CPAPs RE-INVENTed into Emergency Ventilators Using PLCs and HMIs

CPAPs RE-INVENTed into Emergency Ventilators Using PLCs and HMIs
CPAPs RE-INVENTed into Emergency Ventilators Using PLCs and HMIs
With the COVID-19 pandemic disrupting life as we know it throughout the world, health care facilities not only faced the grueling challenge of caring for an influx of virus-affected patients, but also contended with projected shortages of necessary life-saving supplies. The ventilator—a machine providing respiration for patients unable to breathe on their own—has one of the highest media profiles of potentially scarce medical devices.
In an attempt to curb supply shortages, various organizations called on developers to build “emergency ventilators” with varying specifications. One such call was issued by the U.S. Air Force for the design of an emergency ventilator—using readily-available, commercial off-the-shelf (COTS) components to avoid interference with medical supply chains.
A team at Auburn University’s Samuel Ginn College of Engineering responded with the RE-INVENT emergency ventilator, representing American innovation at its finest in a time of need. Several emergency ventilator creations have popped up recently, but some are unable to provide warm, moisturized air to help a patient breathe while utilizing proven hardware for the reliability required in life-critical applications. RE-INVENT does both, with an assist from AutomationDirect components.

Planting the Seed

The narrative began when engineer Ryan Hill at Integrated Solutions for Systems (IS4S) caught wind of the Air Force “Hack-a-Vent” challenge, calling for the use of COTS parts totaling $300 or less to build an emergency ventilator. As a former Auburn engineering student, Hill approached Dr. Zabala at the Samuel Ginn College of Engineering with the thought that IS4S could manufacture ventilators if provided a proper design. Zabala shared the information with Dr. Burch and Joe Reagan, and they began working on rudimentary concepts to fulfill the Hack-a-Vent requirements.
However, the team soon shifted away from their early ideas, as it did not seem possible to build a practical ventilator at the required components cost of $300. They were more interested in creating a device for reliable application alongside medical staff in the emergency room. Hack-a-Vent spurred development into motion, but the engineers ultimately abandoned some of the challenge’s constraints in order to build a purposeful device able to provide life-support when called upon. Functionality and robustness became the primary design objectives, while keeping the price-point at a reasonable level.

Iterating Through the Generations – in Hyperspeed

A team member was already personally familiar with using continuous positive airway pressure (CPAP) machines, and figured a standalone CPAP could be used as a temporary breathing aid for COVID-19 patients in the absence of a ventilator. The two devices perform a similar primary function, with the ventilator adding pressure control for inhalation (inspiration) and exhalation (expiration). If the CPAP—available in larger quantities and at cheaper cost than a ventilator—could be modified to take over respiration for the affected patient, it could operate as a ventilator.
By itself, a medical-grade CPAP provides warm, moisturized air to the lungs, but the team needed a robust, reliable method to control air pressure to induce inspiration and expiration. They established a setup with two electrically-actuated valves for breathing control and an additional valve to blend additional oxygen with the air. Dr. Burch was able to acquire solenoid valves from maintenance personnel at the university for initial prototyping. For this first-generation, he enlisted the help of his son to create a simple integrated circuit to control the valve operation and timing cycling between inspiration and expiration phases (Figure 1).

Figure 1: For early-generation CPAP-based ventilator designs, the team prototyped with basic and readily available parts.
With its promising results, the first-generation device gave the team confidence to continue design. Though effective for testing the initial concept, the integrated circuit was cumbersome to adjust, and the engineers needed to be able to modify the inspiration to expiration (I/E) ratio. To speed development efforts and enable rapid testing and adjustment, the developers introduced a programmable Arduino prototype board to replace the integrated circuit. This second-generation configuration gave the team the tools it needed to greatly refine the mechanical, electrical, and controls components of the system, but it still lacked the reliability necessary to function in a life-critical capacity.
At this point in development, Dr. Burch enlisted the expertise of his friend Jim Chapman, an industry controls engineer. Chapman quickly specified the use of the AutomationDirect CLICK programmable logic controller (PLC) to replace the prototype board (Figure 2). This commercially available PLC would make it easy to program and modify the configuration, while delivering the reliability and robustness demanded by the application. This third-generation device formed the basic automation architecture for RE-INVENT.

Figure 2: The readily available and economical AutomationDirect CLICK PLC made it easy to develop the ventilator, and delivered the reliability needed for such an application.
With the further addition of an AutomationDirect C-More human-machine interface (HMI), users could better interact with the automation, so making adjustments to settings like the I/E ratio during testing became even simpler.
Development up to this point transpired of a matter of days, literally over a weekend. Such results represented a turbo-charged pace compared to the rate at which most machines—let alone medical devices—are developed.

Prototype Board vs PLC

There have been other recently-produced “emergency ventilators” using prototype controller boards like the Arduino, and it would be reasonable to wonder why the Auburn team replaced their Arduino with a PLC. Prototype boards are perfect for education and proof-of-concept: they are quick to procure, cost-effective, easy to program and modify, and ready for I/O out of the box. However, they are commonly mistaken to be suitable for all applications. For critical applications, however, the hardware and software simply do not offer the needed reliability.
PLCs, from a hardware standpoint, are built to withstand large variations in temperature, high-vibration, and other harsh environmental factors. As far as software goes, PLCs run real-time operating systems (RTOSs) that execute all logic and scan inputs and outputs hundreds of times per second. AutomationDirect CLICK PLCs provide cost-effectiveness and ease of configuration in addition to the robust hardware and RTOS qualities of PLCs.
Prototype boards, by comparison, are not manufactured to endure harsh environments. From a software-standpoint, they operate primarily as cyclic execution systems, requiring received or output commands to fully complete prior to moving to the next line of logic. While there may be workarounds to reduce the risk of these systems “hanging” in the event of an error, these factors make prototype boards unfit for use in critical systems.

