COMPLIANCE

The elastic properties of the lung and relaxed chest wall are determin ed 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 wal l and are useful in evaluating patients with a variety of disease stat es, The slope of the lung's static PV curve (Delta volume/Delta pressu re) 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-inspirat ion and end-expiration at instants of zero flow. Assessment of these p ulmonary characteristics with esophageal balloon measurements in spont aneously breathing patients has not been routine in clinical practice but has gained new popularity in evaluating patients with emphysema fo r lung volume reduction surgery (LVRS), Such measurements may help to predict which patients will benefit from surgery and to assess physiol ogical responses to surgery, Furthermore, measurement of PV curves in the patient with acute respiratory failure requiring assisted mechanic al ventilation provides diagnostic, therapeutic, and prognostic inform ation, This article will review the physiology, measurement techniques , and clinical applications of Cst and Cdyn and chest wall compliance.