Q&A Medicine>>>>>Pulmonology
Question 11#

A 62-year-old man presents to the clinic with dyspnea on exertion. He reports a progressive decline in his exercise tolerance over the last few years, and complains that he feels like he is always coughing up white mucus. He denies any fever, weight loss, hemoptysis, chest pain, or leg swelling. His medical history is significant for hyperlipidemia and GERD, for which he takes atorvastatin and omeprazole. He has smoked a pack of cigarettes daily for the past 40 years. He is afebrile with normal vitals. On examination, he has decreased breath sounds with a prolonged expiratory phase and scattered wheezes. There is hyper-resonance to percussion in bilateral lung fields. The rest of the examination is unremarkable, and he is referred for further testing with spirometry.

Which of the following represents the likely flow–volume loop in this patient (Figure below)? 

A. Option A
B. Option B
C. Option C
D. Option D

Correct Answer is B

Comment:

Option B. COPD is a common condition resulting from chronic inflammation of the airways leading to progressive airflow limitation. Most cases occur in older patients and are the result of chronic smoking; in a young patient without a significant smoking history, consider other causes (such as α1-antitrypsin deficiency). There are two processes that typically occur in COPD: emphysema (a histopathologic finding) and chronic bronchitis (a clinical finding). The type of emphysema seen on histology is centrilobular, whereas in α1-antitrypsin deficiency it is panacinar. Emphysema is the result of parenchymal destruction from chronic inflammation, which creates enlarged airspaces. With the loss of the supporting connective tissue, the lungs lose their elastic recoil and the airspaces enlarge, creating high lung volumes; in addition, small airways collapse during expiration due to a loss of tethering that the connective tissue provides, which causes air trapping and further expansion in lung volumes. This affects respiratory function by decreasing both ventilation and perfusion via destruction of airspaces and vasculature, leading to mild hypoxemia.

Chronic bronchitis is defined as having a productive cough for more than 3 months of the year for at least 2 years. Inflammation of small airways causes narrowing and excessive sputum production leading to increased airway resistance and a prolonged expiratory phase. This causes V/Q mismatch and hypoxemia. The end result of both emphysema and chronic bronchitis is high lung volumes with increased compliance (large changes in volume based on small changes in pressure, the opposite of elasticity), leading to increased dead space during ventilation and chronic hypoxemia.

This patient presents with classic symptoms of dyspnea on exertion and chronic productive cough, with physical findings highly suggestive of COPD. Spirometry is required to make the diagnosis (decreased FEV1/FVC ratio), as not all patients will have the classic symptoms noted above. When flow– volume loops (spirograms) are constructed, there is a classic “scooped-out” appearance during expiration in obstructive lung diseases like COPD. This is caused by the pathologic changes in the airways in which the expiratory flow rapidly decreases due to loss of elastic recoil, increased airway resistance, and collapse of small airways. (A) This is a normal flow–volume loop. (C) With restrictive lung diseases, the flow–volume loop is smaller and shifted to the right. This is caused by an increase in elastic recoil of the lung leading to decreased lung volumes. (D) In patients with a fixed upper airway obstruction (e.g., subglottic stenosis), there is a limit to the airflow that can be generated during inspiration and expiration because of the fixed narrowing of the airway. This is seen as a plateau in the flow–volume loop.