© 2005 American Thoracic Society
Progressive Decline in FRC in Infants: Physiology or Technology?From the Authors:We welcome initiatives to assess and validate infant lung function equipment and would willingly participate in any attempt to resolve queries or potential discrepancies. Due to lack of detail regarding the lung model and protocol used for in vitro and in vivo evaluation of the Jaeger MasterScreen BabyBody plethysmograph by Broughton and colleagues, it is difficult to comment on the results presented. Their data are in disagreement with previously published multicenter in vitro validation (1) of the same equipment using a carefully characterized and validated lung function model (2). In that study, volumes between 75 and 300 ml were measured with an accuracy of ± 2.5% (adhering to ATS/ERS guidelines [3]), and low volumes (50 ml or less) were overestimated by 9%. Accuracy was maintained over frequencies between 20–120 strokes per minute; hence the possibility of errors due to adiabatic artifacts seems unlikely. Careful direct comparison of the two lung models and the precise protocols would be necessary to resolve these differences. In vivo validation of infant lung function equipment is notoriously difficult, and we commend Broughton and coworkers for attempting to undertake such comparisons. While it would have been helpful to know within-subject rather than group mean results, the observed differences between FRC obtained by the two infant plethysmographs are exactly as we would have predicted (4), and do not in themselves help to identify what is the "correct" value. As healthy infants cannot be sedated purely for such comparisons or methodological studies, a true "gold standard" for FRCpleth in infants is nonexistent. We therefore wish to underline the key message of our original paper that the FRCpleth data presented from 32 healthy infants are robust for the technique and protocol as described, and need to be augmented with far more measurements, data that we are currently collecting.
In contrast to measurements in adults, in whom repeat measures using different types of equipment and software can be undertaken relatively easily, it is extraordinarily difficult to exclude potential sources of systematic bias from infant lung function equipment. Therefore, thorough in vitro assessments, development of reference data for the specific techniques and equipments, sufficient published methodological information to enable researchers to reproduce results in their own setting and measurements in appropriate prospectively recruited healthy control subjects are mandatory when studying infants. Indeed, in the Castile study (5) quoted by Broughton and coworkers, interpretation of results would have been severely biased without a prospective healthy control group, in whom the mean (SD) FRCpleth was found to be 1.1 (1.9) Z-scores lower than that predicted (i.e., The letter from Broughton and coworkers endorses the key message of our paper (4) that any equipment for infant lung function testing requires comprehensive validation both in vitro and in vivo, and that reference data not only needs to be specific for the equipment used, but should be continuously updated and re-evaluated in the light of technical and methodological progress. We would welcome the opportunity to undertake further collaborative work in this field.
University of Münster, Münster, Germany and Institute of Child Health, London, United Kingdom FOOTNOTES Conflict of Interest Statement: G.H. received a Jaeger MasterScreen BabyBody plethysmograph from VIASYS Healthcare and organized a scientific meeting financed by Abbott Virology. J.S. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
90%) from the authors' own reference data published 4 yr earlier using similar equipment and protocol (