Dynamic Inspiratory Muscle Strength in Children with Cystic Fibrosis: Implications for Preoperative Assessment

Abstract

Background: Dynamic inspiratory muscle strength, quantified by the Strength Index (S-Index), reflects functional pressure generation during rapid inspiratory efforts. Although static respiratory measures, such as maximal inspiratory pressure and sniff nasal inspiratory pressure, are routinely used in the management of cystic fibrosis (CF), dynamic inspiratory parameters have not previously been characterized in pediatric CF populations. Objectives: This study aimed to evaluate dynamic inspiratory muscle function in children with CF using the S-Index and to compare the results with published normative data from healthy pediatric cohorts. Methods: This single-center, cross-sectional study enrolled 40 children with confirmed CF who underwent standardized dynamic inspiratory muscle assessment. The primary outcomes were the average and best S-Index values, peak inspiratory flow (PIF), and inspiratory volume. The CF cohort was compared with healthy reference values and further analyzed by sex and age group (≤ 12 vs. > 12 years). Results: The mean S-Index Best was 47.30 ± 20.35 cmH2O, which was significantly lower than the healthy reference value of 56.6 cmH2O (P = 0.012). The S-Index Avg was also reduced compared with normative data (36.35 ± 18.02 vs. 43.2 cmH2O; P = 0.035). PIF Best (2.52 ± 1.19 L/s) did not differ significantly from the reference value (P = 0.685). Male participants and older children (> 12 years) had significantly higher S-Index and PIF values than female participants and younger children (P = 0.002 and P < 0.001, respectively). Age was strongly correlated with S-Index. Conclusions: Children with CF showed mean reductions of 9.30 cmH2O (16.4%) in S-Index Best and 6.85 cmH2O (15.9%) in S-Index Avg compared with healthy norms, whereas flow parameters were relatively preserved. These findings suggest impaired dynamic inspiratory pressure generation in pediatric CF and support further investigation of inspiratory muscle assessment in perioperative respiratory evaluation. However, the clinical utility of the S-Index for perioperative risk stratification remains hypothesis-generating and requires prospective validation.