04/27/2020

Radio amateurs have succeeded in providing a complete, working ventilator system to University of Florida researchers who are in the process of applying to the Food and Drug Administration for an Emergency Use Authorization (EUA). A successful submission would blaze the way for volunteers and manufacturers around the world to create low-cost, highly functional Intensive Care Unit (ICU) or anesthesia-care ventilators that offer many of the features of modern ventilators at a fraction of the typical cost. Dr. Gordon Gibby, KX4Z, who is associated with the project, said efforts to further improve the device are ongoing.

"We made a stunning improvement in accuracy of the system and measuring volumes last night at about 1 AM," he told ARRL. "Accuracy of that particular alarm measurement went from about 300%, down to about 10%. The FDA submission is being readied, but we keep making engineering improvements."

Gibby credited some of the primary volunteers. "Bob Benedict, KD8CGH, has provided incredible volunteer testing, now exceeding 1.6 million cycles on one crucial valve and 300,000 on another. Jack Purdum, W8TEE, is the main 'code-cleaner' for one of multiple teams building software, following the initial lead of Marcelo Varanda, VA3MVV. Ashhar Farhan, VU2ESE, not only created the ventilator controller schematic but the printed circuit board layout that will be part of an expected University of Florida submission." Farhan was among the founding code writers of what we now know as Voice over Internet Protocol (VoIP).

Other hams worked on mechanical designs for flow measurements and retooled potential manufacturing capabilities otherwise used to produce transceivers. In another example of ham radio ingenuity, Marc Winzenried, WA9ZCO, modified a readily available lawn sprinkler to serve as a durable expiratory valve. This development enabled the ventilator to go more than 1 million breaths before significant valve issues developed, and the part can be replaced for less than $15.

The completed prototype in Florida was built using typical tools by a radio amateur, and assembled boards provided by LifeMech, a manufacturer working with the project. Farhan crafted an extendable menu structure for the Arduino Nano-based controller, and gas-flow measurements are made every few milliseconds by an I2C-based differential pressure transducer that can measure down to tiny PSI fractions, allowing the design to accurately track patient-induced variations in the volume of delivered gasses.

"Using Wenzenried's expiratory valve, electronic on-off control at the rate of 30 Hz allows modulation of the valve to set the continuous airway pressure used to keep the patient's lung alveoli open against virus-induced water-logging of the connective tissue," Gibby explained. An improved software design allows faster monitoring that accurately measures patient breaths despite gas flow perturbations, with the only valve component showing wear after nearly a million cycles is the nitrile diaphragm.

"Perhaps the most surprising development was the addition of the ability to sense patient effort to take a breath and immediately switch to assisting the patient with that breath, known as 'assist-control' ventilation," Gibby said. "This is expected to allow far lighter sedation of patients - potentially even no sedation - and allows patients' crucial respiratory muscles to keep up their strength." He said the current design goes far beyond the FDA's guidance document for emergency ventilator development.

Radio amateurs delivered the operational control system, basic manufacturing instructions, software, and software explanation to the University of Florida on April 24.

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