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.
Humidification
·
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.
Control System
·
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.