Saturday, March 31, 2007

Putting The Parts Together

I have gotten many of the parts I need to build a prototype for the Pandemic Ventilator. I have two 120V Asco ½” solenoid valves for the inhalation and exhalation valves, and a 120V Burkert ¼” solenoid valve for the bellows fill valve. These valves must be direct acting and not the pilot operated type. They are rated for air as well as water. I got all the pipe fittings needed to connect the valves and other equipment. The magnetic switches are the type usually used for security systems. The PLC unit is a Direct Logic 06 DO-06DR from Automation Direct. I recycled an old control box from another project and I can rewire the switches and lights and buzzer to fit this project.

I tested the bellows unit I made last week to see how long the bag would last. In order to accelerate failure so as to find the weak points I cycled it manually under much higher pressure than it would normally be subjected to. It seems the weak areas are around the tube that is taped in, the taped end, and the edges that rub on the side of the bellows unit. I made some improvements in a second unit by clamping the taped end, allowing more space around the tube for flexing, and removing the sides and end of the bellows unit. It does not need the sides or end to contain the bag once the taped end is clamped into place. The clamp provides physical support to the taped end. I can use the bellows I made before as a lung simulator when I test the control system of the unit.

The plumbing work is done. It just needs the electrical connections made. I hope to be able to test the software for the control unit soon.

Saturday, March 24, 2007

The Bellows Unit is Constructed

I made the bellows unit today. I made it out of scrap wood, a zip-lock bag, some tubing and Tuck Tape. It is not difficult to construct and worked exactly as I envisioned it first try. I tried it out with a can of bolts on the lid for a weight as well. It worked very well and the flow rate is very good from the half-inch tubing. Following are some pictures of the unit. I am actually surprised at how few problems I had getting it to work as I envisioned it. I hope the manometer goes as well. I am going to have to start looking for some solenoid valves and switches now.

Back of Bellows Unit With Curved Edge

Bag Loaded Into Bellows Unit

Bellows With Bag Fully Inflated

Friday, March 23, 2007

Planning the Prototype Build for the Pandemic Ventilator

Now that I have a basic design laid out, I will move on to building a prototype. To aid in planning development I will break the design down into functional sub-units.

I will start on the most complex component to physically build. That is the bellows unit. I will have to do some trial and error to determine the best physical shape. I intend to not have the bag fully inflate and deflate on each cycle so that there will be less fatigue on the plastic. I will have to see about how best to contain the edges of the bag so that it does not get pinched in the moving portion of the bellows.

The manometer is fairly straightforward. The main concerns are getting the optimal tubing lengths and vertical positioning. Possibly I may have to adjust the diameter and length of the tubing at some points of it so that the water is not sucked into the patient circuit.

The rest of the airflow circuit is easy to build. I will use switches to control the valves to bench test the circuit without a PLC unit initially. I will cycle the valves manually with the switches.

Next is to add the PLC and magnetic sensors and get the unit to cycle automatically. Once the system is functioning at a basic level, the alarm software can be added to the PLC and tested. I have only rudimentary PLC programming skills myself, but I know several people that can help me on this.

Next will be the PC control/monitor integration. I have not really thought this far ahead yet. I have a pretty good idea of what I want it to do, but am not sure of the best approach to achieve it. I will take pictures and video of each step and post them. Hopefully by the time I am able to demonstrate a basic system functioning, I will have a programmer interested in doing the PC portion of it.

Tuesday, March 20, 2007

Preliminary Layout for Open Source Pandemic Ventilator Design PDV1 070319

For some reason this picture came out blurry when I uploaded it. You can get a clearer version if you copy it or double click on the image. CC creative commons licence at bottom of page.

Description of Preliminary Layout for Open Source Pandemic Ventilator Design PDV1 070319

The design consists of a pressure regulator, 3 valves, a bellows unit, a manometer pressure sensor unit, some switches and alarms, a PLC and a PC.

