Sub INR 50,000 VentilatorTeam Lead: Srinivasan Raghavan
Urgent Need: Fluke VT650 Gas Flow Analyzer for two days.
This is an open source design. Developed in collaboration with KAS Technologies and in consultation with Manipal Hospitals for medical consultancy, VASMED for compliance, i2R for design, Hydro Pneo Vac Technologies and VT Vacuum. You are welcome to use it. Stay tuned for our prototype.
Demo for Ventilator Design 1
Full Description for Ventilator Design 1
Demo for Ventilator Design 2
Full Description for Ventilator Design 2
Version T1D2 (10 April 2020)
Version T1D1 details below (01 April 2020)
To create a ventilator or a ventilation mechanism with minimum of electronics that can easily interface with existing hospital infrastructure or hospital like infrastructure for less than Rs. 50,000.
Team has the design 1 (D1) ready and is sourcing components for D2. D1 is a ventilator that can work in pure pressure control mode by providing a pressure pulse. Unlike the Ambu bag designs, it uses a solenoid. D2 will do both pressure control and volume control mode.
- Smaller and cheaper electronics, preferably a PCB for the design provided in our current ppt.
- Pressure regulator that can deliver 0-100 mbar pressure with up to 100 slpm flow rate
- Solenoid with that can flow up to 100 SLPM in ON state and can block up to 4 bar pressure in OFF state with very little pressure loss.
- PEEP or check valve that can be set from 20-60 cm of water column
This is not a certified ventilator. We have put it together as a demonstration of how a simple pressure-controlled ventilator can be assembled in anticipation of a very large demand that India may not be able to cater to. Only time will tell. But then, as they say, hindsight is 20-20.
We are not medical doctors. We are engineers and the information contained in this webpage is based on our understanding on how a ventilator works. We may not be, academically speaking, 100% accurate.
Ventilators and breathing parameters
A piece of equipment that should ASSIST in breathing. Assist is the operative word. A good ventilator determines the requirement of the patient and only provides assistance. This is the most advanced mode of ventilation and is termed “patient-synchronized ventilation.”
The important AVERAGE parameters for ventilation are:
- Number of breaths per minute: Typically 15-20 per minute at rest.
- Inhalation to Exhalation time ratio: Typically 1 second to 1.5-2 seconds.
- Pressure (Critical parameter): 10 cm to 30 cm of H2O column above atmospheric pressure.
- Volume per breath: 500 ml at atmospheric pressure for an average adult
- Volumetric flow rate (important for sizing flow controllers): 30 SLPM (!!)
Not too much pressure: Think of lungs as balloons. If pressurized too much, a balloon bursts. The same will happen to our lungs. Thus, it is extremely critical to not over-pressurize our lungs.
Not too little either: If a balloon loses all its air, it shrivels up. This should not happen to our lungs, as it causes “wounds” and lung trauma.
Pressure Range: Max 40 cm of H2O column during forced inhalation above atmospheric pressure; Min 10 cm of H2O column during forced exhalation above atmospheric pressure. Note: Atmospheric pressure varies from place to place.
This is a very small gauge pressure. We repeat: This is a very small gauge pressure. One should be very careful with pressure control while designing ventilators.
We have already discussed the “patient synchronized” mode in the section above. It requires sensing of various parameters at the patient end and then using PID control to deliver the required volumes of air at a controlled volumetric rate, pressure and frequency.
Pressure mode: In this mode, air is forced into the patient at a certain pressure during inhalation and then withdrawn during exhalation. A pulse of pressure is applied with a certain frequency (the breathing rate). For the electrical engineer, this is a voltage pulse. Given the resistance of the breathing circuit, it forces a volume of air (current) through the patient.
Volume mode: In this mode, a fixed volume of air is forced into the patient in a fixed period of time. The pressure (potential) is raised to permit this flow rate (current).
Both pure pressure and pure volume modes are forced modes that don’t have to depend on patient demand.
Modern ventilators have many-many modes.
Parts of a ventilator
• D1 is a pure Pressure-mode ventilator.
• D2 (yet to come) will include Pressure and Volume modes.
Pros and cons of pressure control
(Source: “Understanding PRVC”, https://youtu.be/j9qbXnAvLsA) .
Pros: Airway pressures are limited, regardless of changes in resistance or compliance, thus preventing damage to alveoli due to shearing forces.
Cons: If the resistance of the lung rises due to disease in the patient’s airway or chest wall, the set pressure limit being the same (or potential being limited) the delivered tidal volume (charge) will fall.
BiPAP, CPAP, the coronavirus and D1
1. BiPAP or Bi level positive airway pressure is essentially the pulse that D1 applies. BiPAP is typically applied through a mask.
2. CPAP is continuous positive airway pressure and is also typically applied through a mask.
3. In both BiPAP and CPAP the exhalation happens into the hospital room. In the case of the coronavirus, this is very dangerous to the medical professionals in the room. MASK-based ventilation should only be used in a negative-pressure room with medical professionals in well-protected suits.
4. D1 is meant for BiPAP but to be administered NOT with a mask. It should be administered using the standard ventilator interface. NO EXHALATION INTO THE ROOM unless precautions as in point 3 above are taken.
Electrical bill of materials
(Medical grade electronics is recommended)
Pneumatic bill of materials
Total cost: Rs. 45,361 for a prototype. Cost expected to significantly come down with volume.
Electrical circuit (to be updated shortly)
Pneumatic circuit (to be updated shortly)
Pneumatic circuit (explained)
(Please read disclaimer: High voltages and pressures are dangerous)
- The electrical circuit (In India) starts with a power supply to convert the 240 V AC supply to a 24 V DC supply that operates solenoid valves.
- The 24 V is supplied through a timing circuit to a solenoid valve to turn it ON-OFF. This determines the breathing rate.
- The pneumatic circuit starts from either the hospital air/oxygen supplies, cylinders or a compressor that could deliver 4 bar pressure. (Atmospheric pressure is 1 bar.)
- These are routed through individual rotameters (flow meters) that allow for fixing the air-oxygen ratio.
- The mixed supply is then regulated down to 40 millibar pressure by a pressure regulator.
- This low-pressure supply is then pulsed to provide inhalation pressure to the patient through the solenoid valve (SV1).
- A pressure-limiting valve ensures that inhalation pressure does not exceed specifications.
- In the ON state of the solenoid valve air is supplied at inhalation pressure. In the OFF state, a bypass supplies air supply at lower exhalation pressure to sweep away exhaled gases. This happens through the orifice.
- The timing circuit is designed such that when SV1 is open, SV2 is closed.
- The PEEP valve ensures that a constant low PEEP pressure prevents the lungs from collapsing during exhalation.
- Adapters that convert from the ¼” world of steel gas piping to the >1″ world of medical plastic tubing are very important.
- System design is crucial to ensure that the conductances in the circuits are kept high to deliver the required flows at the very low pressure drops and provide the doctors with the pressure, volume and volumetric pulses they are used to.
- CeNSE IISc
- KAS Technologies
- Consultations with Manipal Hospitals, HydroPneo and VT Vacuum
Ajay, Akshay, Anirudh, Anisha, Ankit, Harshavardhan, Hira, Justin, Kapil, Maithili, Manjunath, MM Naik, Narayanan, Nishant, Pandian, Prosenjit, Raghuveera, RP, Rohith, Rohith, Sagar, Saurabh, Surendra, Suresh, Sushobhan, Tanushree, Vasu, Vinay, and many more from IISc, PSU, KAS, Manipal, Hydro Pneo and VT Vacuum.