Effects of simulated tidal and deep breathing on immature airway contraction to acetylcholine and nerve stimulation

Background and objective: In adults, respiratory movements, such as tidal and deep breaths, reduce airway smooth muscle force and cause bronchodilation. Evidence suggests that these beneficial effects of oscillatory strain do not occur in children, possibly because of reduced coupling of the airways to lung tissue or maturational differences in the intrinsic response of the airways to oscillatory strain.Methods: The bronchodilator effects of oscillatory strain were compared in isolated airway segments from immature (3–4 weeks and 8–10 weeks old) and mature (18–20 weeks old) pigs. The lumen of fluid-filled bronchi was volume-oscillated to simulate tidal breaths and 0.5×, 2× and 4× tidal volumes. Contractions to acetylcholine and electrical field stimulation were recorded from the lumen pressure and were compared under oscillating and static conditions. Airway stiffness was determined from the amplitude of the lumen pressure cycles and the volume of oscillation.Results: Volume oscillation reduced contractions to acetylcholine and electrical field stimulation in an amplitude-dependent manner and the percentage reduction was the same for the different stimuli across all age groups. There was no difference in the relaxed dynamic stiffness of airways from the different age groups.Conclusions: The intrinsic response of the airway wall to equivalent dynamic strain did not differ in airways from pigs of different ages. These findings suggest that mechanisms external to the airway wall may produce age-related differences in the response to lung inflation during development.