A 54-year-old man comes to the office due to shortness of breath that has slowly worsened over the last 6 months. He also has a persistent, nonproductive cough. The patient does not use alcohol, tobacco, or illicit drugs. Temperature is 36.8 C (98 F), blood pressure is 132/78 mm Hg, pulse is 74/min, and respirations are 16/min. Physical examination reveals fine crackles bilaterally on pulmonary auscultation and drumstick-shaped fingers. Chest x-ray reveals diffuse reticular opacities. Pulmonary function testing shows decreased FVC, increased FEV1/FVC ratio, and expiratory flow rates that are higher than normal when corrected for lung volume. This patient's supernormal expiratory flow rates are best explained by an increase in which of the following parameters?

Question

A 54-year-old man comes to the office due to shortness of breath that has slowly worsened over the last 6 months.  He also has a persistent, nonproductive cough.  The patient does not use alcohol, tobacco, or illicit drugs.  Temperature is 36.8 C (98 F), blood pressure is 132/78 mm Hg, pulse is 74/min, and respirations are 16/min.  Physical examination reveals fine crackles bilaterally on pulmonary auscultation and drumstick-shaped fingers.  Chest x-ray reveals diffuse reticular opacities.  Pulmonary function testing shows decreased FVC, increased FEV1/FVC ratio, and expiratory flow rates that are higher than normal when corrected for lung volume.  This patient's supernormal expiratory flow rates are best explained by an increase in which of the following parameters?

Quizplus · Accepted Answer

11ec160b_3cde_fa0b_9249_e164bee10673_MD0001_00 This patient's clinical presentation (progressive dyspnea, fine crackles, clubbing, diffuse reticular opacities) is consistent with interstitial lung disease (ILD). Most ILDs cause progressive pulmonary fibrosis with thickening and stiffening of the pulmonary interstitium. This causes increased lung elastic recoil, as well as airway widening due to increased outward pulling (radial traction) by the surrounding fibrotic tissue. The resulting decrease in airflow resistance leads to supernormal expiratory flow rates (higher than normal when corrected for lung volume). Additional pulmonary function test findings in restrictive lung diseases include reduced total lung capacity, vital capacity, inspiratory capacity, functional residual capacity, and residual volume. The FVC and FEV1 are decreased as well. However, the FEV1/FVC ratio is typically normal or increased as FEV1 decreases less than FVC (due to airway widening relative to the low lung volumes). In addition, fibrosis causes a reduction in the diffusion capacity of carbon monoxide. (Choice A) Lung compliance is defined as the change in lung volume for a given change in pressure. Increased compliance means that the lung tissue stretches and expands more in response to increased pressure. Restrictive lung diseases cause decreased lung compliance and lower lung volumes due to interstitial fibrosis. (Choice B) The outward recoil of the chest wall limits the volume of air that can be expired during maximal exhalation. An increase in outward chest wall recoil would decrease expiratory flow rates, as the respiratory muscles must work harder during expiration to oppose the increased outward force. (Choice C) Physiological dead space refers to the volume of inspired air that does not participate in gas exchange. Changes in the amount of physiological dead space can affect alveolar ventilation but do not affect expiratory flow rates. (Choice E) Thickening of the bronchioles, which occurs in some obstructive lung diseases (eg, asthma), leads to narrowing of the airways. Although reduced airway radius leads to local increase in airflow velocity, overall the increased resistance causes a decrease in expiratory flow rates. In fibrotic lung disease, the interstitium, not the bronchiolar walls, is thickened. Educational objective: Interstitial lung disease is associated with decreased lung volumes and increased lung elastic recoil caused by fibrotic interstitial tissue. The increased elastic recoil results in increased radial traction (outward pulling) on the airways, leading to increased expiratory flow rates when corrected for the low lung volume.

A 54-Year-Old Man Comes to the Office Due to Shortness