Intermittent Positive Pressure Breathing Device

Abstract

A ventilator implemented completely with fluidic devices provides independent control of inhalation time, exhalation time and breathing gas flow rate. The basic fluidic system comprises a low frequency oscillator which in the form of a flip flop is controlled in its two stable states by means of independently controlled time delay relays. The output of the flip flop is amplified by a digital amplifier and operates an on-off valve which is used to direct breathing gas from the source to the patient. Independent control of the flow rate of the breathing gas is by means of a needle valve. With this basic fluidic system, there are seven other features of the apparatus. One is a maximum pressure control which on inhalation is responsive to the patient's breathing air pressure. The second feature is a sensitivity control, which during exhalation is responsive to the patient inspiratory effort. The third feature is a positive end exhalation pressure control. The fourth is an intermittent mandatory ventilation control which permits breathing rates as low as one breath per minute. The fifth feature is a manual control which allows the termination of the exhalation phase and initiation of the inhalation phase manually. The sixth feature is a sensor which is responsive to the breathing gas pressure at the patient. If the apparatus becomes detached from the patient, pressure cycling is modified and an alarm system sensitive to this pressure is activated. The seventh feature is a safety valve which allows the patient to breathe atmospheric air when the supply pressure of the source gas fails.