Compliance

Abstract

The elastic properties of the lung and relaxed chest wall are determined by connective tissue forces and surface tension at the alveolar air-liquid interface. These properties are characterized by the shape and position of the pressure volume (PV) curves of the lung and chest wall and are useful in evaluating patients with a variety of disease states. The slope of the lung's static PV curve (Δvolume/Δpressure) is the static compliance (Cst) of the lung; it reflects the change in volume caused by a given change in inflation pressure of the lung parenchyma. Dynamic lung compliance (Cdyn) is measured at end-inspiration and end-expiration at instants of zero flow. Assessment of these pulmonary characteristics with esophageal balloon measurements in spontaneously breathing patients has not been routine in clinical practice but has gained new popularity in evaluating patients with emphysema for lung volume reduction surgery (LVRS). Such measurements may help to predict which patients will benefit from surgery and to assess physiological responses to surgery. Furthermore, measurement of PV curves in the patient with acute respiratory failure requiring assisted mechanical ventilation provides diagnostic, therapeutic, and prognostic information. This article will review the physiology, measurement techniques, and clinical applications of Cst and Cdyn and chest wall compliance.