AIRWAY MUSCLE IN PRETERM INFANTS - CHANGES DURING DEVELOPMENT

Objective: To quantitate airway muscle changes in infants born at 23 t o 41 weeks' gestation (control subjects) and to compare the changes wi th those in infants with chronic lung disease, Methods: Fifty-five hum an lungs (from infants born at 23 to 41 weeks' gestation) were studied : 46 from infants who died of various diseases within 72 hours of birt h, and 9 from infants with CLD (infants born at 26.9 +/- 0.5 weeks' ge station, who lived 17 +/- 8 days). All the lungs were perfused via the trachea and pulmonary artery in a standardized protocol, Formalin-fix ed tissues in paraffin blocks were cut 5 mu m thick, Sections were imm unohistochemically stained for alpha-smooth muscle actin, By using com puterized image analysis to quantitate images digitized into the compu ter, we measured the area of muscle, epithelium, airway lumen, and len gth of basement membrane in 18 airways, from the smallest bronchioles to bronchi, in each infant, Results: Muscle was present at 23 weeks' g estation at all levels of the bronchial tree, and from 25 weeks to ter m the control lungs had a similar quantity of muscle at any given airw ay circumference, Relative to airway size, there was more muscle in sm all airways, less than 1000 mu m in circumference, than in larger airw ays, In airways greater than 1500 mu m in circumference, infants with CLD had significantly more muscle than did control lungs, Conclusions: Airway muscle is present at 23 weeks' gestation at all levels of the conducting airways, The 25-week gestation infants had a quantity of ai rway muscle relative to airway circumference similar to that of term i nfants, Preterm infants with CLD who were aged 9 to 29 days have incre ased airway muscle in airways greater than 1500 mu m in circumference; Bronchospasm in very low birth weight infants is possible within the first days of life.