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

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) (VmaxFRC) may be a good candidate. The aim of this article was to explore the possible use of VmaxFRC as a continuous measure in healthy infants and children of preschool age.

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, VmaxFRC was extracted by reanalysis of available records. Multiple regression analysis was applied to find the best correlation between VmaxFRC and height, weight, and/or age. VmaxFRC values were also compared with previously published data from healthy populations of similar ages.

VmaxFRC highly correlated with height from infancy to childhood: Ln{VmaxFRC [L/s]} = -11.99 + (2.561 × 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). VmaxFRC 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 VmaxFRC values and the extrapolated VmaxFRC values from reference data of similar and older populations.

VmaxFRC 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 VmaxFRC values in a wider age range in health and disease.