A99-08 Triple-Blind Randomized Clinical Trial on the Immediate Diaphragmatic Modulation Induced by Chest Physiotherapy Using Slow Passive Expiratory Techniques in Infants

Rationale Chest physiotherapy plays an established role in pediatric respiratory management; however, the specific diaphragmatic effects of passive expiratory techniques remain poorly understood. Prolonged Slow Expiration (PSE), Slow Expiratory Flow Increase (SEFIT), and Assisted Autogenic Drainage (AAD) are widely used in clinical practice. However, their effects on diaphragmatic contractility have not been quantitatively demonstrated. We hypothesized that, compared with a sham procedure, slow-flow passive techniques would immediately enhance diaphragmatic contractility and inspiratory performance in infants. Methods This triple-blind, parallel-group, randomized controlled trial followed the 2025 CONSORT guidelines and was approved by the institutional ethics committee. The trial was prospectively registered with the Brazilian Registry of Clinical Trials (ReBEC) (Identifier: RBR-9nt4gj). Eighty healthy infants (aged 2-6 months) were randomly assigned to one of four groups: PSE, SEFIT, AAD, or a sham intervention. Allocation concealment and blinding were implemented for therapists, outcome assessors, and data analysts. Each participant received a single, standardized, five-minute session of the assigned intervention. Primary outcomes were diaphragmatic contraction velocity (DCV, mm/s) and diaphragm thickening fraction (DTF, %); these were assessed via ultrasonography before and immediately after the intervention. Secondary outcomes included relaxation velocity and diaphragmatic excursion. Analyses were performed using a two-way mixed ANOVA (group × time) with a Tukey post hoc correction and partial eta-squared (η2) for effect size and 95% confidence intervals (CIs). Results Baseline characteristics were comparable across groups (p > 0.05). Significant group × time interactions were observed for diaphragmatic contraction velocity (DCV; F [3,76]=7.12, p < 0.001, η2=0.21) and thickening fraction (DTF; F[3,76]=5.48, p = 0.002, η2=0.17). Compared with the sham procedure, Prolonged Slow Expiration (PSE) increased DCV by + 6.1 mm/s (95% CI 3.2-8.9; p < 0.001), while Slow Expiratory Flow Increase (SEFI) showed a trend toward greater inspiratory thickness (Δ + 0.22 mm; 95% CI 0.01-0.43; p = 0.054), as shown in figure 1. No significant changes were detected in diaphragmatic excursion (p = 0.28). Conclusion Slow-flow passive techniques produced immediate and measurable improvements in diaphragmatic contractility in healthy infants. Prolonged slow expiration elicited the most significant enhancement in contraction velocity, suggesting an acute neuromechanical response of the diaphragm to gentle expiratory loading. These findings provide the first quantitative evidence that specific chest physiotherapy maneuvers can transiently optimize inspiratory muscle performance during early infancy. This supports the physiological relevance and translational potential of these maneuvers in pediatric respiratory care.