Investigation of the spontaneous modes of breathing of different ventilators.

We investigated six ventilator systems which were designed to allow spontaneous breathing. The time delay between initiation of inspiratory effort and the beginning of inspiratory gas flow was measured, as was the amount of negative (to ambient) pressure generated in the airway needed to produce the gas flow. We found that the flow-by program of the Puritan-Bennett 7200 caused minimal time delay and virtually no negative pressure was required to instigate gas flow. This should be contrasted with the other ventilator systems, which caused significant delay and inspiratory effort and hence increased work of breathing.