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Sex-specific prediction equations for Vmax(FRC) in infancy: a multicenter collaborative study
Ah-Fong Hoo1, Carol Dezateux, John P Hanrahan
1Portex Anaesthesia, Intensive Therapy and Respiratory Medicine Unit, Institute of Child Health and Great Ormond Street Hospital for Children National Health Service Trust, London, UK. a.hoo@ich.ucl.ac.uk
Insights
Maximal flow at functional residual capacity (Vmax(FRC)) measurements assess infant small airway function. New sex-specific reference data improve accuracy, preventing misdiagnosis in boys and missed changes in girls.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Infant Lung Function Testing
Background:
- Maximal flow at functional residual capacity (Vmax(FRC)) is a key indicator of small airway function in young children.
- Existing Vmax(FRC) reference data lack broad applicability and fail to capture normal variability, hindering clinical and research interpretation.
- Accurate reference data are crucial for reliable assessment of infant respiratory health.
Purpose of the Study:
- To develop sex-specific reference equations for Vmax(FRC) in infants.
- To improve the interpretation of Vmax(FRC) measurements in clinical practice and research.
- To establish reliable z scores for assessing normal Vmax(FRC) ranges during infancy.
Main Methods:
- Collated Vmax(FRC) data from 459 healthy infants (first 20 months of life) across three centers.
- Utilized multiple linear regression analysis to identify predictors of Vmax(FRC).
- Developed sex-specific prediction equations based on infant length and age.
Main Results:
- Sex, age, and length were significant predictors of Vmax(FRC).
- Vmax(FRC) was approximately 20% higher in girls than boys in the first 9 months.
- Sex-specific equations were derived: (Vmax(FRC))^0.5 = 4.22 + 0.00210 * length^2 (cm) for boys and -1.23 + 0.242 * length (cm) for girls.
- Alternative models incorporating age and length z scores were also developed.
Conclusions:
- Using sex-specific prediction equations for Vmax(FRC) is essential for accurate interpretation in infants.
- Failure to account for sex can lead to misdiagnosis of airway function in both boys and girls.
- Implementing z scores for Vmax(FRC) will enhance the reliability of infant respiratory assessments.
Abstract:
Measurements of maximal flow at functional residual capacity (Vmax(FRC)) from partial forced expiratory maneuvers remain the most popular method for assessing small airway function in infants and young children. However, the lack of appropriate reference data that are both applicable outside the centers that developed them and reflect the normal variability between healthy subjects has limited interpretation of Vmax(FRC) results in both clinical practice and research. To address this problem, we collated Vmax(FRC) data from 459 healthy infants (226 boys) tested on 654 occasions during the first 20 months of life from three collaborating centers. Multiple linear regression analysis indicated that sex, age, and length were important predictors of Vmax (FRC), which was, on average, 20% higher in girls than in boys during the first 9 months of life. (Vmax(FRC))0.5 (ml x second(-1)) = 4.22 + 0.00210 x length2 (cm) for boys (RSD = 3.01; R2 = 0.48), and -1.23 + 0.242 x length for girls (RSD = 2.72; R2 = 0.49). Alternative models incorporating both age and length z scores are also described. Failure to use sex-specific prediction equations for Vmax(FRC) may preclude detection of clinically significant changes in girls and lead to false reports of diminished airway function in boys. Appropriate use of z scores, which indicate a "normal" range (z scores of 0 +/- 2) for Vmax(FRC), during infancy should also improve interpretation of both clinical and research studies.