This design is optimized to be able to be built with readily available components. Other than the tubing that connects to the patient, (which would be sterilized and reused) none of the components are specifically “medical parts”. It is expected that supplies of components specifically designed for medical devices will be in very short supply in a pandemic situation, and would not be available. Later on I will try a version using a commercial pressure sensor instead of the manometer system described. This will allow greater control flexibility of the device. The design philosophy is such that the physical components can be constructed fairly easily. All the parts are commodity items and easily available (you could steal em from factories if you had to) even if all production and supply ceases in the pandemic. The software design for the PLC and PC will be more complex, but will be freely available as open source including source code.

The Pandemic Ventilator is designed to meet AARC guidelines for Acquisition of Ventilators to Meet Demands for Pandemic Flu for alarms and for ease of use. I have not yet added humidification, oxygen concentration control or PEEP to this design but these additions will probably not affect the final design too much. In concept it is a system that essentially takes something similar to an ambu-bag manual ventilator and adds enough automation and safety control systems to bring it up to the AARC acquisition guidelines.

Description of Components (see drawing)
  • A bellows unit is constructed from plywood or sheet plastic using a standard door hinge at one end. More exact plans for the bellows will be published once I build the first prototype.
  • A plastic bag (possibly a drainage bag) is placed in the lower portion of the cylinder, with the opening of the bag connected to the system tubing with Tuck tape. The bag supplies the sealing properties for the bellows, and may have to be changed on a regular basis if it wears out.
  • The bellows will have a magnet attached at the top to activate the position sensors.
  • MS1 and MS2 are magnetically activated sensors (either Hall effect or magnetic switch) that sense when the piston has reached the top and bottom of its travel. MS2 is a fixed sensor, and MS1 can be adjusted to allow for adjustments in volume per cycle.
  • A weight is placed on the top of the bellows in order to allow the bag to deflate and push air into the patient’s lungs during the inspiration phase. The amount of weight on the bellows divided by the area in contact with the bag determines the maximum pressure that can be developed.
  • V1(NC), V2(NC), and V3(NO) are ¾” or ½” solenoid valves (or similar).
  • The manometer is a U shaped tube filled with water. It’s height in relation to the measuring point and the length of vertical tubing are adjusted in order to be able to measure the limit maximum and minimum pressures expected. A magnet is inserted into some foam in order to make it float at the water surface. The water level limits (which indicates the pressure limits) is monitored by magnetic sensors clipped to the outside of the tubing. The pressures can also be marked on the tubing so that the operator can have a visual indication of the maximum pressure achieved. I will publish more exact specifications as to the height and length of the tubing once I build and test the prototype.
  • An outlet filter is connected to the exhalation line in order to prevent infection of staff with flu virus.
  • Interconnections are with standard plastic pipe and flex hosing with gear clamps.
  • The PLC should have a minimum of 7 inputs and 5 outputs. The PLC should also have a communications port (RS232) in order to communicate with the PC. Software to operate various popular brands of PLC will be developed and made freely available. Various controls and alarms are connected directly to the PLC.

Description of PLC Control Algorithm (see drawing)
(Starting from the pressurized air source)
  • The pressure regulator reduces the supply pressure to a reasonable working pressure
  • The PLC opens V1 and closes V2. V3 is open to let the patient exhale.
  • Air enters the bellows and raises the piston. The PLC will sense MS2 opening and begin a timer. If the allowable window of time interval between MS2 opening and MS1 closing is not achieved, a malfunction alarm is generated, stopping the cycle.
  • When the magnet reaches MS1, V1 closes.
  • When the low pressure limit of the manometer is triggered or enough time has elapsed since the last cycle based on the selected inhalation to exhalation ratio or set time, V2 opens and V3 closes to inflate the patient’s lungs. The pressure limit points on the manometer are monitored by the PLC. If the pressure rises too high, an overpressure alarm is generated and V2 is closed and V3 is opened to protect the patient from overpressure.
  • The piston begins to drop and MS1 is opened. The PLC starts a timer. If the time interval between MS1 opening and MS2 closing is too short a line disconnection alarm is generated. If the time interval is too long, an obstruction alarm is generated. When the piston drops and MS2 is closed again, V1 opens, V2 closes and V3 opens to allow the patient to exhale again.
  • The PLC also monitors the cycle rate over time and generates an alarm if the selected control parameters are exceeded.
  • The PLC generates audible and visual alarms as required. Audible alarms can be set to sound different for different alarm conditions. The Stop, Mute and Reset/Resume keys allow for control of the ventilator.

