Lung function--clinical importance, problems, and new results.

This review tackles the usefulness of spirometry, a more than century old method of assessing pulmonary lung function. Variables measured with a spirometer, such as forced expiratory volume in 1 s, have long been the mainstays of the diagnosis and treatment of lung disorders. But there are problems with the reliability of spirometric measurements. The method depends on the cooperation of the investigated subject, which introduces a confounding subjective element and all too often results in test failure, and the results are evaluated against the predicted values that are based on a set of fixed factors, some of which, such as body height, are not in a straight proportion to the intrathoracic gas volume. Substantial spread of results arises, which makes a reliable assessment of lung function difficult. New methods, such as the resistance-volume curve, provide better information on airway behavior in different conditions. These new methods, which basically evolved from spirometry, show that the old idea of lung function analysis is still viable and may remain helpful for diagnosis and treatment of respiratory pathological states.