Which pattern is seen in pulmonary function tests in a patient with interstitial lung disease?
**Core Concept**
Interstitial lung disease (ILD) is characterized by inflammation and fibrosis of the lung parenchyma, leading to impaired gas exchange and lung function. The pathophysiology involves damage to the alveolar-capillary membrane, resulting in decreased lung compliance and increased resistance to airflow.
**Why the Correct Answer is Right**
In patients with ILD, pulmonary function tests (PFTs) typically show a restrictive pattern. This is due to the loss of lung elasticity and increased stiffness of the lung parenchyma, leading to reduced lung volumes and capacities. The forced vital capacity (FVC) is decreased, while the forced expiratory volume in one second (FEV1) is relatively preserved. The ratio of FEV1 to FVC is usually normal or increased, which helps to distinguish ILD from obstructive lung diseases.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because obstructive lung diseases, such as chronic obstructive pulmonary disease (COPD), are characterized by a different pattern of lung function abnormalities, including decreased FEV1 and increased FEV1/FVC ratio.
**Option B:** This option is incorrect because pulmonary fibrosis, a type of ILD, is not typically associated with an increased FEV1/FVC ratio.
**Option C:** This option is incorrect because bronchiectasis, a condition characterized by dilated bronchi, is associated with an obstructive pattern of lung function abnormalities, including decreased FEV1 and increased FEV1/FVC ratio.
**Clinical Pearl / High-Yield Fact**
A classic exam trap in PFTs is distinguishing between restrictive and obstructive lung diseases. Remember that in restrictive lung diseases, the FEV1 is relatively preserved, while in obstructive lung diseases, the FEV1 is decreased.
**Correct Answer:** C.