May 19, 1998 (Boston, Mass.) -- Physicians have long known that putting a patient with compromised breathing onto a ventilator is a double-edged sword. While the mechanical device undeniably prolongs life by breathing for the patient, it also can damage delicate lung tissue, and over time the ventilator's effectiveness in delivering oxygen to the blood may be considerably diminished.
In this week's edition of Nature, scientists at Boston University's Department of Biomedical Engineering report a new model of ventilator assisted lung function. In this model the pressure of the air delivered by the ventilator is varied by the addition of "noise," a random amount of additional air pressure which varies from breath to breath. This approach was first used by scientists at the University of Manitoba.
Based on new computer simulations developed at Boston University, the scientists now believe that the "noisy" ventilator not only has the potential to improve gas exchange in patients with lung injury but it may also minimize additional trauma.
Suki and his colleagues at Boston University developed a computer model of lung injury in which large regions of the lung are collapsed. They found that during inhalation, collapsed regions of the lung tend to open in a burst, or avalanche, with large groups of airways and alveoli popping open simultaneously, suddenly increasing the alveolar surface area available for gas exchange. They found that by varying the pressure of the air delivered by the ventilator -- adding "noise" to the base air pressure -- this avalanche-like opening of the airways and alveoli was enhanced and gas exchange was improved.
Furthermore, the scientists discovered there is an optimum amount of noise. Too much variability may lead to barotrauma (high pressure induced lung injury) while too little noise may have no effect at all.
This phenomenon is similar to noise-enhanced amplification of a useful signal via stochastic resonance, an effect that can be found in many neuronal systems. "We believe understanding the mechanism underlying this new mode of ventilation is important," says Suki, "because using the concept of stochastic resonance will allow us to optimize ventilation strategy for each individual." Suki and his colleagues are now testing this model on animals with promising preliminary results.
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