Hacking an Automatic Blood Pressure Cuff: DIY Ventilator

Utilizing existing medical equipment and hobby electronics to meet the emergency ventilator shortage

Emergency ventilator CAD model, using an automatic blood pressure monitor/cuff to squeeze an Ambu-bag.

Update Log

This project is actively in development, and this post will be updated regularly.

Initial Posting: 4/13/20

Won Columbia Design Challenge Grant: 4/27/20

The Team & Challenge

From left to right: Millen Anand (ma3617@columbia.edu), Ginny Jeong (hj2502@columbia.edu), Nathalie Limandibratha (nbl2116@columbia.edu), Connor Evans (cde2119@columbia.edu).

All team members are undergraduate senior mechanical engineers from Columbia University. The team is participating in the Columbia DIY Ventilator Challenge, with the goal of designing a makeshift emergency ventilator based on an Ambu-bag that can be used both for invasive ventilation (in hospital settings) and potentially for non-invasive ventilation using a mask. The device will squeeze this bag automatically at a specified amplitude and rate, and will be used to keep patients alive while they wait for a proper ventilator.

We are actively seeking additional funding to prototype this design and feedback from HCPs and engineers. We posted our design publicly in hopes that other innovators will iterate on our design (contact us via email for CAD files).

Design Objectives

1. Zero Manufacturing: Simpler; increases modularity; cheapest and fastest; no need for technician or engineer; globally adaptable
2. Utilize Existing Hospital Equipment: Medical-grade, reliable; Hospitals have many automatic Blood Pressure (BP) monitors (source: Johns Hopkins, Mount Sinai)
3. Meet Need for Large Quantity: Ventilator need increasing exponentially in the US, Commercial ventilator production too slow

Building Off a Proved Design

Manual Blood Pressure Cuff Ventilator (Dan Bruder)

Dan Bruder (PhD student, University of Michigan) posted a guide to creating a DIY Ventilator using a manual blood pressure cuff (video). His design proved feasibility of this technology, made use of ubiquitous medical blood pressure cuffs, and featured an adjustable breathing rate.

This design is reliant on health care professionals (HCP) having compressed air and vacuum outlets, and had no digital pressure sensor or screen for the HCP to interact with. Our team set out to improve these aspects of the design, as well as take advantage of the fact that most hospitals in the US utilize automatic blood pressure monitors with built-in pumps and valves.

Our Design: Automatic Blood Pressure Monitor Ventilator

Automatic Blood Pressure Cuff Ventilator, shown without wiring and electronic components.

Advantages of Automatic BP Monitor

1. Prevalent in hospitals: utilizing medical-grade equipment; Hospitals have many automatic BP cuffs (Johns Hopkins, Mount Sinai)
2. Repurposable: Cheaper/easier than fabricating actuation mechanism; Perfect compressive function; monitors already have pump, solenoid valve, tubing
3. Adjustable / Flexible: Any automatic BP device brand or model works; Easily accommodate different BVM sizes; Easy override if automatic ventilation fails — unstrap for manual ventilations
4. In-line pressure measurement: Enables accurate pressure measurement by use of cuff pressure; Sanitary as air volume of BVM and BP cuff don’t interact

Device Functionality & Airflow

Components native to most blood pressure monitors include pumps, solenoid valves, and tubing.

For compression, the solenoid valve is closed to the atmosphere and compressed air from the pump flows through the outlet to the cuff. Ambu-bag is squeezed and air is delivered to the patient.

For decompression, the solenoid valve is opened to the atmosphere, allowing the cuff to decompress and the Ambu-bag to release.

Electronics Subassembly

Simple hobby electronics enable powerful control and adjustment capabilities for HCPs.

Basic Specifications

1. Min/Max Pump Rate: 0–34 pumps/min, adjustable with potentiometer
2. Amplitude Range: 0–6 in (verify with testing), adjustable with potentiometer
3. Sensed Conditions: Ambu-bag pressure, cuff pressure
4. Safety Measures: Ambu-bag pressure drop alarm, cuff disconnect alarm

Full Parts List & Construction Info

At only $118.44 additional cost per ventilator to hospitals, the design enables large-scale ventilator production.

The only tools needed for construction are a screwdriver (for blood pressure monitor disassembly) and a wire cutter (for circuitry). No manufacturing necessary, meaning anyone can assemble.

The estimated construction time is 30 minutes: 5 min disassembly, 15 min wiring, 10 min code setup.

Caveats & Disclaimers

There are several issues yet to be tested and ironed out. These will be updated as assumptions are tested.

1. Pump inflation effectiveness: Achievable breath rate with built-in pump will need to be verified to ensure full breath rate range is possible.
2. Adjusting for different BP monitors: Current design is based on Omron BP monitor. Different monitors have varying air pump components, which may affect voltage settings. Most automatic BP monitors operate very similarly, but will require testing and calibration of different monitors to verify.
3. Determining voltage settings: Voltage is critical to determine compression rates and amplitude. Will be determined through experimentation.
4. Drop in pressure in Ambu bag: Most accurate pressure sensor is in the BP monitor and not in the Ambu bag. A pressure sensor (force sensitive resistor) between the Ambu bag and plywood base will be tested to determine effectiveness.

References & Acknowledgements

Design Proof of Concept: Dan Bruder

DIY Ventilator Using Common Medical Supplies

Electronics

Arduino - DC Motor

Controlling a Solenoid with an Arduino - Tutorial

Medical Personnel

Lynn Leville — Nurse at Mount Sinai Hospital

Ricky Winardi — General Practitioner at Kaiser Permanente (Sacramento)

Sarah Teitell — Pediatric Resident at Kaiser Permanente (Oakland)

Elise Thompson — EMT at Metro West Ambulance (Oregon)

Michelle Bosché — EMT at Columbia University Emergency Medical Service

Shannon Bosché — Masters of Nursing at Johns Hopkins PICU

© 2020 Millen Anand, Ginny Jeong, Nathalie Limandibratha, Connor Evans. All Rights Reserved. Patent Pending.