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-dependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equipment, the plethysmographic method for measuring FRC is very simple to apply and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further advantage that with suitable adaptations to the equipment, simultaneous measurements 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 help to ensure that such measurements are as accurate as possible and that meaningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects including terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus can be reached.