IEEE Robotics & Automation Magazine - March 2021 - 106

Inspiratory Pressure

40

PPIP

35

Volume (mL)

Pressure (hPa)

25
20
PPEEP

15

TV

500

Pplat

30

TV

600

400
300
200

10
100

5
0

0
0

0.5

1

1.5

2

2.5

0

0.5

1

1.5

Time (s)

Time (s)

(a)

(b)
σ for n = 30

2

2.5

Mean

Figure 3. The typical VCV waveforms generated by the VOV, averaged over 30 respiratory cycles: (a) the characteristic airway pressure
profile with callouts to clinically relevant pressure landmarks and (b) the characteristic TV.

Vanderbilt University Medical Center, we defined the functional
requirements to guide our electromechanical design decisions
(summarized in Table 1). We did so with the general goal of
generating a design that is low cost, largely insensitive to supply
chain disruptions and material accessibility limitations, and easy
to manufacture. The range of adjustable TV, BPM, and I/E
(reported in Table 1) ensures that our design will be able to
accommodate a wide range of patients suffering from compromised respiratory function. COVID-19 patients are typically
ventilated at a rate of 20-35 BPM and an I/E ratio from 1:1 to 1:2
[23], while some outlying pathologies may require rates as high
as 50 BPM and I/E ratios as low as 1:4 [24]. Clinical wisdom dictates that TV should be initially selected based on patient weight
(6 mL/kg) and finely tuned ad hoc according to Pplat, PPEEP, and

Table 1. The list of VOV functional requirements.

106

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Parameter

Value

TV

0-800 [mL] (adjustable)

Maximum TV deviation (long term)

35%

Respiratory rate

5-55 [BPM] (adjustable)

BPM repeatability (over 1 min)

±1 [BPM]

I:E ratio

1:1-1:4 (adjustable)

Continuous operation

>14 [days]

Maximum deliverable PPIP

>40 [hPa]

PPEEP

0-25 [hPa] (adjustable)

Barotrauma pressure limiting?

Yes

Over-/under-pressure reporting?

Yes (adjustable)

IEEE ROBOTICS & AUTOMATION MAGAZINE

*

MARCH 2021

lung compliance [23]. A TV range of 0-800 mL ensures that we
can accommodate the 95th percentile American male and 99th
percentile American female. Active pressure detection and TV
compensation will ensure that patients being ventilated are protected from anomalous and potentially traumatic pressure
events and that the physician is subsequently alerted to such
events to modify the clinical parameters or convert to manual
ventilation if necessary.
Mechanical Design
We approached the VOV design challenge by first identifying
the actuator and structural materials, given the general constraints of availability, cost, and manufacturability. We selected the windshield wiper motor for its low cost, global
availability, and ease of sourcing (from auto manufacturers to
junk yards). Furthermore, the worm gear mechanism inside
the motor is designed to generate large forces at a range of
speeds under extreme conditions, from subfreezing to
extremely hot (>37 C°) environments. These features make
windshield wiper motors excellent candidates for applications
that require reciprocating, low-to-medium speed actuation
for millions of cycles.
For the structural material, plywood was selected, also for
its availability and the relatively simple and inexpensive tools
required to cut it into useable parts. Cabinet makers, wood
workers, and many hobbyists have the tools and know-how to
make all of the mechanical parts.
SYM
Given these materials and constraints, the SYM offers a simple,
relatively low component count and low fabrication-precision
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