Normal values for maximal static inspiratory and expiratory pressures in healthy children.

Maximal static respiratory pressures are a simple measure of respiratory muscle strength. In order to construct a set of equations describing normal values, we measured maximal inspiratory (P(Imax)) and expiratory (P(Emax)) pressures in 296 children (144 boys and 152 girls), aged 7-14 years, in sitting and standing positions. The boys reached higher values in sitting and standing positions for P(Imax) (-8.29 +/- 2.69 and -8.19 +/- 2.73 kPa, respectively) and P(Emax) (8.02 +/- 2.32 and 7.94 +/- 2.32 kPa, respectively) than girls (-6.53 +/- 1.99 and -6.60 +/- 2.03 kPa for P(Imax) and 6.91 +/- 1.79 and 7.13 +/- 1.81 kPa for P(Emax) for sitting and standing positions, respectively); the differences between boys and girls were highly significant (P < 0.001 in all instances). There were no differences regarding body position during measurements in both genders. Multiple correlation analysis showed significant correlations of pressures to age in boys in all cases, but in girls only for P(Imax) in standing position. Therefore, equations describing reference values were constructed with respect to age as the independent variable. Maximal pressures also correlated with maximal inspiratory and expiratory flows. The measurements of P(Imax) and P(Emax) are useful in assessing respiratory muscle strength despite their relatively large variability. P(Imax) and P(Emax) also correlate with maximum peak expiratory and inspiratory flows. Children generate lower pressures and lower maximal flows than adolescents and adults.