Plethysmographic measurements of lung volume and airway resistance

Functional residual capacity (FRC) is the only static lung volume that can be measured routinely in infants. It is important for interpreting volume-d ependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equi pment, the plethysmographic method for measuring FRC is very simple to appl y and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further adv antage that with suitable adaptations to the equipment, simultaneous measur ements of airway resistance can also be obtained. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for plethysmographic measurements in infants. Implementation of these recommendations should hel p to ensure that such measurements are as accurate as possible and that mea ningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects inclu ding terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus tan be reached.