Description of PC function (see drawing)
  • The PC is connected to the PLC via an RS232 connection. This connection transfers status data from the PLC to the PC and also allows the PC to input set points and controls. The PLC does not absolutely require the PC to maintain operation, but will generate an audible alarm if the communication is interrupted.
  • The PC will have visual interface software that mimics popular existing ventilators in appearance and operation. Non supported operations will be crossed out on the interface. This allows for easier retraining and higher comfort levels among operators of the equipment. The supported equipment type is selected when the software is installed.
  • The relevant operating and alarm parameters are entered into the PC and they are transferred to the PLC registers.
  • The PC can also perform diagnostics on the operation of the PLC in order to enhance total safety. The PC can also generate it’s own visual and audible alarms.
  • The UPS generates an alarm at power failure and supplies backup power as well. If the PC is a laptop with a battery, it will also be able to supply power failure alarms.

Still to be done
Oxygen, Humidification, PEEP design
Build and test a prototype with PLC only.
Add PC control functionality

I could use some help, so far it’s me, my son, and some friends at work (in dialysis) developing this.

Please be patient if I do not have all the terminology right, and comment or email tell me if I am making some drastic mistakes or you have some insight that would let me make this thing much better. I knew almost nothing about ventilators three weeks ago

Sunday, March 18, 2007

Being Aware of the Shortage

The need for more ventilators for pandemic planning is quite obvious, but, given the fact that most large organizations respond to events rather than proactively plan, and they are always worried about appearances. Letters to public media to investigate will probably have more effect than individual letters to hospitals, as media sources are far more difficult to ignore.

The questions to ask of your hospital or local planning organization are:
1. Are you aware of the need to plan for a pandemic?
2. Do you have plans in place to deal with the expected surge?
3. Do you think the existing plans will be sufficient or do you need more support in place?

I hope to have a preliminary design posted soon.
If you think this is an important issue, please send this website address to your friends and click on the Digg button.


Wednesday, March 14, 2007

The Cost of Providing a Ventilator Safety Net for a Pandemic (And the Cost of Not)

The Cost of Providing a Ventilator Safety Net for a Pandemic
(And the Cost of Not)

Today I am talking strictly money. This does not men I do not appreciate the extreme suffering that many avoidable deaths will have on the fabric of our (caring?) western civilization. I just want to put the numbers in focus.

Donald McNeil ( of the New York Times, in his column of March 12, 2006, "Hospitals Short on Ventilators if Bird Flu Hits" says that it would cost the US 18 billion dollars to buy enough ventilators to prepare the US against a pandemic similar to the 1918 Spanish Flu. I think this number is way too high. Numbers like this scare the government so much that they buy almost no ventilators at all. They give up.

$18,000,000,000 dollars will buy 600,000 ventilators at $30,000 dollars each. Since there are only about 100,000 ventilators currently in the US, the existing physicians, respiratory therapists and RN staff would have to be able to expand their workload by a factor of 6. This, also in the face of many of their own number being sick. I think a more reasonable number would be that they could expand their capacity by a factor of 3.

McNeil obviously bases his estimate on the figure quoted by the US government that 750,000 would require ventilators in a pandemic. The 750,000 would not all show up at the hospital the same day. Pandemics can take as long as 12 to 18 months from start to finish. They can come in several waves, so that each ventilator can be used to treat several patients sequentially. 200,000 ventilators is a more reasonable maximum. The ventilators need not be the most expensive fully featured units either. If you could get 200,000 ventilators for $5,000 each, the cost would be only 1 billion. That’s less than a penny a day for each US resident over the next year.

Now a very high proportion of the deaths will occur in younger people. These are the people that are supposed to be paying for the huge national debt and social security obligations of the older people. How many trillions of dollars in lost future tax revenue does this represent.

In the US, they are planning on 5,000 to 10,000 spare ventilators, depending on whose numbers you believe. In Canada there are no plans to stockpile additional ventilators. Thank You Mr. Harper.

