Physiological Research on Variable Pressure Support Ventilation in Patients With Acute Acute Lung Injury: Part I and Part II

Noisy Pressure Support Ventilation (noisy-PSV) would lead to improved lung function, while preserving respiratory muscle unloading. Basically, noisy PSV differs from other assisted mechanical ventilation modes that may also increase the variability of the respiratory pattern (e.g. proportional assist ventilation) by the fact that the variability does not depend on changes in the patient's inspiratory efforts. The aim of this study is to evaluate the optimal variability for noisy PSV in patients with ALI based on its effects on respiratory mechanics, breathing comfort, gas exchange, and hemodynamics. The investigators hypothesize that noise in pressure support leads to variations in VT that are able to improve lung function and that physiologic variables respond differently to the degree of variability in pressure support