What is the key abnormal finding in a patient with chronic obstructive pulmonary disease (COPD)?

In a patient with chronic obstructive pulmonary disease (COPD), a key abnormal finding is decreased expiratory airflow. This condition is characterized by progressive airflow limitation due to the destruction of lung tissue and inflammation of the airways, which lead to narrowing. As a result, patients experience difficulty in exhaling air from the lungs, causing air trapping and leading to an increased residual volume.

Decreased expiratory airflow is often assessed using spirometry, which captures the reduction in the forced expiratory volume in one second (FEV1) relative to the forced vital capacity (FVC). This reduced FEV1/FVC ratio is an essential diagnostic criterion for COPD and reflects the underlying pathophysiological changes in the airways and lung parenchyma.

The other answer options do not accurately reflect the characteristic abnormalities seen in COPD. For instance, increased lung capacity is not typical for COPD; instead, patients often have reduced overall lung function. Normal arterial blood gases are unusual; patients typically show signs of respiratory acidosis or hypoxemia due to impaired gas exchange. Lastly, excessive lung compliance in COPD can describe the phenomenon of lung over-distension, but decreased elasticity is a more relevant concern when discussing the abnormal findings related to airflow limitation.