© 2007 American Thoracic Society
Appropriate Interpretation of Lung Function and Exercise Capacity in a Longitudinal Follow-up of Preterm ChildrenTo the Editor:The recent article by Vrijlandt and colleagues (1) provides a welcome addition to the sparse literature dealing with long-term respiratory follow-up of preterm infants into adulthood (2). We are, however, concerned that due to the relatively small sample size and use of inappropriate reference data, some of the conclusions are not supported by the evidence provided. In particular, two specific sentences in the abstract could be misquoted if not taken in the context of the paper. First, it is stated in the abstract that there was no significant difference in lung function and exercise parameters between preterm subjects with and without bronchopulmonary dysplasia (BPD) (Table 4). This statement is based on post hoc subgroup analysis of 20 males (8 with BPD), and is therefore inadequately powered to detect important differences. This is illustrated in Tables 4 and E4, where large and potentially clinically and physiologically relevant differences failed to reach statistical significance. The authors should be more cautious with their conclusions since the use of p values alone with a small sample size can be misleading. Furthermore, the statement "mean lung function parameters were within normal range among survivors of preterm birth" merely emphasizes how inappropriate the selected reference data were in terms of predicting expected values. This is clearly illustrated in Table 2, where FEV1 was on average 10% higher and airway resistance 40% lower than predicted among the healthy control group. These observations should not only send a sharp warning to clinicians, who regularly interpret results and manage treatment on the basis of such prediction equations, but also highlight the need for much closer examination of the appropriateness of currently available pediatric reference data, particularly during the complex transition from childhood into adulthood (3). Although inappropriate reference equations were used, the study included a prospectively recruited control group. This allowed identification of important differences in lung function in survivors of preterm birth that would have otherwise been missed had the authors relied solely on published prediction equations. This study makes an important contribution to existing knowledge, but further funding should be sought to follow up a larger, more representative sample of the original cohort. Furthermore, this study highlights an urgent need for renewed international initiatives to develop more appropriate reference data, with modern statistical methods to facilitate interpretation of lung function results.
UCL Institute of Child Health, London, United Kingdom FOOTNOTES Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
