Diaphragm contraction lowers pleural pressure during inspiration, increasing the pressure difference across the lung, known as the transpulmonary pressure gradient. This gradient supplies the distending force that expands lung tissue and permits air entry. Evaluating this relationship helps explain how respiratory muscle activity is translated into changes in lung volume during normal breathing.
Compliance describes how readily the lungs stretch when pressure changes, whereas airway resistance describes how strongly the airways oppose airflow. A change in compliance primarily alters the pressure needed to produce a given volume change, while resistance has a particularly important effect on airflow during expiration. Separating these properties improves interpretation of pressure and flow measurements.
Pressure-volume relationships show how changes in pressure correspond to changes in lung volume. Their pattern provides information about the mechanical behavior of the respiratory system, including how readily the lungs expand. In medicine, these relationships support assessment of abnormal mechanics and help connect measured respiratory behavior with diseases such as emphysema or pulmonary fibrosis.
Clinical assessment can include pressure-volume relationships, respiratory system compliance, and airway resistance. Together, these measurements examine distensibility, volume response, and opposition to airflow rather than relying on a single indicator. Comparing the results helps clinicians characterize respiratory function, interpret altered breathing mechanics, and identify findings relevant to conditions including asthma, emphysema, and pulmonary fibrosis.
Mechanical ventilation uses lung-mechanics principles to select airway pressures that support lung expansion without imposing unnecessary mechanical stress. Pressure and compliance information can help clinicians judge whether ventilation is producing adequate lung expansion or excessive distension. This approach is intended to reduce risks associated with overdistension while also avoiding inadequate lung expansion during assisted breathing.
Measurements of compliance, resistance, and pressure-volume behavior provide different mechanical perspectives on respiratory disease. These data can help clinicians interpret abnormalities associated with asthma, emphysema, and pulmonary fibrosis, although the conditions may affect measurements in different ways. Using several measurements together gives a more informative assessment than considering airflow, pressure, or volume alone.