Relationships between Ventilator Waveform and Tidal-Volume Distribution

The relative performance of three volume-preset ventilators, each distinguished by a characteristic inspiratory flow waveform, was studied on a two-chambered lung model in which the entrance to one chamber was partially obstructed. The effects of alterations in rate and tidal volume on distribution by each of the ventilators were compared. The ventilators studied were Bennett MA-1, Emerson 3-PV, and Engstrom ER-312. This study determined that (1) the devices, because of differences in waveform, exhibited characteristic differences in the manner and time-sequence of volume distribution, (2) regardless of the character of the inspiratory waveform, changes in respiratory rate dramatically affect the distribution of tidal volume, (3) ventilator waveform had only a small effect on the volume delivered to the partially obstructed chamber, and (4) changes in tidal volume from 300 to 800 ml have only a small effect on distribution.