University of Pittsburgh
Senior Design – BioE 1161
Redesign of a Pulse Oximeter
Ted Askar
Sam Audia
Jeffrey James
Thomas Christophel
April 13, 2004
Mentor: Sandra Gartner, RN
Background
What is a pulse oximeter?
• Non-invasive tool for monitoring the percent
concentration of hemoglobin (Hb) saturated with oxygen.
Processor/ Monitor
Pulse Oximeter
Background
1. Source sends two wavelengths of
light (red, 600-700nm, and infrared
850-1000nm) through an appendage
3
Light to
Frequency
Converter
Photodiode
2. Blood Hb absorbs red light while
O2Hb absorbs infrared light
3. Photodiode measures LED intensities
4. A processor calculates the
absorbance ratio which is then used
to determine oxygen saturation
2
IR LED
VR LED
1
LED Driver
76%
81%
85%
88%
90%
93%
95%
98%
70%
CPU
4
Digital Display
Townsend et al.
Problem Statement
Clip Models
• Poor attachment
• False alarms
• Increase in caretaker workload
• Sterilization
Disposable Models
• Single use
• Non-reusable sensor
• Costly ~$16+ per unit
• Off-label use
Semi-disposable models
• Complicated design
• High cost disposable wraps
• High cost reusable sensors
• Sterilization (sensor contacts skin)
Project Requirements
Maintain attachment
Minimize cost
• Reduce caretaker workload
• Reduce cost per unit
Sterilization considerations
Easy to use
Audience
• Can be used in any traditional pulse oximeter
application
• Any patient requiring monitoring of heart rate or O2
saturation
Initial Design Considerations
Reusable model improvements
• VelcroTM
• Stronger clip
Disposable model improvements
• Cheaper materials
Semi-disposable model improvements
• Simpler adhesive/wrap design
• Eliminate contact between sensor and skin
Proposed Solution
Disposable adhesive
• Maintains proper positioning
• Cost effective alternative to other disposable models
Polypropylene Sleeve
• Eliminate need for sterilization (no sensor contact)
• Ease of use
Reusable sensor
• Low cost sensor
• Durable housing
Prototype 1.1
Disposable Adhesive
Polypropylene Sleeve
Reusable Sensor & Housing
Prototype 2.1 Construction
+
Trimmed
Adhesive
Adhesive
Polypropylene
Sleeve
+
Reusable
Sensor
Adhesive w/ Sleeve
Adhesive w/ Sleeve
and Sensor
Prototype Development
Prototype 1.0
Prototype 1.1
Prototype 2.0 Prototype 2.1
Experimental Methods
Disposable
Prototype
Reusable
Experimental Methods
Perturbation testing
• N=1 subjects
• 3 pulse oximeter models tested
• Disposable, Reusable, and Prototype
• Subject positioning
•
•
•
•
•
Sat adjacent to testing table
Shoulder approx. in 60° of abduction in the coronal plane
Elbow approx. 0 degrees in the sagittal plane
Elbow approx. at 90° of flexion
6 different hand positions
• Task
• Dropped 200gm weight to simulate a “yank” or pull on pulse
oximeter cord
• Repeated 5 times for each hand position
• Data acquisition
• 1 if adhesive came off
• 0 if adhesive stayed on
• * if adhesive ripped or came loose
Experimental Methods
Pronated
Suppinated
Wrist Flexion
Wrist Extension
Neutral
90º Pronated
Experimental Methods
Cardiovascular monitoring testing
• N=4 subjects
• 3 pulse oximeter models tested
• Disposable, Reusable, and Prototype
• Subject positioning
•
•
•
•
•
Sat adjacent to testing table
Shoulder approx. in 60° of abduction in the coronal plane
Elbow approx. 0 degrees in the sagittal plane
Elbow approx. at 90° of flexion
Palm rested on table
• Task
• Assess subject O2 saturation and heart rate
• Repeated 5 times for each model
• Data acquisition
• Nellcor N-200 monitor
Experimental Methods
Nellcor N-200
monitor
Data Analysis
MS Excel ™
• Data collection
• Data analysis
• Averages
• Standard deviations
• Figure/Table creation
SPSS™
• Data analysis
• Repeated measures ANOVA
• alpha value = 0.05
• Post Hoc
• Paired T-Test
Perturbation Results
Hand Positions
Model
Supination
Pronation
Neutral
90 º Pronation
Wrist Flexion
Wrist Extension
Clip on
0
5
5
5
5
0
Prototype
0
0
0
0
0*
0
Disposable
0
0
0
0
0**
0
*Ripped
**Ripped and came loose
Cardiovascular Results
*
*
100
p=0.001
p=0.01
O2 Saturation (%)
99
98
97
96
95
Clip-on
Disposable Prototype
94
1
Cardiovascular Results (cont.)
