Determinants of inspiratory muscle function in healthy children

BACKGROUND: Children are affected by disorders that have an impact on the respiratory muscles. Inspiratory muscle function can be assessed by means of the noninvasive tension–time index of the inspiratory muscles (TTI(mus)). Our objectives were to identify the determinants of TTI(mus) in healthy children and to report normal values of TTI(mus) in this population. METHODS: We measured weight, height, upper arm muscle area (UAMA), and TTI(mus) in 96 children aged 6–18 years. The level and frequency of aerobic activity was assessed by questionnaire. RESULTS: TTI(mus) was significantly lower in male subjects (0.095 ± 0.038, mean ± SD) compared with female subjects (0.126 ± 0.056) (p = 0.002). TTI(mus) was significantly lower in regularly exercising (0.093 ± 0.040) compared with nonexercising subjects (0.130 ± 0.053) (p < 0.001). TTI(mus) was significantly negatively related to age (r = −0.239, p = 0.019), weight (r = −0.214, p = 0.037), height (r = −0.355, p < 0.001), and UAMA (r = −0.222, p = 0.030). Multivariate logistic regression analysis revealed that height and aerobic exercise were significantly related to TTI(mus) independently of age, weight, and UAMA. The predictive regression equation for TTI(mus) in male subjects was TTI(mus) = 0.228 − 0.001 × height (cm), and in female subjects it was TTI(mus) = 0.320 − 0.001 × height (cm) . CONCLUSION: Gender, age, anthropometry, skeletal muscularity, and aerobic exercise are significantly associated with indices of inspiratory muscle function in children. Normal values of TTI(mus) in healthy children are reported.