Ontogeny of the ovine airway wall from late gestation to adulthood

Introduction: Airway disease presents both early and late in life. Knowledge on how physiological properties of airways change through the natural course of life is important to better understand mechanisms producing abnormal airway function. Aim: Measure physiological properties of bronchi from late gestation to adulthood in an ovine developmental model. Methods: Fetal (135-140 d gestation, n=5), four month (n=4), one year (n=7) and five year sheep (9adult9, n=6) were studied. Following euthanasia, a main stem bronchus was dissected and mounted in an organ bath chamber. Airway narrowing capacity (% volume) to acetylcholine was measured in bronchial segments. Collapsibility (pressure to closure) was determined before and after relaxation to theophylline or contraction to acetylcholine. Passive compliance (0-20 cmH 2 O) was measured after theophylline. Results: Collapsibility of fetal bronchi was greater than four month (P Conclusion: Collapsibility of bronchi falls during early development, consistent with structural maturation. The airway stiffens further later in life with the development of intrinsic airway smooth muscle tone. Separate processes contribute to early and late changes in airway mechanics which may be of relevance to the onset and trajectory of disease.