Certified Respiratory Therapist Practice Exam

What is the primary characteristic of obstructive lung disease as seen in pulmonary function tests?

1. Increased FEV1

2. Decreased FEV1/FVC ratio

3. Normal FEV1/FVC ratio

4. Decreased Total Lung Capacity

The correct answer is: Decreased FEV1/FVC ratio

In obstructive lung disease, the primary characteristic observed in pulmonary function tests is a decreased FEV1/FVC ratio. This occurs because the forced expiratory volume in one second (FEV1) is significantly reduced due to airway obstruction, while the forced vital capacity (FVC) can be either normal or reduced but tends to be less affected than the FEV1. As a result, when FEV1 is compared to FVC, the ratio diminishes, indicating that a larger proportion of the total air capacity cannot be forcibly exhaled in one second due to the obstruction. This decreased ratio is a hallmark of conditions such as chronic obstructive pulmonary disease (COPD) and asthma, which impede airflow during expiration. Understanding this concept is crucial for diagnosing and managing patients with pulmonary disorders, as the FEV1/FVC ratio provides insight into the presence and severity of obstruction within the respiratory system.