Redesign of a Pulse Oximeter

University of PittsburghSenior Design – BioE 1161

Ted AskarSam Audia

Jeffrey JamesThomas 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.

Pulse OximeterProcessor/ Monitor

Light to Frequency Converter

CPU

Digital Display

LED Driver

VR LEDIR LED

Photodiode

1

2

3

4

Townsend et al.

1. Source sends two wavelengths of light (red, 600-700nm, and infrared 850-1000nm) through an appendage

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

98%95%93%90%88%85%81%76%70%70%

Background

Problem StatementClip Models

• Poor attachment • False alarms• Increase in caretaker workload

• SterilizationDisposable 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

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

Initial Design Considerations

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 AdhesivePolypropylene Sleeve

Reusable Sensor & Housing

Prototype 2.1 Construction

+

+

Adhesive Trimmed Adhesive

Polypropylene Sleeve

Adhesive w/ SleeveReusable Sensor

Adhesive w/ Sleeve and Sensor

Prototype Development

Prototype 1.0 Prototype 1.1 Prototype 2.0 Prototype 2.1

Disposable

PrototypeReusable

Experimental Methods

Experimental MethodsPerturbation 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

Pronated Suppinated

Wrist ExtensionWrist Flexion

Neutral

90º Pronated

Experimental Methods

Experimental MethodsCardiovascular 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

Nellcor N-200 monitor

Experimental Methods

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

ModelSupinatio

n Pronation Neutral90 º

PronationWrist 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

Hand Positions

*Ripped **Ripped and came loose

94

95

96

97

98

99

100

1

O2

Sa

tura

tio

n (

%)

Clip-on PrototypeDisposable

*

*

Cardiovascular Results

p=0.01

p=0.001

60

70

80

90

100

110

1

He

art

Ra

te (

be

ats

/min

)

Clip-on PrototypeDisposable

p=0.745

Cardiovascular Results (cont.)

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 AnalysisReusable 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 ChristophelResearcher Modeler Manufacturer Prototype TesterResearch 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 ChristophelResearcher Modeler Manufacturer Prototype TesterResearch 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