Mechanical ventilation of rat lung: effect on surfactant forms

Mechanical ventilation of the lung could affect surfactant turnover by alte ration of its secretion, recycling, and degradation. In vitro studies of su rfactant subfractions recoverable from lavage fluid have led to predictions about surfactant physiology in vivo that include morphological transformat ions. We used electron microscopy to study in situ lipid forms in alveoli o f rat lungs after two ventilation strategies [15 min at pressures (cmH(2)O) 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 hypopha se 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 double d after ventilation at 20/0, but VF were the same as control after ventilat ion at 20/10. The results showed that a ventilation pattern of 20/0 compare d with that of 20/10 group was associated with a significantly larger VF, s uggesting an increased net production of these surfactant forms during a la rge tidal volume breathing pattern. These morphological results are consist ent with published results using physical methods of fractionating lung lav age.