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C8A3 Prototype Build Review

Concept C8A3 - Prototype Build Review

@jd18 05 APR 2020

Positive Comments

  1. Many Design Criteria Met

    • Must squeeze bag with sufficient volume displacement
    • Must avoid friction between mechanism and bag to lowest degree
    • Must accept placing the bag (Transition from pumping to loading) or a port for manual bag transitions.
    • Must be able to be sterilized and/or used in a sterile environment
    • Must be able to be on it’s own cart or hang from IV Stand - solve limited table space.
    • Must be able to replace BVM or similar core pump with ease.
    • Must protect the bag from accidental contact from bumps, drops, other equipment
    • Must have the ability to disassemble easily for repair/cleaning
      • How do you clean the sides of the flapper? Need a "clean" button that would push it all the way up?
    • Must be able to reach volumes of 1000 per day in industrial facilities
    • Must use as few parts as possible
    • Must Be physically robust enough for rough handling
    • Must have low friction bearings on any high frequency rotating components

  2. Overall Look/Feel is very positively received, quite professional, likely to be acceptable to reviewers because of its "medical device vernacular"

  3. Safety and Cleanability strong positives.

  4. Basically everything on the outside looks great, and the mechanism seems simple, but control will be complex....

Neutral Comments

  1. Design Criteria in Question
    • Must have and easy and apparent control interface
      • n/a Where would you propose the control hardware and UI live?
    • Must have simple adjustment for on the fly volume/displacement changes on the device
      • n/a today, but presumably via UI later.
    • Must have simple adjustment for on the fly pressure changes on the device
      • n/a today, but presumably via UI later. Challenge in this design without in-patient-line pressure/flow readings.
      • Feeding back force on the flapper may not be direct enough, also a challenge to be highly accurate
    • Must have a small pole (Beacon) indicating alarms and continuous function
      • n/a today. where would we put this?
    • Must allow sensing and control for key MVP and Testing Specs
      • Control and sensing may be challenging, or expensive, or likely both.
    • Must allow for sensing of current actuator location / bag displacement
      • n/a today

Next Iteration Challenges

  1. Mechanical core is an unknown quantity.

    • Can a bushing/coupling/follower combo be designed for HIGH reliability and consistent force delivery to the flapper over its lifetime?
    • Where should the motor be mounted?
      • Do we have enough authority over pressure and volume at that location?
      • Precision?
      • How non-linear is it? At what points in the cycle?
    • How does it deal with extreme back-pressure transients (patient cough, tube kinked, e.g.)
    • How does it deal with extreme force feedback (mechanism binds, user leans on it e.g.)
      • presumably the stepper will just skip steps but follower could strip, etc - How does it reset or react under these circumstances?

  2. Cost / Complexity

    • Current design approach requires pressure and flow sensing in the patient breathing line.
      • Medical-grade Flow sensors may be expensive (XXX euros/dollars?) and may be in difficult supply chains (global push to build vents)
      • Custom Flow sensors would need significant testing and sterilization protocols for approval, and likely require multiple pressure sensors.
    • Real-time sensor feedback to squeezer position/force/speed may be non-linear and therefore per-breath control may be all that's safe e.g. feedback changes settings for the next breath cycle, more of a calibrated look-up table for settings than a real control loop.

Team Lead(s):

Team Gitlab Slack
Acme @jd18 @ Jonathan Kemp
Edited by Jonathan Kemp