Monday, March 12, 2007

Below is a reworking of my original proposal. I added some references and some calculations of the number ventilators required in a pandemic.
See Preliminary Layout for Open Source Pandemic Ventilator Design PDV1 070319

I am also having an ongoing discussion of this topic at
If you want to hear what others think or submit your own ideas, go over and have a look.

Sunday, March 11, 2007

A Proposal for an Open Source Design to Assemble Ventilators to Meet Pandemic Surge Demand

Clarence Graansma

In a predicted pandemic influenza outbreak, it is expected that there will be a severe shortage of ventilators. Ventilators are expensive to buy and maintain, so government organizations are stockpiling only a minimal reserve. Manual type ventilators will not be adequate for many cases. The solution to this problem may an open source design for an automated ventilator that will be adequate for the perceived need, and can be built from parts that will be available in sufficient quantities during a pandemic. A community of developers must design, and test a ventilator, and make the design freely available for individuals and healthcare organizations to build their own units in a pandemic crisis.

It is expected that in a pandemic influenza outbreak the number of people requiring a ventilator will be much greater than the number of ventilators that are available in hospitals. There are approximately 105,000 mechanical ventilators and 60,000 intensive care unit (ICU) beds in the United States. This is only 1 ventilator for every 2600 people and 1 ICU bed for every 4500 individuals. In an avian flu pandemic, it is estimated that 30% of individuals will become symptomatic and up to 50% will require ventilatory support. Using more conservative estimates, data from the H1N1 pandemic flu of 1918 suggested that 2% of people required ventilatory support. If the same is true for H5N1 (although less than what is currently estimated), a city of 1 million people will have 300,000 affected individuals and 6000 of whom will require a ventilator .

Based on these numbers, a city of 1 million people would have 385 ventilators in its hospitals. Since 80% to 100% of the stock of existing ventilators is typically already being used in the ICU units , this leaves at most only 77 ventilators available at any given time. Triage methods will be used to remove some of the people already on ventilators in order to give to people requiring ventilatory support due to the pandemic. Now it is possible that the impact of the pandemic may be considerably less than the 1918 event due to the use of vaccines and anti-viral medications. Let us assume again a very good response to medications, and we reduce the number of people requiring ventilatory support by 50%. The expected patient load would now be 3000. Pandemics do not always strike all at once, but may come in several waves such as the 1918 pandemic . The same ventilator could be used sequentially 2 or 3 times in each wave to treat pandemic victims in perhaps 3 subsequent waves. This means that each ventilator could now be used to treat 6 to 9 people. Assume we made up to 200 ventilators available via triage by removing existing chronic and elderly patients from ventilatory support and then used each of these ventilators to save 8 people from the pandemic. This would save 1600 of our 3000 patients.

It is obvious that even strict triage and with conservative assumptions of severity, we will be short of ventilators. Even if we had an unlimited supply of ventilators, we will not save everyone. Many will die even with a ventilator and good critical care. If the availability of ventilators were not the issue, the limiting factor then would be how far we can extend our critical care support system. Physicians, intensive care nurses and respiratory therapists will also be affected by the pandemic and their ability to respond may be reduced. There are also issues of availability of other supplies. A reasonable assumption of the limits of support extension would be between a factor of 2 to maybe 3. This means our city of 1 million would need to have available between 385 to 770 additional ventilators. Now these ventilators need not have every possible alarm and treatment option, but they must have enough automation so that nurses and respiratory therapists (RTs) can run them without constant intervention.

Some hospitals and organizations are stockpiling manual ventilators for such an emergency. These are either bag type manually operated ventilators, or pressure driven transport type ventilators with no alarm systems . These have the advantage of low cost, disposability and no maintenance. These devices require extensive supervision by qualified personnel, however and will not be adequate in this situation. They may be useful if appropriate automation and alarm systems could be fitted. To buy enough full function ventilators to fulfill the need is too expensive for hospitals to consider. Even if the government were to pay for enough ventilators to supply the entire country, there would not be enough centralized manufacturing capability to supply the product when it is needed. Neyman and Irvin have published an innovative method to put up to 4 patients on a single ventilator. This system requires further testing and would not have very good monitoring ability.

