American Board of Internal Medicine (ABIM) Certification Practice Exam

What spirometry pattern is indicative of asthma?

1. Restrictive pattern

2. Obstructive pattern

3. Normal pattern

4. Mixed pattern

The correct answer is: Obstructive pattern

Asthma is characterized by a reversible obstructive pattern on spirometry. In an obstructive pattern, the hallmark finding is a reduced forced expiratory volume in one second (FEV1) compared to forced vital capacity (FVC), resulting in a lower FEV1/FVC ratio. This reflects the difficulty in exhaling air from the lungs, which is a primary feature of asthma. The obstruction in airflow seen in asthma is usually reversible, meaning that symptoms can improve significantly with bronchodilators, further solidifying the diagnosis. In contrast, a restrictive pattern is typically seen in conditions where lung volume is reduced, such as in interstitial lung disease or pulmonary fibrosis, where the FEV1 and FVC proportionally decrease, keeping the FEV1/FVC ratio relatively normal. A normal pattern would indicate that there is no obstructive or restrictive pathology present, while a mixed pattern indicates features of both obstruction and restriction, often seen in complex cases but not characteristic of asthma alone. Therefore, the identification of an obstructive pattern during spirometry is key to diagnosing asthma.