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Flow-volume loops plot air velocity in relation to lung volume during a cycle of maximal inspiration and expiration.  This patient's flow-volume loop exhibits a leftward shift indicating increased total lung capacity and residual volume.  In addition, there is a characteristic "scooped-out" expiratory pattern consistent with the reduced expiratory flow rates seen in obstructive lung disease.  This hyperinflation and expiratory airflow obstruction occur in chronic obstructive pulmonary disease (COPD).  Airflow obstruction in COPD is partially due to anatomic narrowing of the bronchi (chronic bronchitis).  In addition, decreased lung elasticity resulting from destruction of interalveolar walls (emphysema) promotes dynamic compression of the airways during expiration (intrapleural pressure becomes greater than airway pressure), further contributing to expiratory airflow obstruction.

Hyperinflation in COPD also reduces the inspiratory reserve volume, limiting the maximal tidal volume.  This is especially true during exercise, when expiration time is limited.  Because patients with COPD require extra time for exhalation, increasing amounts of air can become trapped in the lungs during rapid breathing, leading to further reduction in tidal volume.  This is known as dynamic hyperinflation and is believed to be a major cause of dyspnea and exercise limitation in COPD.

(Choice A)  Alveolar hyaline membranes are seen in acute respiratory distress syndrome.  The pulmonary edema tends to reduce lung compliance, causing a restrictive flow-volume pattern (purple curve).

(Choice B)  Atelectasis due to extrinsic pulmonary compression may occur when the pleural cavity fills with air (ie, pneumothorax) or fluid (eg, exudate, blood).  Lung volumes and total lung compliance are likely reduced under such conditions, producing a restrictive flow-volume pattern.

(Choice D)  Diffuse intraalveolar hemorrhage tends to dilute alveolar surfactant, increasing alveolar surface tension and promoting alveolar atelectasis.  These changes would reduce lung volumes and lung compliance, resulting in a restrictive flow-volume pattern.

(Choice E)  Pulmonary fibrosis tends to decrease lung volume and compliance, producing a restrictive pattern.  In restrictive diseases, total lung capacity and residual volume are reduced.  The expiratory flow rate is increased relative to the low lung volumes but is reduced compared to normal peak expiratory flow rates.

(Choice F)  In pulmonary thromboembolism there is decreased perfusion but minimal effect on ventilation.  Therefore, the flow-volume curve will remain mostly normal.

Educational objective:
The flow-volume loop for chronic obstructive pulmonary disease is characterized by increased residual volume and total lung capacity, as well as a "scooped-out" expiratory pattern due to reduced expiratory flow rates.  Both airway narrowing due to chronic bronchitis and decreased elasticity due to emphysematous destruction of interalveolar walls are responsible for the hyperinflation and airflow limitation.