ATYERS Workshop Summarv The Raised Volume Rapid Thoracoabdominal Compression Technique

Periodically, the Joint American Thoracic Society/European Respiratory Society Working Group on Infant Lung Function Testing publishes results of workshops on new techniques for lung function testing in infants. One such half-day workshop on forced expiratory flow-volume curves from raised lung volumes in infants was held by the Infant Lung Function Joint Working Group of the ATS and ERS immediately prior to the 1997 Annual Meeting of the American Thoracic Society in San Francisco. The workshop was organized by Monika Gappa and Julian Allen. Because there has been growing interest in this field since this workshop was held, a summary of this meeting, including some discussion of the physiology underlying these measurements, is now presented. A number of publications stemming from work presented during this workshop have either recently appeared or are in press. The purpose of this workshop was to help clarify discrepancies between different centers and facilitate subsequent development of standards that are necessary before this new approach of assessing airway function in infants and young children can be used widely as a clinical tool. In adults and school children, forced expiratory flow-volume curves over the full lung volume range have been used for many years to assess airway function. In infants, the rapid thoracoabdominal compression (RTC) technique was developed to obtain partial forced expiratory flow-volume curves (1, 2). In this technique, an inflatable vest around the infant’s chest and upper abdomen is rapidly pressurized at end inspiration, leading to a sudden forced expiration. Measurement of flow by a pneumotachograph attached to a face mask and integration to volume yield a partial forced expiratory flow-volume curve. Although this technique has yielded important information on airway physiology and pathophysiology in this age group, several disadvantages have become apparent. First, airway function is assessed in the tidal volume range only. Second, maximal flow at FRC (VmaxFRc) is highly variable; this is at least in part explained by the dynamically maintained functional residual capacity in infants such that there is no reliable volume landmark. Third, flow limitation is difficult to ascertain, especially in healthy infants. Recently, the raised volume rapid thoracoabdominal compression (RVRTC) technique has been developed, in which the infant’s lungs are inflated to a given airway pressure, using an external gas source (3) with or without an expiratory valve system (4, 5), before forced expiration begins. Available data are still sparse, but initial experiences with this modified technique have been promising. This is an exciting development because, for the first time, it is possible to generate flow-volume curves in infants that closely resemble flow-volume curves in older children and adults.