The design has an I:E ratio which is fixed by the internal synchronous rotary valve slots as 1:2 (this can be changed with a swap-out of the valve sleeve), and additionally allows for full control of
1. Exact tidal volume and compression ratio setting (350-800ml Vt)
2. Vt pressure curve phase and dwell angle mechanical control
3. Buffered PEEP control (PEEP valve with additional air flow supplemented by a secondary piston to ensure expiration pressure doesn’t return to zero unless machine is stopped for a short period of time >2s)
4. Y-ventilator breathing circuit connections with separate inspiration and expiration ports and valve connectivity.
In addition to this, the incorporation of these design features to allow for simple set-up of a patient and safe operation by medical/volunteer staff
1. Standard sizes throughout for all ports, for fitting of biological filters or hoses to safely vent away expired air and aerosolized exudate from the patient
2. Ventilator system is very compact and light, target design weight is less than 1KG and this may be mounted on whatever format is available – chair, trolley, bedside or custom framing.
3. System is made entirely from 3D printed (MJF) or injection molded plastic parts.
4. Silicone balloons or bellows as a compressor are not used. These are complex to make/source and will fail when used for long periods of time or thousands of cycles – a manually actuated all-plastic reciprocating non-cylindrical compressor is employed giving fine control of Vt and pressure over hundreds of thousands of cycles.
There are two main aspects to the ventilator core – two individually controllable synchronous rotary valves, operated on 1:2 I:R ratio which provide adjustable dwell angle between inspiration and expiration strokes. A reciprocating piston compressor provides pressure for inspiration, but also a secondary piston provides buffering back-pressure for PEEP. Tidal volume is set by a pin in the crank, moving the crank conrod closer or further from the crank wheel, and adjusting the volumetric sweep of the piston. Pressure is set by a relief valve on the inspiration circuit, limiting the maximum allowable pressure on the inspiration pump. PEEP is set by a valve at the output of the synchronous rotary valve expiration circuit. There are two configurations for the PEEP valve being currently considered, a sprung one-way back-pressure valve, and a settable weight-based pressure relief port. The unit is geared such that a user will crank two revolutions per full breathing cycle.
Each inspiration and expiration circuit is isolated and closed, controlled by the synchronous rotary valve, so that no expired air can be re-breathed by a patient. It is set up to use a Y-configuration of the ventilator circuit, ensuring fresh air and isolation of each breathing cycle. In this way, it is possible to add biological filters, also addition of oxygen to the inspired breath.
Pressure and flow monitoring
External manometers provide individual pressure readings for inspired and expired air while the unit is in operation. Flow monitoring with an external spirometer may also be employed – these are simple components that may be added to the ventilator circuit, and are not shown in the design renders.
Vt = 350-800 ml
IP = 10-40 cm H2O
PEEP = 0-10 cm H2O
Rrate = 4-20 rpm (max – manually determined)