Expiration is typically characterized as?

Expiration, in the context of respiratory physiology, is typically characterized as a passive process. This is because, during normal breathing, expiration does not require the active contraction of muscles. Instead, it occurs when the diaphragm and the intercostal muscles relax, allowing the elastic recoil of the lungs and thoracic cavity to push air out of the lungs. This recoil is a result of the natural elasticity of lung tissue and the thoracic wall.

In contrast, other terms associated with breathing processes, such as "active," "involuntary," and "forced," correlate with different aspects of respiration. Active expiration can occur during vigorous activities where additional muscles may be engaged to expel air more forcefully. Involuntary refers to automatic processes, but in the context of expiration, it does not emphasize the passive nature of the process itself. Forced expiration, on the other hand, involves actively contracting abdominal muscles and internal intercostal muscles to push air out quickly; however, this is not the typical or primary method of expiration under standard resting conditions.