Mechanical ventilation of rat lung: effect on surfactant forms

Mechanical ventilation of the lung could affect surfactant turnover by alteration of its secretion, recycling, and degrada-tion. In vitro studies of surfactant subfractions recoverable from lavage fluid have led to predictions about surfactant physiology in vivo that include morphological transforma-tions. We used electron microscopy to study in situ lipid forms in alveoli of rat lungs after two ventilation strategies [15 min at pressures (cmH2O) of 20/0 or 20/10]. In control animals, 4% of the lipid profile area in the surface lining layer was myelin figures (MF), 14 % was tubular myelin, 37 % was vesicular forms (VF), and the remainder (45%) was hypophase. Com-pared with controls, the length-normalized sum of the lipid forms and the hypophase was two times as great in the lungs of the 20/0 group. MF were threefold higher in the 20/0 group and fivefold higher in the 20/10 group. VF doubled afte