We are going through an unprecedented situation and unclear when we can enjoy again our good time that we had before this Covid-19 outbreak.
Since the number of infected patients are on rise and there are not enough facilities to meet the need, everyone as an individual or as group, has to play their part.
In purview of lack of ventilators, the cost of procuring it and longer lead time to manufacture it, we explain a simple technique for the SMEs, Volunteering groups, MFG’s or Authorities, how to make a low cost and quick way for a ventilator, especially in this emergency situation and for equipping remote villages.
Demonstration of Prototype/working principle only and all further enhancements, sophistication etc with Developer’s choice.
This is a proof-of-concept mandatory mode pressure-controlled ventilator built around a gasometer. 2 kink valves actuated from a single RC servo control the inspiratory and expiratory circuits. An Arduino Nano controls the servo. This prototype is half scale (approx. 250cm3, 10cmH2O), due to materials at hand: small water trough and a single low-rate aerator. Hoever it shows the basic layout and operation. Briefly, the advantages are that it is inherently safe; can operate from any available air/O2 source with variable FiO2, very transparent operation, and is simple enough to be constructed by any handyman. It can be powered by USB, avoiding dangers with mains power. Humidification is built in!
YELLOW GLOVES – DUMMY LUNGS
Pressure control is safe because no high pressures exist anywhere in the system. If the trough height is chosen to be say 50cm, then even if the gasometer were to jam in the lowest position, insp pressure cannot rise above 50cmH2O, the excess being spilled.
A consequence of pressure control is that it becomes impossible to obtain peak/plateau pressures. But lung compliance and airway constriction could be diagnosed another way. Warning: all the following needs to be vetted by medical people, we are not offering medical advice, only the engineer’s perspective.
If the patient’s lung compliance reduces over time, then the tidal volume at the same set pressure will also reduce. Tidal volume can be read easily from the gasometer: temporarily cut off the air supply at the very start of the insp cycle and observe the fall of the gasometer. This is the tidal volume.
If the patient’s airway becomes more constricted, then it will become necessary to increase the insp time (maintaining the same I/E ratio) in order to achieve the same tidal volume.
The lung/airway may be modelled as a first order system, an RC low pass filter. When volume control is used, this is analogous to applying a step current source input. The output is the voltage, whose curve will look exactly like the usual ventilator pressure curve. However if a step pressure is applied (pressure control), then instead of peak/plateau, you’ll see a spike in current output decaying exponentially. Integrate this to get the charge curve which rises rapidly then approaches a limit, again showing the exponential curve. This charge curve is analogous to the volume observed in the gasometer. Now the rub here is whether or not the lungs/airway may be fairly modelled as a first order system.
Microcontroller – Arduino or…
Valves – Solenoid/kink valves/pinch valves/or
RC Servo – prototype used RC servo, but many other choices
Desideratum, Alarm – not included in this basic system
Water trap/ Filters – not included in this prototype
Again this is engineering view of an effective , low cost, immediate ventilator solution. The one who develops this further should give due diligence and seek the help from a medical doctor. Do you need more details, please contact us.
STAY SAFE STAY HEALTHY