Sex-specific prediction equations for V̇maxFRC in infancy: A multicenter collaborative study

Ah Fong Hoo, Carol Dezateux, John P. Hanrahan, Tim J. Cole, Robert S. Tepper, Janet Stocks

Research output: Contribution to journalArticlepeer-review

95 Scopus citations


Measurements of maximal flow at functional residual capacity (V̇maxFRC) 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 V̇maxFRC results in both clinical practice and research. To address this problem, we collated V̇maxFRC 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 V̇maxFRC, which was, on average, 20% higher in girls than in boys during the first 9 months of life. V̇maxFRC)0.5 (ml · second-1) = 4.22 + 0.00210 × length2 (cm) for boys (RSD = 3.01; R2 = 0.48), and -1.23 + 0.242 × 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 V̇maxFRC 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 V̇maxFRC, during infancy should also improve interpretation of both clinical and research studies.

Original languageEnglish (US)
Pages (from-to)1084-1092
Number of pages9
JournalAmerican journal of respiratory and critical care medicine
Issue number8
StatePublished - Apr 15 2002


  • Forced expiratory flow
  • Infant
  • Reference values
  • Respiratory function tests
  • Sex

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine

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