What is emphysema characterized by?

Emphysema is characterized by the presence of permanently enlarged airspaces due to the destruction of alveolar walls, which is referred to as necrosis. This destruction leads to a decrease in the overall elasticity of the lung tissue, causing those air spaces to lose their ability to constrict properly. As a result, air becomes trapped in the lungs during exhalation, leading to inefficient gas exchange and contributing to the symptoms commonly associated with this condition, such as shortness of breath. The destruction of alveolar walls critically affects the lung's structure and function, resulting in significant impairment of respiratory mechanics.

While other options point to aspects related to lung function, they do not capture the specific pathology of emphysema as accurately as the characterization provided in the correct choice.