Can a single equation be used to predict the vital capacity of boys both before and during puberty?

Good theoretical values for vital capacity (VCt) can be used to calculate a VC/VCt ratio which remains constant for a given individual subject throughout different growth periods. This longitudinal study on 27 boys was performed in order to determine whether a single equation was accurate throughout the growth of boys. The mean values of VC/VCt were also compared for the beginning and end of the prepubertal period in 57 boys and between the beginning and end of puberty in 40 boys. VCt was calculated from five reference equations using data from boys with average age 8-16 yrs, and from two equations using data specific to children and adolescents. The mean VC/VCt ratio was found to fall between the beginning and end of the prepubertal period and to increase very significantly between the beginning and end of the pubertal period when the reference equation used had been calculated using data from populations containing both pubertal and prepubertal subjects. When the equations established from adolescents were used, VC/VCt fell slightly between the beginning and end of the pubertal period. We conclude that data for children and adolescents should be treated separately when establishing reference values for VC.