Volumetric Airflow Gauge M. Chakan, J. Kiswardy, M. Nilo - PowerPoint PPT Presentation

Title: Volumetric Airflow Gauge M. Chakan, J. Kiswardy, M. Nilo


1
Volumetric Airflow GaugeM. Chakan, J. Kiswardy,
M. Nilo
Abstract Individuals suffering from
cardiopulmonary failure and other types of
respiratory distress are commonly treated with a
manual resuscitation device in order to initiate
breathing. In many instances, excessive or
insufficient air volume delivery occurs as a
result of the user incorrectly estimating the
amount of air administered to the patient. As a
result, side-effects including lung tissue
damage, gastric distension, and regurgitation
have been observed. A volumetric airflow gauge
was developed that provides the user with an
accurate display of the volume introduced to the
patients airway with each inflation/deflation
cycle of the resuscitator device. The gauge is
comprised of an electric circuit board that
directly measures the airflow volume powered
through the use of two external 9V batteries. A
non-reactive plastic was used to construct the
housing for the electrical components, permitting
the device to be incorporated with relative ease
into most standard manual resuscitators. The
device will provide a cost-effective method for
the user to accurately determine and control the
amount of air he/she is administering to the
traumatized patient.
Figure 1. Volumetric Airflow Gauge circuit
schematic.
Following completion of circuit assembly (Figure
2), a battery-life test was performed to
determine the functional device time before
battery warnings were indicated. A test was
performed that powered the entire circuit from
one battery, while another test was performed
that used two batteries one powering the airflow
sensor and one powering the remaining components.
Additionally, accuracy tests are planned to
compare the volume measured by our device with
the volume measured by a human simulator. The
difference in volume will undergo statistical
testing (i.e. a t-test) to determine the device
error. Casing Design Objectives 1) Interface the
casing with existing BVM devices 2) Eliminate
air leaks from the flow path 3) House and
protect the circuitry from damaging environments
and treatments (e.g. rain device dropping) 4)
Minimize device weight Solutions 1)
Input/output ports were designed to fit existing
BVM hardware 2) The mass-flow sensor
input/output ports were snugly fit into the
input/output ports of the casing, and reinforced
with rubber gaskets 3) A robust casing was
designed to snugly fit the circuitry, while
rubber gaskets were added between joints to
repel water 4) The prototype was first developed
in SolidWorks, where the casing mass was
determined and altered through continual redesign
Introduction The United States 911 emergency
call center receives an average of 500,000 calls
daily of these approximately 35 involve
individuals with some type of cardiopulmonary
failure. Most common method of initiating
breathing in an individual suffering from cardiac
arrest or pulmonary failure, aside from CPR, is
through the use of a manual resuscitator or
bag-valve-mask (BVM) system. Efficacy of
resuscitation using a manual BVM is highly
dependant on the training and skill level of the
user and, as a result, many potential
complications exist, the most significant
involving over/under inflation of the patients
airway. Well documented side-effects include
Lung tissue damage
Decreased lung compliance
Gastric distension
Regurgitation These side-effects frequently
lead to co-morbidities involving increased
hospital stay and cost incurred by the patient.
A solution needs to be presented that would allow
the user to better estimate and thereby control
the amount of air that is introduced to the
patients airway while using a manual BVM system.
Project objective was to design a gauge that
could be easily incorporated into a manual
resuscitation device, providing the user with a
constant volumetric display of air introduced to
the patient. The device will potentially
minimize the undesired side-effects associated
with under/over inflation mentioned previously.
Results A prototype of the Volumetric Airflow
Gauge has been developed and constructed (Figure
2 for circuit Figure 3 for casing). Initial
battery-life tests indicated that the use of one
9V battery permitted a circuit life of 10
minutes, while the use of two 9V batteries
increased the circuit life to 120 minutes.
Materials and Methods The overall design involved
two separate components electrical circuitry
(Figure 1), which measures and displays the
inspiratory air volume of the BVM to the user,
and a casing that houses the circuitry and
provides a streamlined product that easily
incorporates into existing manual resuscitators.
Circuit Design Objectives 1) Measure an
airflow between 0 and 1.6 L/s 2) Sample,
calculate, and display the air volume in near
real-time 3) Display the volume with a precision
of 10 mL 4) Calculate the effective volume of
air that entered into the patients lungs, by
compensating for temperature expansion
V2V1T2/T1 5) Warn the user when to replace
the batteries 6) Provide a rescue breathing rate
metronome to aid proper ventilation
technique Solutions 1) Use a mass-flow sensor
(AWM720P1, Honeywell) which measures an airflow
between 0 and 3.3 L/s 2) Use a microcontroller
(PIC18F2321, Microchip Technology) with 512 bytes
RAM, 8 kbytes ROM, and a 40 MHz oscillator 3)
Use a 3-digit LED display (LDT-C514RI, Lumex) to
display volumetric readings 4) Incorporate a
thermistor (MCP9700A, Microchip Technology) to
measure ambient air temperature 5)
Independently sample the battery voltages and
display low battery voltages with LEDs 6)
Include an independent timing program to control
an LED
Figure 2. Completed circuitry of the Volumetric
Airflow Gauge. Front Numerical volumetric
display and LED indicators Back Mass airflow
sensor Top left Thermistor
Figure 3. SolidWorks model of the Volumetric
Airflow Gauge casing Left Battery compartment
and door Center Void for the completed circuit
Right Cap to enclose circuit and direct flow
through airflow sensor
Discussion A prototype of the Volumetric Airflow
Gauge has been successfully developed and
constructed. Upon successful completion of the
accuracy verification tests, the volumetric
airflow gauge will be a proven, practical device
that will provide the user with an accurate
display of the volume of air introduced to the
patient during resuscitation. An accuracy of /-
50 mL will help minimize the potential for
over/under inflation of patients airways during
manual resuscitation with a BVM. In addition, the
simple design of the device allows rapid user
comprehension and ease of use. Further
validation of the device will be performed by
specialists in the Emergency Medicine field.
These voluntary specialists will have an
opportunity to test the device and provide
feedback based on their observations, thus
providing additional confirmation of the benefits
of the device.
Acknowledgments The authors thank Dr. Hal
Wrigley, Dr. Linda Baker, the BioEngineering
Department, Guy Guimond, and Eric Reiss for their
generosity and support.