[Frequency dependance of compliance]

Resistance of peripheral or "small" airways is only a small part of the total pulmonary resistance (Raw). Even considerable obstruction in these airways will have little effect on total resistance. Conversely this will lead to inequality in the time constants of units in parallel, and dynamic lung compliance (C dyn) shall fall as respiratory frequence increases. C dyn is measured from simultaneous recordings of transpulmonary pressure (esophageal balloon) and volume obtained from a volume displacement plethysmograph. If Raw and static compliance are found to be normal, the frequency dependance of compliance will result from peripheral airway obstruction only. Early stages of chronic airway obstruction can be established by this method. However this appear not suitable for wide-scale studies.