Saturday, March 28, 2020
Updated Bellows Style Pandemic Ventilator Design – Vinnie 2
I have received a lot of feedback of late on some of my previous designs and I have incorporated them into a revised design of my original bellows style ventilator I named “Vinnie”. The new design incorporates these objectives:
· Must be able to be constructed of components that can be readily sourced during a pandemic where existing supply chains are disrupted and all of the existing components such as sensors and flow meters of sufficient sensitivity and accuracy are not available.
· This lack of sophisticated sensors means that the design itself should be as inherently safe as possible.
· Be able to supply a breathing mixture that is enhanced with oxygen as required
· Be able to control the peak inspiration pressure (PIP).
· Have a method of monitoring the peak inspiration pressure (PIP).
· Be able to control the tidal volume.
· Be able to control the inspiration to expiration ratio. (I:E)
· Be able to control the number of breaths per minute
· Be able to provide Positive End-Expiratory Pressure (PEEP) at different amounts
· Have a filter on the outlet to prevent the spread of infection.
Description of various operations of the schematic drawing:
Basic operation using compressed air only:
· The compressed air is filtered purified air, preferably from a monitored and maintained medical air supply at a hospital or medical facility. If another source of air is used, it must at a minimum come from an oil-free compressor source and be filtered.
· The compressed air regulator reduces the incoming pressure to a lower level.
· The oxygen valve is closed, the water mist injector is closed, the purge valve is closed, the patient inlet valve is closed, and the patient outlet valve is open.
· The compressed air valve opens
· Air fills the bag in the bellows and raises the weight until mag sensor 1 detects that the bellows in inflated to the desired level.
· The compressed air valve is closed, the patient inlet valve opens and the patient outlet valve closes.
· The weight on the bellows drives the air to the patient and the patient's lungs begin to fill. The amount of weight (or volume of water in the container) and the surface area of the bag in contact with the bellows determines the maximum pressure that the bellows can possibly transfer to the lungs and so is an inherently safe design such that this pressure cannot be exceeded. The volume of water in the jug is calibrated before the treatment to provide the desired PIP.
· The increased pressure lowers the water column on the left side of the manometer and raises the water column on the right side of the manometer. The inspiratory pressure can be monitored by observing the difference in height of the right side water column.
· The magnet drops and the magnetic sensor 2 detects the bellows has reached the lower desired setting. The difference in the distance between the two magnetic sensors can be manually adjusted before the treatment in order to achieve the desired tidal volume.
· The patient inlet valve closes and the patient outlet valve opens.
· The patient exhales and the exhaled air is routed through a HEPA filter to prevent the spread of disease organisms into the room air.
· The air drives up the left side of the manometer in the PEEP unit which provides a calibrated amount of backpressure. The air then traverses the bottom and bubbles through the water column to exit. The PEEP can be controlled by changing the volume of water in the PEEP unit.
Adjustment of oxygen ratio
· The oxygen supply can come from a controlled regulated hospital source or from a portable tank.
· The oxygen regulator pressure is adjusted to be the same as the compressed air regulator pressure.
· During the bellows fill phase the control microprocessor will open the compressed air valve for part of the cycle and open the oxygen valve for part of the cycle to adjust the oxygen ratio.
· The microprocessor uses the fill time from the last cycle in order to calculate the proper time percentages.
· The oxygen ratio can be changed at any time during operation as required by controlling an input setting to the microprocessor.
· Whenever there is airflow into the humidifier mixer, the venturi will draw water into the flow stream to mix with the gas stream (oxygen or air). This functions similar to the way a carburetor does in an automobile.
· The spring check valves prevent recirculating flow from the other stream, prevent backflow or air leakage into the water container.
· Since not all the injected water may evaporate into the air stream, there is a purge valve to remove accumulated water.
· The purge valve will open for a short interval at the beginning of every fill cycle to clear any accumulated water in the humidifier mixer chamber.
· The main control unit can be a microprocessor-based system. If no graphical control processor is used then it will need a display and input switches as well. It controls the return to the ground side of the valves.
· A graphical display similar to what is used in a popular commercial ventilator can be used to provide user input control settings to the control processor and provide information on tidal volumes, cycles per minute and I:E ratios.
· A safety microprocessor is to be used to independently monitor all signals to the valves and the mag sensor signals. It will alarm and shut down the power fed to the valves if any timing limits are exceeded or failure of the control processor is detected.
· Due to the mix of NC and NO valves, when the power is off, the patient will default to exhale mode with no pressure applied.
· A safety limit switch prevents the bellows from overinflating. It cuts power to the oxygen valve and compressed air valve when it is activated.
· A mechanical relay prevents both the oxygen valve and the compressed air valve from ever being actuated at the same time.
· A mechanical relay prevents the patient inlet valve from ever being actuated whenever the oxygen valve or the compressed air valve is actuated.
A control system diagram, a valve state table and safety logic table a basic description for assembly and suggested components will be added in the following days.