110
Heart Rate (beats/min)
p=0.745
100
90
80
70
Clip-on
Disposable Prototype
60
1
Discussion
Our testing showed:
• Equivalence to predicate device
(Nellcor D-25 Oxisensor ® II)
• Maintenance of attachment to digit
Economic Benefits
Significantly lower price
• Low cost reusable sensor
• Low cost disposable adhesive sleeve
Market size
• 33.6M per year (US hospital patients)
New York Times (www.chetday.com/medmistakes.html)
Distribution
• Medical supply companies
Competitive Analysis
Reusable pulse oximeters (clip)
• Nellcor Durasensor ®
• $250
• Nonin Onyx ®
• $395
Disposable pulse oximeters
• Nellcor Oxisensor ® II
• ~ $16 per single use unit
Semi-reusable pulse oximeters
• Nonin Flex Sensor System
• $107 reusable sensor
• $0.85 replaceable wrap
• Nellcor Dura-Y®
• $371 reusable sensor
Competitive Analysis
Strengths
• Price
• Sensor equivalent to disposable models (~$16)
• Disposable adhesive sleeve equivalent to wraps (< $1)
• Secure attachment
• No contact between sensor and skin
Weaknesses
• No competitive sensor design
• No competitive processor/monitor design
Constraints
Economic
• Origin of medical grade materials
• Origin of electrical components
• Outside distributor costs
Regulatory
• Limited exposure biocompatibility testing
• Cytotoxicity
• Sanitization
• Irritation or intracutaneous reactivity
Quality System Considerations
Manufacturability
• Simple Design
• 3M Transpore ® adhesive
• Polypropylene sleeve
• Encase sensor/emitter in pliable rubber
Human factors
• Ensure biocompatibility of disposable
adhesive sleeve
• Insulate electrical components
• Ease of use
FDA Regulation
TITLE 21--FOOD AND DRUGS
•
•
•
•
CHAPTER I—FOOD AND DRUG ADMINISTRATION
DEPARTMENT OF HEALTH AND HUMAN SERVICES
PART 870--CARDIOVASCULAR DEVICES
Subpart C--Cardiovascular Monitoring Devices
Sec. 870.2700 Oximeter.
(a) Identification. An oximeter is a device used to transmit radiation
at a known wavelength(s) through blood and to measure the blood
oxygen saturation based on the amount of reflected or scattered
radiation. It may be used alone or in conjunction with a fiberoptic
oximeter catheter.
(b) Classification. Class II (performance standards).
US Food and Drug Administration: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=870.2700
Project Goals
Research
• Potential hazards
• Sensor designs
• Types of adhesives
Design
• Low cost reusable sensor that maintains accuracy of
current competitors
• A disposable adhesive that maintains attachment
Prototyping
• Acquire materials
• Construct a prototype
Testing
• Prototype vs. disposable and reusable models
Task List – BioE 1160
Audia
James
Askar
Christophel
Researcher
Modeler
Manufacturer
Prototype Tester
Research the
potential hazards.
Conceptual design
Circuit design of
pulse oximeter
Pilot test the new adhesive
with pulse oximeter
Research current
pulse oximeters
(competitors)
Model the adhesive
Purchase
adhesives and
pulse oximeters
Test new adhesive design
verses current models.
Research possible
size, type, and
shape of adhesives.
Model the pulse
oximeter
Assemble prototype
device
Perform data analyses of the
results
Specific aims
(SBIR)
Relevant
Experience (SBIR)
Significance (SBIR)
Experimental Design and
Methods (SBIR)
Updated Task List – BioE 1161
Askar
James
Audia
Christophel
Researcher
Modeler
Manufacturer
Prototype Tester
Research the
potential hazards.
Conceptual design
Circuit design of
pulse oximeter
Pilot test the new adhesive
with pulse oximeter
Research current
pulse oximeters
(competitors)
Model the adhesive
Purchase
adhesives and
pulse oximeters
Test new adhesive design
verses current models.
Research possible
size, type, and
shape of adhesives.
Model the pulse
oximeter
Assemble prototype
devices
Perform data analyses of the
results
Specific aims
(SBIR)
Relevant
Experience (SBIR)
Significance (SBIR)
Experimental Design and
Methods (SBIR)
Project Results
Research
Design
• Conceptual design
• Disposable adhesive sleeve
• Reusable sensor
Prototyping
• Four prototypes developed
Testing
• Perturbation tests
• Cardiovascular monitoring tests
Future
• Recycling program for disposable pulse oximeters
• Means of acquiring low cost components
• Easily made compatible with disposable adhesive sleeve
• Design emitter/sensor for use with our adhesive
• Develop a durable sensor housing
• Design a monitor for our system
Acknowledgements
Sandra Gartner, RN
Mark Gartner, M.S.
Shouchen Dun, M.S.
Jesse Fisk, M.S.
Funding: Department of Bioengineering