Someone is getting an education. In the last week a lot of progress has been made. InqVent has been added to Dr. Robert Read’s COVID-19 Vent List and I’ve joined Helpful Engineering. Think of them as clearing houses of doctors and engineers collaborating to create COVID-19 emergency ventilators. The former is razor focused on ventilators alone, while the latter is tackling the COVID pandemic from all angles. There are individuals, small groups, universities, small companies and large corporations collaborating (or at least sharing their knowledge) to give the world a fighting chance. Please check out these sites and consider contributing your time, skills or even financially to a promising project.
InqVent, version 10 met all the requirements asked of it. Unfortunately, not enough was asked. Some of my early research and feedback from the medical industry must have been based on pre-COVID-19 usage patterns. The two sites above have proven to be invaluable. The greatest leaps in my education of the medical requirements came through a four volume set of requirements from Dr. Erich Schulz. Dr. Schulz and Dr. Read’s contributions have provided a great service to the world. Before their work, my design criteria for InqVent was spotty at best. From an engineer or software developers standpoint GIGO (garbage in – garbage out). In his four volume set, he not only describes what is necessary, he explains it in layman (non-medical) terms even us engineers can understand. We just have to take heed. This helps the Inquisitive among us to understand why a requirement is necessary.
InqVent, version 11 was started pre-revelation. It was simply meant to tackle using PLA plastic instead of ABS to permit a larger spectrum of Makers access to helping build InqVent. ABS tends to be a PITA and some people cannot tolerate the fumes. ABS requires higher temperatures that some printers can’t handle. It also is far more susceptible to air drafts during the print and higher dimensional changes due to CTE and the higher temperature. You pretty much need to have your printer in an enclosed chamber. The PLA plastic results look very good and will be incorporated moving forward. But now, I’m on to version 12.
InqVent, version 12 is being designed
Version 10 already uses smart processing to follow medical industry designated pressure versus time curves. Deviation from the curve is less than 4%. The total area under the curve (what the patient actually experiences) is accurate within 0.1%! It can sustain breaths cycling to within millisecond accuracy. Because it does not use an Ambu Bag design, it has near instance response. Square-wave pressure-time curves are easily tracked with its huge volume rate reserves of over 600 liters/minute.
Its limitation unfortunately… It was primarily designed to handle a baseline peak pressure of 10 cm-H2O. Even though it was capable of over 30 cm-H20, longevity was being counted on by its low %10 duty cycle at 10 cm-H2O. This was what initial research indicated was the most common and would be quite useful. Apparently, that research data point was in error… at least for COVID-19 patients. 40 cm-H2O is the criteria by which a COVID-19 emergency ventilator will be judged. A new, more powerful air-drive system will be employed. The air-drive system will not be integrated within InqVent allowing viable, regional substitutes to quickly be utilized. Using regulated hospital medical air will also be an option.
Another goal for Version 12 is patient triggered control. Early research indicated this was a, “nice to have” feature. Although, I tested Version 10 for its ability to utilize this and found it could detect inhalation, it was never a priority. After study of Dr. Schulz’s papers, I now understand how it is not only nice to have, but vital. Any system without it, is not really usable for COVID-19. In a nut-shell, that even this engineer easily understands… If the patient is not triggering the breath, they must be sedated so their system accepts the machines control. This take more medical oversight and makes it harder and takes longer to wean the patient back controlling their own breaths. Additional sensors will be added to measure air flow rates and more AI intelligence will be added to seamlessly transition to and from full control to patient triggered control in Version 12. InqVent is getting an education too.
Cost
The major cost will be time. This is likely to take several weeks. Just getting and making new equipment for flow testing and validation will take time. Stay tuned! I’ll keep the posts coming on the status. Monetary cost is trivial. My current expectation is that a full functional InqVent will still be less than $100 US. Consider that most of the non-intelligently controlled Ambu Bag designs cost well north of $100.