A 61-year-old man is evaluated for progressive exertional dyspnea and decreased exercise tolerance. He has also noticed some ankle swelling. The patient has a 40-pack-year smoking history but no illicit drug use or occupational exposure. Examination shows increased anteroposterior diameter of the chest. Breath sounds are decreased throughout. Heart sounds are distant. The abdomen is soft and nontender. Mild bilateral ankle edema is present. His chest x-ray is shown below. Which of the following is the most likely effect of the abnormal diaphragmatic contour in this patient?

Question

A 61-year-old man is evaluated for progressive exertional dyspnea and decreased exercise tolerance.  He has also noticed some ankle swelling.  The patient has a 40-pack-year smoking history but no illicit drug use or occupational exposure.  Examination shows increased anteroposterior diameter of the chest.  Breath sounds are decreased throughout.  Heart sounds are distant.  The abdomen is soft and nontender.  Mild bilateral ankle edema is present.  His chest x-ray is shown below.  Which of the following is the most likely effect of the abnormal diaphragmatic contour in this patient?

Quizplus · Accepted Answer

This patient's presentation suggests chronic obstructive pulmonary disease (COPD). Chest x-ray reveals increased radiolucency of the lung parenchyma, an elongated and narrow heart shadow, barrel-shaped chest, and a flat diaphragm, which are all the result of air trapping and progressive hyperinflation. Hyperinflation in COPD occurs through both static and dynamic mechanisms. The negative pressure created by the chest wall (expanding pressure) and the positive pressure created by the lungs (collapsing pressure) are in equilibrium at the functional residual capacity (FRC). In COPD, decreased elasticity of the alveoli results in decreased positive (collapsing) pressure created by the lungs to expel air. Consequently, the alveoli retain more air volume. At the increased lung volume, this decrease in positive (collapsing) pressure created by the lungs is balanced by a decrease in negative (expanding) pressure created by the chest wall. New pressure equilibrium is reached at a higher lung volume (higher FRC). The dynamic mechanism is comparatively more responsible for hyperinflation in COPD. It occurs through a phenomenon of "air stacking." The expiratory phase is prolonged in patients with COPD due to an increase in airway resistance. When exertional demands trigger an increase in minute ventilation (breaths per minute × tidal volume), the patient is forced to begin inhalation prior to completion of exhalation. The result is additional air trapping and hyperinflation. The diaphragm is the most important muscle for enlarging the thoracic cavity and creating negative pressure during inhalation. In COPD, the diaphragmatic flattening and muscular shortening caused by hyperinflation result in more difficulty in decreasing intrathoracic pressure during inspiration and therefore increase the work of breathing. (Choice A) Compliance is defined as change in volume per change in pressure and is the inverse of elasticity. Therefore, elasticity decreases in COPD and compliance increases. Flattening of the diaphragm is the result of increased lung compliance and does not lead to a decrease in lung compliance. (Choices B and C) COPD patients have significant airflow limitation with reduced inspiratory and expiratory flow rates. (Choice D) Hyperinflation leads to both increased thoracic wall recoil and flattening of the diaphragm. However, thoracic wall recoil is not directly due to diaphragmatic flattening. Educational objective: Decreased alveolar elasticity in chronic obstructive pulmonary disease causes lung hyperinflation, which results in increased total lung capacity, functional residual capacity, and residual volume, as well as diaphragmatic flattening. The flattened diaphragm has more difficulty contracting to expand the thoracic cavity, resulting in increased work of breathing. References: COPD exacerbations. 3: pathophysiology. (http://www.ncbi.nlm.nih.gov/pubmed/16565268) Why does the lung hyperinflate? (http://www.ncbi.nlm.nih.gov/pubmed/16565428)

A 61-Year-Old Man Is Evaluated for Progressive Exertional Dyspnea and Decreased