ventilation induces endogenous surfactant release in normal

noisy ventilation, which includes random breath-to-breath variations in tidal volume (VT) and frequency, has been shown to consistently improve blood oxygenation during me-chanical ventilation in various models of acute lung injury. To further understand the effects of variable ventilation on lung physiology and biology, we mechanically ventilated 11 normal guinea pigs for 3 h using constant-VT ventilation (n 6) or variable ventilation (n 5). After 3 h of ventilation, each animal underwent whole lung lavage for determination of alveolar surfactant content and composition, while protein content was assayed as a possible marker of injury. Another group of animals underwent whole lung lavage in the ab-sence of mechanical ventilation to serve as an unventilated control group (n 5). Although lung mechanics did not vary significantly between groups, we found that variable venti