Control System
Key case-specific parameters to be set by the operator are the level of negative pressure (to compensate for variable stiffness due to inflammation or other conditions); the duration of negative pressure (inhale duration); and the cycle time (inhale plus exhale plus ramp times; breathing rate). A wide variety of approaches are possible, depending on available resources.
An adjustable relief valve (Fig. 6) could provide patient-specific pressure control. Timing of valve opening to negative and neutral pressure could be controlled mechanically via rotary motion (e.g. adjustable cam and follower; rotating disk with holes, possibly powered by air flow) or electronically (e.g. Arduino with solenoid valves).
In extremis, multiple patients could be ventilated quickly using a shared, manually operated system until an automated solution can be arranged.
Fig. 6: A flap with an adjustable weight (shown here as a bolt with a variable number of washers) will remain closed (upper) while the force due to the pressure differential (white arrow) is less than the force of gravity (black arrow), and will open (lower) if the pressure exceeds the set point. A spring with adjustable preload could also be substituted here.