Final answer:
In pulmonary function tests, an obstructive lung disease is indicated by a lower FEV1/FVC ratio (less than 69 percent), reflecting decreased airflow due to airway obstruction from conditions such as COPD, emphysema, or asthma.
Step-by-step explanation:
The components of Pulmonary Function Tests (PFT) that indicate an obstructive disease are primarily focused on the measurements of Forced Expiratory Volume in one second (FEV1) and the Forced Vital Capacity (FVC). An obstructive lung disease, such as Chronic Obstructive Pulmonary Disease (COPD), emphysema, or asthma, is characterized by reduced airflow due to obstruction. This is detected by a lower FEV1/FVC ratio (less than 69 percent) compared to restrictive diseases where the ratio is higher (88 to 90 percent). In cases of obstructive disease, patients exhibit increased lung compliance due to the destruction of alveolar walls in emphysema or increased inflammation and mucus production in asthma, which leads to airway obstruction and trapping of air resulting in high lung volumes upon exhalation.