Design Details

Auburn University’s RE-INVENT integrates an unmodified CPAP machine with the following elements:
  • Oxygen-blending valve
  • Actuated valves
  • Viral filter
  • Hoses
  • Pressure transmitter
  • AutomationDirect CLICK PLC
  • AutomationDirect C-More HMI
The team sourced many of the COTS automation components through AutomationDirect. Excluding the CPAP machine, each RE-INVENT unit utilizes about $950 worth of parts, coming in well over the Hack-a-Vent’s constraint but still a very reasonable cost (Figure 3).

Figure 3: Excluding the CPAP machine itself, the RE-INVENT ventilator assembly is configured from less than $1,000 of commercial off-the-shelf parts.
When Chapman came on board, he quickly specified the AutomationDirect CLICK PLC and C-More HMI as the perfect candidates for RE-INVENT, citing their ease of use and reliability. For many years he had used CLICK PLCs under harsh environmental circumstances without failure, so had no hesitation recommending their use in a life-critical application. Additionally, their ready availability, quick procurement, and reasonable cost made it an easy choice for the application’s PLC.
Chapman used the AutomationDirect free PLC software to program the control logic and the low-cost HMI software to configure the user interface. In Chapman’s experience, the AutomationDirect products are also effective as a teaching tool because the new programmers can immediately begin creating ladder logic without user-interface distraction or an excess of prerequisites to configure.
In addition to the PLC and HMI, the Auburn team purchased power supplies, circuit breakers, zero-cross relays, terminal blocks, DIN rail, wire, and cables directly from AutomationDirect. AutomationDirect also provided world-class customer service and technical support, and worked with Auburn throughout the project to help ensure success on the automation and controls side of the application.
With a project lifecycle which included quality control, prototyping, planning, and development, the team created a system ready for use in the emergency room.
The operation of RE-INVENT is designed to be easily understood by medical staff familiar with CPAP machines and ventilators (Figure 4). The technician begins by turning on the CPAP and configuring all initial settings on the CPAP machine itself. On the separate box containing the added components, the technician enters the I/E ratio and breaths per minute rates on the touchscreen HMI. The system will alert medical personnel via an on-screen alarm in the event of high or low differential pressure between inspiration and expiration phases as sensed by the 4-20mA, 0-20” H2O pressure transmitter.

Figure 4: The RE-INVENT ventilator is designed for easy operation and configuration by medical staff.

What Lies Ahead

After rigorous testing and measurement with a simulated lung apparatus, it was time for the RE-INVENT’s first real-life trial. The engineering team partnered with Auburn University’s College of Veterinary Medicine to test the machine on a 200lb, anesthetized male Boer goat. With the CPAP set to a pressure of 20cm H2O, the test team varied the I/E ratio, breaths per minute, and oxygen supply levels. Veterinarians monitored the goat’s arterial blood gases, which remained within normal reference ranges throughout the test. At the test’s conclusion, the goat regained consciousness as expected and was verified to be healthy and fit.
At the time of writing, there is still some testing to be done in order to more accurately capture the maximum and minimum pressures during operation, which is a difficult task considering the low pressures and high breaths per minute rates. In the meantime, Auburn University has assembled 12 RE-INVENT machines, and IS4S has built an additional 89. The flagship machine will remain in the lab at the engineering college for further testing and software refinement—code updates are easily applied to field units as the PLC control logic is improved.
Auburn University estimates that hundreds, and perhaps a few thousand, of these devices can be assembled without a large strain on supply chains, although it would not be possible to obtain components for tens of thousands. Finding parts is not without its challenges, as it is difficult to find sufficient oxygen-rated valves in a short time-span. It is important to note, however, that production of RE-INVENT avoids interrupting the supply chains of classic ventilator components. In the meantime, hospitals have requested deliveries of the machine. Auburn University and IS4S are seeking appropriate approvals for deployment.

Ready to Answer the Call

Tough times put people to the test. The team at Auburn University’s Samuel Ginn College of Engineering rapidly responded to the pandemic situation, putting their skills into action to help address a global need (Figure 5). Though the time to develop RE-INVENT was short, the undertaking demonstrates how resourcefulness and the use of commercially available components can play a key role in product development to successfully address a need.

Figure 5: Dr. Michael Zabala (at left) and Dr. Thomas Burch (at right) demonstrate the RE-INVENT, which is built from commercial off-the-shelf parts to adapt a common CPAP machine into a ventilator.
For such a critical project—patient’s lives depend on this machine—the importance of specifying robust, reliable components cannot be understated. AutomationDirect helped the team supply large quantities of reliable automation components in a short span of time, delivering products ready for development right out-of-the-box. Should circumstances require it, RE-INVENT is ready to save lives.

About The Author

Dr. Tom Burch received his BSME and MSME degrees in Mechanical Engineering from Auburn University and after completion of his PhD from Louisiana State University he returned to Auburn and began his teaching career in 1992. He is currently a Senior Lecturer in the department of Mechanical Engineering. He has also been a principal in the Boiler Efficiency Institute (BEI) since 1990. His consulting work in energy conservation and usage has spanned four decades, three continents and eight countries. During this time he has delivered hundreds of workshops and seminars on energy related topics and consulted with numerous industries, institutions, and government agencies. He is a registered Professional Engineer in the state of Alabama.

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