Reference Equations for Maximal Sniff Nasal Inspiratory Pressure in Healthy Children and Adolescents

Inspiratory muscle weakness presents significant diagnostic challenges, particularly in children. Maximal sniff nasal inspiratory pressure (SNIP) is complementary to maximal inspiratory pressure (PImax) for assessing inspiratory muscle strength. This study aims to establish reference equations and lower limits of normal (LLN) for SNIP in paediatric population and to compare SNIP and PImax values.

A multicentre cross-sectional study was conducted across 14 Spanish centres. Healthy children aged 6-18 years, stratified by sex and age, were recruited. Anthropometric and spirometric data were collected, and PImax and SNIP were measured following standardized procedures. Reference equations for SNIP were derived using multiple linear regression analysis. Sex- and age-specific LLN were calculated using Z-scores≥1.645 standard deviation (SD) below group means. Statistical comparisons between SNIP and PImax were performed using t-tests.

The final sample included 499 subjects (250 girls; 11.5 [SD 3.5] years). SNIP reference equations are: girls=123.6+0.72*age-0.38*age²-4.80*body mass index (BMI)+0.46*age*BMI; boys=58.71+0.13*age+2.22*BMI. LLN ranged from 51 to 62 and 49 to 51cmH₂O for boys and girls, respectively. SNIP values were significantly lower than PImax in both sexes (p<.001).

This study presents the largest paediatric SNIP dataset worldwide, enabling the derivation of reference equations and sex- and age-specific LLN for SNIP. These findings have important clinical implications, particularly for assessing inspiratory muscle strength in patients unable to perform PImax. Furthermore, the comparison between SNIP and PImax suggests that these tests are not interchangeable in the paediatric population, but rather provide complementary information.