Download Design of Experiment

Volumetric Airflow Gauge
M. 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.
Introduction
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.
• 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.
Casing Design
• 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.
Objectives:
1) Interface the casing with existing BVM devices
2) Eliminate air leaks from the flow path
• 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.
3) House and protect the circuitry from damaging environments and
treatments (e.g. rain & device dropping)
4) Minimize device weight
• 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.
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
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 patient’s lungs, by
compensating for temperature expansion: V2=V1*[T2/T1]
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
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
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.