RapidAlarm: Hearing aid algorithm is secret ingredient in low-cost emergency ventilator monitoring system
A hearing aid algorithm is the key behind the Illinois RapidAlarm, a new open-source sensor and alarm system that makes emergency ventilators, such as the Illinois RapidVent, more useful during the COVID-19 crisis. It uses low-cost, widely-available parts so that it can be produced quickly and inexpensively to help address shortages.
The Illinois RapidAlarm, unveiled in April 2020, attaches to existing pressure-cycled ventilators and uses a pressure sensor to estimate clinically useful metrics such as pressure and respiratory rate and sound an alarm when the ventilator malfunctions.
“Many of the emergency ventilators being produced for COVID-19, including the Illinois RapidVent, lack the monitoring capabilities of more expensive commercial ventilators, so clinicians have to constantly monitor patients using them to make sure they are still breathing,” explained Ryan Michael Corey, an Illinois ECE post-doctoral research fellow.
The Illinois RapidAlarm team was led by Illinois ECE professor Andrew Carl Singer, Fox Family Professor of Electrical and Computer Engineering and Associate Dean for Innovation and Entrepreneurship in The Grainger College of Engineering. The engineering team also included Illinois ECE professor Michael L Oelze, Illinois ECE post-doctoral research fellow Ryan Corey, and Illinois ECE graduate students Evan Michael Widloski and David Null. They worked with local pressure-monitoring experts from Creative Thermal Solutions, Inc., design specialists from the Siebel Center for Design, and clinicians from Carle Health.
The team’s newly released paper describes how the Illinois RapidAlarm works. The algorithm was developed by Dr. Corey and inspired by a hearing aid algorithm called dynamic range compression, which he studied as part of his Illinois ECE doctoral dissertation on listening technology. Compression helps hearing aids respond to changing sound levels by making quiet sounds louder and loud sounds quieter. To do so, it must track the loudness of sound signals over time. The ventilator monitoring system uses a similar tracking algorithm on the pressure signal measured in the patient airway. When the highest and lowest levels of the pressure signal are far apart, the ventilator is working correctly. If those levels get too close together, there might be a malfunction, such as a loose tube.
“We wanted the monitoring system to run on a low-power, low-cost microcontroller, so the signal processing algorithm had to be extremely efficient. Hearing aids also have severe power constraints, so the dynamic range compression envelope tracking algorithm was a perfect fit,” said Dr. Corey.
“The Illinois RapidAlarm measures the pressure in the airway 100 times per second, but we only need to do a few calculations on each measurement, so the algorithm can run on virtually any low-power microcontroller,” explained Mr. Widloski, who worked on the circuit board design and firmware code for the project. “The design is simple enough that anyone with a soldering iron can assemble one of these units in a few minutes.”
The Illinois RapidAlarm was designed to complement the Illinois RapidVent. In March, the Grainger College of Engineering launched the Illinois RapidVent project to design an emergency ventilator that could be rapidly and inexpensively produced. In little more than a week, the team built a functional pressure-cycled pneumatic ventilator, which is now being manufactured by Belkin. The Illinois RapidVent is so easy to produce in part because it has no electronic components. However, it lacks many of the monitoring features found in advanced commercial ventilators. The Illinois RapidAlarm adds these monitoring features.
Illinois RapidAlarm attaches to a pressure-cycled ventilator and monitors the breathing cycle. The device, which is smaller than a deck of playing cards, includes a pressure sensor, a microcontroller, a buzzer, three buttons, and a display. It shows metrics including respiratory rate and the pressure levels in the airway during inhalation and exhalation. Clinicians use these metrics to monitor patients and adjust ventilator settings. It sounds an alarm when the pressure is too high or too low, when breathing is too fast or too slow, or too much time has passed since the last breath.
The hardware design, firmware code, and documentation for the Illinois RapidAlarm are available online with open-source licenses. The algorithm is described on the Illinois Augmented Listening Laboratory blog and the full paper can be found on arXiv.
“It was truly inspiring to have engineers from the University of Illinois’ Grainger College of Engineering, experts from Creative Thermal Solutions, and medical professionals for Carle Hospital working together quickly and efficiently to bring this device from concept to engineering prototype in such a short timeframe. The entrepreneurial spirit and engineering talent in this community clearly demonstrated the value that academic innovation ecosystems like ours provide the region, the state, and the nation,” said Prof. Singer.
Grainger Engineers are addressing the COVID-19 crisis is a variety of ways including RapidAlarm and RapidVent, personal protective equipment, COVID testing, and pandemic modeling and simulation. Singer is affiliated with both the Beckman Institute and CSL. Oelze is affiliated with both the CSL and HMNTL.
Find out more at: https://grainger.illinois.edu/news/covid-19.