Proposed solution:
From the previous sections it is obvious that what is required is a reference design for a low cost, relatively reliable ventilator that can be produced in a large quantity in a relatively short time from commonly available materials that are not in short supply. The device will not require every feature and ability of existing full function ventilators, but must have the features required to properly care for Acute Respiratory Distress Syndrome (ARDS) in a pandemic situation. The device should be automated as much as possible as to enable the existing RTs to care for a large number of patients. Also the design of controls and alarms should be intuitive so that other persons can be trained to help support the devices in use. The components used to build these devices must be components that will be available during a pandemic.

The best way to engineer and distribute such a reference design would probably be based on an open source model. Existing projects to emulate and gain organizational insight could be the "One Laptop per Child" project or the various open source software projects such as the Mozilla Foundation or various Linux branches. The non-profit Architecture for Humanity ( is doing a similar thing for designs for housing to rebuild communities in the wake of natural disasters. We need to start a Pandemic Ventilator Project now.

The ventilator must be able to be built from commonly available components sourced from the industrial and instrumentation marketplace. The component specification should be standardized as much as possible. For example a good specification would be "12V solenoid actuated air valve with a minimum flow rate of 3 liters per minute" rather than "ACME solenoid valve AS3506T." This will allow substitution if required.

A centralized listing would be have to be established and maintained of possible components that will satisfy the requirements and known supply sources. The design should incorporate "fail-safe" design techniques as much as possible. In order to use "off the shelf" components, the design will have to rely on an electronic control system to enhance safety and usability instead of using innovative pneumatic component designs. It will probably be either PLC based or some type of dedicated PC control.

Testing criteria and minimum performance specifications will have to be developed.
It is expected that alpha, beta and release candidate versions will be released and then tested. There may be version upgrades based on testing results. It may be beneficial to fork the project at some point in order utilize differing design philosophies or to produce devices tailored to certain requirements, such as simplicity of operation, desired features or ease of assembly.

A community of developers will need to be established. It is doubtful that existing ventilator manufacturers will participate on a formal level due to competitive and legal obstacles, however it is expected that they may allow some of their engineering staff to participate on their own as a humanitarian gesture. It would be expected that professional groups may encourage their members to support the project. It would be very helpful to obtain the support of university engineering labs. It is expected that the bulk of support would be individuals from the medical, instrumentation and information technology communities.

A legal framework will have to be established to protect contributors to the project from legal liability of any misuse of the reference design or any lawsuits from failure of a device. Something like the GPL will have to be used to control derivative use of the reference design. As it is unlikely that the design will be submitted for FDA approval, there would have to be legislation enacted by governments in a crises to permit use of any devices produced. Perhaps some draft documentation to guide the government agencies at the time of a crisis could be produced ahead of time. Humanitarian groups may wish to use the designs for third world relief projects.

A foundation may have to be established to support the project. A core group will have to be established to control and maintain the direction of the project. Training, servicing and operation guidelines and materials must also be produced and maintained. A website for feedback, communication and software distribution will be required. Perhaps Sourceforge could be used.

Mar 11 2007


1 Disaster Medicine: Understanding the Threat and Minimizing the Effects
Christopher J. Lettieri, MD
Medscape Emergency Medicine. 2006;1(1) ©2006 Medscape
Posted 05/31/2006

2 CMAJ • November 21, 2006 • 175(11) | 1377
Christian, Michael D. et al

3 Mass Critical Care with Scarce Resources: A Community Planning Guide AHRQ Publication No. 07-0001 Marc Roberts PHD et al

4 Taubenberger JK, Morens DM. 1918 influenza: the mother of all pandemics. Emerg Infect Dis [serial on the Internet]. 2006 Jan [date cited]. Available from

Volume 4, Number 4, 2006
The Prospect of Using Alternative Medical Care
Facilities in an Influenza Pandemic

6 A Single Ventilator for Multiple Simulated Patients to Meet Disaster Surge
Greg Neyman, MD, Charlene Babcock Irvin, MD