What does the term compliance (C) measure?

Compliance (C) is a crucial pulmonary function parameter that measures the ease with which the lungs and thoracic structures can be distended or expanded in response to pressure changes during ventilation. When compliance is high, it indicates that the lungs can easily expand with minimal pressure, reflecting healthy lung tissue and adequate surfactant function. This concept is important in mechanical ventilation and respiratory physiology as it helps clinicians understand how much work is required to inflate the lungs.

In contrast, resistance of airflow refers to the opposition that air encounters while moving through the airways, which is a separate measure that assesses how easily air can travel into and out of the lungs. The return of a structure to its original form relates to the elasticity of lung tissue, while the work output of the lungs is concerned with the amount of energy expended during ventilation. Therefore, compliance specifically focuses on the distensibility of the lung structures rather than these other aspects of respiratory function.