Maximal flow at functional residual capacity in healthy children from birth to 7 years, and beyond

Background: Reference values for maximal expiratory flows throughout childhood have been developed for each age group, but it remains a challenge to find a single outcome measure that can be tracked from birth to childhood. We believe that maximal flow at functional residual capacity (FRC)(V̇maxFRC) may be a good candidate. The aim of this article was to explore the possible use of V̇maxFRC as a continuous measure in healthy infants and children of preschool age. Methods: Original spirometric data from healthy infants and preschool children in previously published studies from four centers around the world were reanalyzed (N = 242; ages 0-7 years). In preschool children, V̇maxFRC was extracted by reanalysis of available records. Multiple regression analysis was applied to find the best correlation between maxFRC and height, weight, and/or age. maxFRC values were also compared with previously published data from healthy populations of similar ages. Results: V̇maxFRC highly correlated with height from infancy to childhood: Ln { V̇maxFRC [L/s ]} = - 11.99 + (2.561 X Ln{Length[cm]}), where Ln is natural logarithm; r = 0.90; SE = 0.355; P<.0001. Adding weight but not age improved the correlation slightly (r = 0.91). V̇maxFRC values were not affected by sex, maneuver modality (passive or voluntary), body posture, or degree of sedation. We found very good agreement between our calculated V̇maxFRC values and the extrapolated V̇maxFRC values from reference data of similar and older populations. Conclusions: V̇maxFRC can be easily extracted from spirometry and can potentially serve as a continuous spirometric parameter for describing maximal flow at low lung volumes. Further studies are needed to confirm V̇maxFRC values in a wider age range in health and disease.