Ventilators are designed to keep oxygen in the lungs and to remove carbon dioxide. They are an important tool for the treatment of severe COVID-19 cases because the virus can attack cilia in the lungs. If this happens, mucus builds up in the lungs and the risk of secondary infection increases, hindering the absorption of oxygen by the lungs. We are facing many emergencies in this uncertain period of time, not the least of which is the shortage of respirators, as health facilities are collapsing due to the huge number of coronavirus patients. COVID-19 is spreading very quickly all over the world. Because of this high rate of diffusion, many hospital resources are not immediately available. Many industries and companies are building different medical and health devices such as masks, respirators, swabs, medicines, and ventilators in record time. The latter allows people to continue breathing or to breathe better, as the biggest problem of COVID-19 is the blockage of the lungs (Figure 1). In this time of need, technically oriented people have initiated a big open-source project to plan and produce devices aimed at helping patients, including ventilators. The project has involved the participation of hundreds of engineers, medical professionals, and researchers. Many designers use 3D printing and other technologies to create spare parts and equipment on demand.
Figure 1: A professional ventilator (Image: Hamilton Medical)
How do ventilators work?
These devices support breathing by getting oxygen into the lungs and removing carbon dioxide. The oxygen can be controlled through a monitor. The ventilator is connected to the patient through a tube that is placed into the mouth or nose. Modern ventilators are electronically controlled by a small embedded computer. They are classified as life-critical systems, and high precautions must be taken to ensure that they are reliable.
Various ventilator designs, many of which are also present on GitHub, play an important role when hospitals and homes do not have enough devices available. Many ideas involve building low-cost rudimentary ventilators that can aid breathing during an acute lung crisis. However, these are devices that affect people’s medical conditions. For this reason, a doctor should be consulted and random information found on the internet should not be taken into consideration. In fact, there are significant risks with the use of ventilators, especially if they operate at high pressure.
Low-cost open-source ventilator device (PAPR)
This project is available on GitHub (Figure 2). It is a low-cost device that, if properly used, can save many lives. It works at a programmable respiratory rate (10–16 breaths/minute) and can generate a peak airway pressure of up to 45 cmH20, although exceeding 20 cmH20 can be dangerous. It only pushes the atmospheric air (with 21% oxygen). For other oxygenation ratios, professional equipment is needed, but the device is useful and valuable in emergency situations when there is no alternative. The project is still open for changes and suggestions. The creator is available to collaborate with companies and suppliers for mass production of the device. In fact, some components may not be easily available in the short term. The device is still minimal. It would be interesting to design an exhaustive system to minimize viral spread. In fact, it only works in already-infected environments, where there are droplets containing viruses suspended in the air. Operation management is entrusted to Arduino. Systems and solutions should also be studied to prevent the ventilator from becoming dangerous in the event of a power outage.
Figure 2: A ventilator project (Image: GitHub)
The Pandemic Ventilator
This project is available on Instructables and can be made with easily available components (Figure 3). Although it is based entirely on DIY techniques, the aim is to save lives. It can be used as an emergency ventilator. The number of people who will ask for this type of treatment will probably be greater than the current number of existing ventilators. Hospitals cannot buy all the ventilators they need; it would be impossible. This device has a very simple design, but it uses a modern electronic control system. It uses wood, tape, plastic bags, threaded tube, solenoid valves, magnetic switches, and a PLC. The device is continuously updated and improved, both in hardware and software features. The information reported in the project warns that the prototype presented has only an experimental purpose and no safety tests have been carried out. In fact, a ventilator is a potentially dangerous device and must be used only by a trained and certified doctor. Its use, therefore, is carried out under his or her own responsibility. It basically consists of the bellows unit, which is made of wood, valves, and pipes; a PLC controller; some wires and switches; and a power supply. The entire unit is mounted on a piece of plywood measuring 18 × 21 × 0.5 inches. Normally open and normally closed valves are required. They must be of the direct acting solenoid type to operate with air. Threaded fittings with Teflon tape and adapters are also needed. The bellows is made with a large freezer bag.
Figure 3: The Pandemic Ventilator (Image: Instructables)
The valves are connected with pipe and mounted in such a way that the T to the Bellows lines up with the center of the bellows unit. Here, threaded pipe fittings with Teflon are used. The bellows hinge is made of four pieces of 1.5 × 7 × 0.625-in. plywood pieces and a 1.5 × 1.5 × 17-in. piece of wood, two 3-in. hinges. and a 2 × 12.5-in. reinforcement. Figure 4 shows some details of the construction. The bellows is made by screwing down the bottom two plywood pieces to the backing board. The bag is clamped between the two plywood sections during operation using the nuts and washers on the carriage bolts. The magnet is attached to the end of the bellows near the sensor pole, and the sensors are attached to the sensor pole. To make the bag for the bellows, I used a large Ziploc freezer bag. Cut off the zipper part, insert 0.5-in. plastic tubing into the center, and use Tuck Tape to seal and reinforce the edges. The tubing should stick out of the bag far enough to be able to be slipped over the end of the 0.25-in. nipple section of piping. The taped seam of the bellows bag should be on the bottom of the plywood section. Install the hinged cover and then the top 17-in. section. Clamp together with the 4-inch-long 0.25-in. carriage bolts, two nuts, and two washers. The PLC unit is a Direct Logic 06 DO-06DR by Automation Direct. Their units are low-cost, flexible enough, and they have a lot of free software to program with. You could use other PLC units and write your own control program. Besides the PLC, you will also need a 24-V power supply and an on/off switch to start the system. The program is written in Ladder Logic. It basically works as follows:
- It opens Valve 1 and closes Valve 2 until the bellows is full, which is indicated when the top magnetic switch closes.
- It then closes Valve 1, opens Valve 2, and closes Valve 3 so that the bellows can deflate and pump the air to the patient.
- When the bellows drops to the lower limit, the lower magnetic switch closes, and then Valve 2 closes and Valve 1 opens again to refill the bellows.
- A timer lets the patient’s lungs deflate with Valve 3 open. When the timer expires, Valve 2 opens and Valve 3 closes to start the next respiration cycle.
Here is the wiring chart:
- X0 top bellows mag switch
- X1 bottom bellows mag switch
- X2 on/off switch
- C0 24 V
- All returns to ground
- Y0 unused
- Y1 inhale valve (V2)
- Y2 exhale valve (V3)
- Y3 bellows fill valve (V1)
- C0 120-VAC line
- All returns to line neutral
Figure 4: Some details of the construction of the Pandemic Ventilator (Image: TEMPO.CO)
>> Continue reading about additional ventilator design efforts described in the complete article originally published on our sister site, EEWeb.