Lesser used tests of pulmonary function: compliance, resistance and dead space.

The measurements of lung compliance, airway resistance and respiratory dead space as clinical tests have gradually fallen into disuse as the standard pulmonary function testing procedures; spirometry, lung volume and diffusing capacity measurement, followed, if necessary, by imaging have become the norm for diagnosis of COPD and other lung diseases. To have a real understanding of what spirometry and lung volume tests measure requires some knowledge of compliance and airway resistance. The respiratory dead space is an important global indicator of ventilation/perfusion relationships that remains of interest in the early detection of pulmonary emboli. There are other situations as well where it is clinically useful to perform the measurements described here, so these techniques, although generally set aside from the commonly used tests, should not be forgotten.