with diseases of the respiratory system. Visit the show notes for links to helpful resources, including related chapters and review questions from Harrison's, available exclusively on AccessMedicine. If you enjoyed this episode, please leave us a review, so we can reach more listeners just like you. Thanks so much for listening. 

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