The Institute - September 2020 - TI8

tech takes on COVID-19

Why DIY Ventilators
Are Still a
Vital Stopgap

OVID-19 patients can find
it difficult to breathe as the
virus infects their respiratory
tract. Severe cases result in edema-a
buildup of fluid-and failure in the alveoli, the small pockets in the lungs that
exchange oxygen and carbon-dioxide
molecules with the bloodstream.
Respiration being an absolute requirement for life, it is not surprising that
the mechanical ventilators found in
intensive-care units have been in great
demand during the COVID-19 crisis. The
ventilators use a mobile compressor to
assist with the patient's breathing by
pushing air through a tube placed in
the trachea to expand the lungs.
At times, the need for mechanical
ventilators has far outpaced the number available. There have been many
efforts to address the supply shortage.
For example, some car companies have
adapted existing designs of ventilation equipment and are manufacturing
them at their facilities. Established ventilator manufacturers have increased
production while also making some of
their designs freely available.
While those endeavors aim to produce ventilators that are close to the
current standard medical equipment
used in ICUs, we are also seeing a wave
of interim DIY devices being developed to increase the supply [page
TI- 6]. These rapidly scalable, low-cost

TI-8

SEP 2020

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emergency ventilators (EVs) are mainly
the automated version of manual bagbased resuscitator devices, commonly
known as Ambu bags or bag valve
masks (BVMs).
The small, compact, balloonlike
bags have a soft air reservoir that can
be squeezed by medical professionals to inflate a patient's lungs. Oxygen is administered via tubing to the
bag. Exhalation occurs due to elastic
recoil of the patient's chest, and the
bag resumes its original shape.
BVMs can theoretically support a
patient indefinitely, but in reality, it
is a temporary measure, as manual
compression is tedious and lacks good
control.
The DIY emergency ventilators
address that issue by automating
the squeezing of the bag. They are
open-source and typically built using
off-the-shelf parts, widely available
materials, and simple fabrication and
assembly techniques. A few examples
are those from MIT (E-Vent), Oxford
University and King's College London (OxVent) and the University of
Glasgow (GlasVent).
Almost all use a motor or air compressor to squeeze the BVM. The
motor's speed or the air compressor speed controls the breathing rate,
and the plunger controls the level of
BVM compression. The amount of

compression determines the tidal
volume-the volume of air entering
and exiting the lungs with each breath.
The attributes of those initiatives
are their fast deployment, scalability,
simple assembly, compact size, and
low cost. The devices are meant to be
used only for short periods of time-up
to a few hours. The GlasVent offers an
additional feature: It can be operated
manually by someone with little or no
medical experience.
EVs offer some of the same features as mechanical ventilators and
could be useful in emergency situations where the availability and cost
of standard ones is limiting. The cost
per mechanical ventilator ranges from
US $20,000 to $100,000, which by no
means makes it a cheap intervention.
On other hand, the cost of an EV could
be as low as $100.
In addition, because EVs can be powered through the main supply, batteries, or manually in the case of GlasVent,
they can be used during power outages. Also, their compact size allows
them to be deployed in ambulances
and even cars.
VENTILATION BASICS

Even though EVs might seem relatively
simple from an engineering perspective, designing a ventilator that can
be used safely and reliably to help a
person breathe is a significant challenge. Those who intend to develop
DIY EVs need to understand some
fundamentals.
There are many ways to supply ventilation to a patient. Depending on the
patient's breathing efforts and sedation
and the pressure or volume control,
the ventilation can control the breathing entirely or just provide assistance.
Optimal ventilator parameters vary
between patients and can change

https://spectrum.ieee.org/cars-that-think/biomedical/devices/coronavirus-news-automakers-ford-gm-pivot-produce-ventilators-respirators-face-masks https://www.scitechdaily.com/mit-team-races-to-fill-covid-19-ventilator-shortage-with-low-cost-open-source-alternative/ http://www.ox.ac.uk/news/2020-03-31-ventilator-project-oxvent-gets-green-light-uk-government-proceed-next-stage-testing http://www.ox.ac.uk/news/2020-03-31-ventilator-project-oxvent-gets-green-light-uk-government-proceed-next-stage-testing http://www.ox.ac.uk/news/2020-03-31-ventilator-project-oxvent-gets-green-light-uk-government-proceed-next-stage-testing https://www.gla.ac.uk/research/az/best/diyventilator/ https://www.gla.ac.uk/research/az/best/diyventilator/

The Institute - September 2020

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