Noise added to mechanical ventilation improves gas exchange in acute lung injury

Noise can be added to tidal volume (V/sub /spl tau//) to vary the depth of inspiration from cycle to cycle, called noisy volume ventilation (NVV), or noise can be added to peak inspiratory pressure from breath to breath, called noisy pressure ventilation (NPV). Experiments were done in two groups of guinea pigs. Guinea pigs with acute lung injury induced by endotoxin (LPS) inhalation or saline lavage. Both groups were mechanically ventilated alternating between periods of conventional ventilation (CV) or different degrees of noisy ventilation (NV). The authors found that the animals consistently showed significant improvement in gas exchange (increased PaO/sub 2/) and lung mechanics (decreased elastance) after NV. The NPV mode was the most efficient, and the degree of improvement was dependent on the level of noise applied, with an optimal level of 30-40%. These results are in agreement with the possibility of mechanical stochastic resonance in the gas exchange mechanism of the injured lung.