Reference Equations for Maximal Respiratory Pressures in Healthy Children and Adolescents

Maximal respiratory pressures are key indicators of respiratory muscle strength; however, reference equations and cut-offs to define respiratory muscle weakness are scarce in the European paediatric population. The aim was to create sex-specific reference equations for maximal inspiratory and expiratory pressures (PImax/PEmax) in a large sample of healthy children and to objectively establish cut-offs to define respiratory muscle weakness.

A multicentre cross-sectional study was conducted across 14 Spanish centres. Healthy children aged 6-18 years, stratified by sex and age, were recruited. Maximal respiratory pressures were measured following standardized methodology in accordance with international guidelines. Reference equations were developed through multiple linear regression analyses. Age- and sex specific cut-offs for respiratory muscle weakness were determined using Z-scores≥1.645 standard deviation (SD) below group means.

The final sample included 513 subjects (257 boys; 11.5 [SD3.5] years). Reference equations are: (1) PImax: boys=-41.41+10.21*age+6.26*body mass index (BMI)-0.37*age*BMI; girls=125.96-0.34*age-0.41*age²-5.75*BMI+0.63*age*BMI; (2) PEmax: boys=20.93+5.23*age+2.93*BMI; girls=-12.67+11.98*age-0.39*age²+2.57*BMI. Cut-offs for respiratory muscle weakness are higher in boys and increase with age (p<.001). Depending on age, PImax cut-offs range from 46 to 85cmH₂O in boys and from 45 to 68cmH₂O in girls, while PEmax cut-offs span 54-98cmH₂O in boys and 57-85cmH₂O in girls.

This study provides new reference equations for PImax and PEmax derived from the largest dataset of normative values in European children and adolescents. It also establishes age-specific cut-offs to define respiratory muscle weakness. These findings will facilitate the identification of respiratory muscle weakness and the selection of candidates for targeted training programmes.