Fluidic cycling devices for inspiratory and expiratory timing in automatic ventilators

The theoretically desirable characteristics of fluidic timing devices for use in automatic ventilators are discussed. The principal limitation of most timers described is the separate control of inspiratory and expiratory time. It is more convenient to have one control for frequency and a separate control for I:E ratio. Two new circuits are described which allow this independent adjustment of frequency and I:E ratio.