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Respiratory system

Apnea and hypoventilation

Apnea of prematurity

Sleep apnea

Pleura and pleural space disorders


Pleural effusion





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USMLE® Step 1 questions

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A 61-year-old man comes to the clinic for a routine evaluation. He has had a chronic productive cough for the past 5 years, with occasional dyspnea and wheezing. He smoked a pack of cigarettes a day for 40 years, but stopped several months ago. Vitals are within normal limits. Physical examination reveals bilateral diffuse crackles and rales on chest auscultation. Pulmonary function testing (PFT) is performed, which confirms the diagnosis of chronic bronchitis-predominant chronic obstructive pulmonary disease. Which of the following PFT findings are most likely present in this patient?  

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α1 -antitrypsin deficiency p. 50, 401

emphysema p. 698

Centriacinar emphysema p. 698


emphysema p. 720

Elastase p. 382

activity in emphysema p. 698

Emphysema p. 698

α1 -antitrypsin deficiency p. 401

compliance in p. 689

diffusion in p. 690

diffusion-limited gas exchange p. 690

elastin in p. 50

panacinar p. 402

presentation p. 720


emphysema p. 720

Panacinar emphysema p. 402, 698


emphysema p. 698, 720


Emphysema means “inflate or swell”, which makes sense because in the lungs of people with emphysema, the alveolar air sacs, which are the thin walled air spaces at the ends of the airways where oxygen and carbon dioxide are exchanged, become damaged or destroyed.

The alveoli permanently enlarge and lose elasticity, and as a result, individuals with emphysema typically have difficulty with exhaling, which depends heavily on the ability of lungs to recoil like elastic bands.

Emphysema’s actually lumped under the umbrella of chronic obstructive pulmonary disease (or COPD), along with chronic bronchitis.

The two differ in that chronic bronchitis is defined by clinical features, like the productive cough, whereas emphysema is defined by structural changes, mainly enlargement of the air spaces.

That being said, they almost always coexist, probably because they share the same major cause—smoking.

With COPD, the airways become obstructed, the lungs don’t empty properly, and that leaves air trapped inside the lungs.

For that reason, the maximum amount of air people with COPD can breath out in a single breath, known as the FVC, or forced vital capacity, is lower.

This reduction is especially noticeable in the first second of air breathed out in a single breath, called FEV1—forced expiratory volume (in one second), which typically is reduced even more than the FVC.

A useful metric therefore is the FEV1 to FVC ratio, which, since the FEV1 goes down even more than FVC, causes the FEV1 to FVC ratio to go down as well.

Alright so say normally your FVC is 5 L, and your FEV1 is 4 L, your FEV1 to FVC ratio would end up being 80%.

Now, someone with COPD’s FVC might be 4 L instead, which is lower than normal, but the volume of air that he or she can expire in the first second is only 2 L, so not only are both these values lower, but their ratio is lower as well—and this is a hallmark of COPD.

All that had to do with air breathed out right? Conversely, for air going in, the TLC, or total lung capacity, which is the maximum volume of air that can be taken in or inspired into the lungs, is actually often often higher because of the air trapping.


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