Pulse Oximeter

Date of Experiment:17-2-2014

Date of submission:21-2-2014

Team 4

Chaitanyakumar D (ED11B045)

MEDICAL DISSECTION LAB REPORT

ABSTRACT

To study and understand the structure and functioning of the Pulse Oximeter. INTRODUCTION The Pulse Oximeter is a device used to measure the concentration of Oxygen in a patient’s blood. It monitors the percentage of haemoglobin that is oxygen-saturated. Oxygen saturation should always be above 95%, Pulse Oximetry is defined as the “determination of arterial saturation by analysis of bi-spectral waveforms.” Pulse Oximetry determines O2 levels of Arterial blood only and not veinous blood. This is possible due to the fact that arterial blood is pulsatile but veinous blood is not.

DISSASSEMBLY

Front UI

Mother Board

LCD Board and Battery

S.NO TASK TOOLS REQUIRED

1 Removal of back cover Screwdrivers

2 Removal of battery Hands used. No tools required

3 Removal of Circuit Board Hands used. No tools required.

DESIGN CONCEPT

Oximeters work by the principles of spectrophotometry. The relative absorption of red (absorbed by

oxygenated blood) and infrared (absorbed by deoxygenated blood) light of the systolic component

of the absorption waveform correlate to arterial blood oxygen saturations.

The light rays emitted are :-

1.RED (660 NM)

2.INFRARED (910 NM)

Oxygenated haemoglobin absorbs more infrared light and allows more red light to pass through.

Deoxygenated (or reduced) haemoglobin absorbs more red light and allows more infrared light to

pass through. This difference is utilised to determine blood saturation levels of arterial blood.

Figure 1 Absorption of Red and IR light

There are two methods for measuring O2 levels :

1. REFLECTANCE

In the reflectance method, the emitter and photodetectorare next to each other on top the

measuring site. The light bounces from the emitter to the detector across the site. 2. TRANSMISSION

In the transmission method, as shown in the figure on the previous page, the emitter and photodetector are opposite of each other with the measuring site in-between. The light can then pass through the site.

Figure 2 Transmission method

Transmission method is the most commonly used method today. Pulse Oximetry is done across reasonably translucent sites with good blood flow. In adults, the sites are finger, toe, pinna(top) or lobe of the ear. In infants, the sites are foot or palm of the hands and the big toe and thumb. At the measuring site there are constant light absorbers that are always present. They are skin, tissue, venous blood, and the arterial blood. However, with each heart beat the heart contracts and there is a surge of arterial blood, which momentarily increases arterial blood volume across the measuring site. This results in more light absorption during the surge. If light signals received at the photodetector are looked at 'as a waveform', there should be peaks with each heartbeat and troughs between heartbeats. If the light absorption at the trough (which should include all the constant absorbers) is subtracted from the light absorption at the peak then, in theory, the resultants are the absorption characteristics due to added volume of blood only; which is arterial. Since peaks occur with each heartbeat or pulse, the term "pulse oximetry" was coined.

Figure 3 Relative absorption of light

Oxygen levels are calculated using the following formula :

R = ( ac 660 / dc 660 ) / (ac 910 / dc 910 )

MODULES The various modules of the Pulse Oximeterare :-

1. User Interface/Display Buttons LCD screen Alarm

2. Power Unit Battery NI-MH Battery Pack Voltage - 6 V Capacity – 2200mAh Assembled in Korea

Charger 3. Circuit Boards

Mother Board Network resistors Diodes Inductors Electrolytic Capacitors ICs

1. 74HC245D RS232 port Power Port Peizoelectric Timer Potentiometers

LCD Board IC’s – 3 1.HT7660Made in Taiwan

4. Sensing Unit

Light Emitter Receiver Finger Clamp

HISTORY

1953 - Karl Matthes (German physician 1905–1962) developed the first 2-wavelength ear O2

saturation meter with red and green filters (later switched to red and infrared filters). His meter was

the first device to measure O2 saturation.

1940’s - The original Oximeter was made by Glenn Allan Millikan.

1964 -Shaw assembled the first absolute reading ear Oximeter by using eight wavelengths of light.

Commercialized by Hewlett-Packard, its use was limited to pulmonary functions and sleep

laboratories due to cost and size.

1972 – Pulse Oximetry was developed, by Takuo Aoyagi and MichioKishi, bioengineers, at Nihon

Kohden using the ratio of red to infrared light absorption of pulsating components at the measuring

site.

1979 - Biox was founded, and it introduced the first pulse oximeter to commercial distribution in

1981.

1995 - Masimo introduced Signal Extraction Technology (SET) that could measure accurately during

patient motion and low perfusion by separating the arterial signal from the venous and other signals.

1995 -Masimo introduced perfusion index, quantifying the amplitude of the peripheral

plethysmograph waveform. Perfusion index has been shown to help clinicians predict illness severity

and early adverse respiratory outcomes in neonates, predict low superior vena cava flow in very low

birth weight infants, provide an early indicator of sympathectomy after epidural anaesthesia,and

improve detection of critical congenital heart disease in new-borns.

2007 - Masimo introduced the first measurement of the pleth variability index (PVI), which multiple

clinical studies have shown provides a new method for automatic, non-invasive assessment of a

patient's ability to respond to fluid administration.

PRODUCT ARCHITECTURE

FUNCTIONAL DECOMPOSITION

PART SUBPART/LINKED PART FUNCTIONS

Mother Board IC’s

Network resistors

Capacitors

Peizoelectric Timer

RS232 Port

Power Port

Process and filter the noise in the values given by the light detector

Establish communication through RS232 port.

Output values to the LCD screen to be displayed out.

Pulse Oximeter

Display/User Interface

LCD Screen

Buttons

Alarm

LED Lights

Power Unit

Battery

Charger

Circuit Boards

LCD Board

MotherBoard

Network

resistors

Potentiometers

Capacitors

Power Port/

RS232 Port

Timer

Sensing/Data Input

Light

Emitter

Light Detector

Finger Clamp

Diodes

Inductor

Potentiometers

Serve as internal clock for the device.

Finger Clamp Light Emitter

Light Detector

Covering

Emit Red and IR light

Absorb light transmitted through the fingers

Prevent External light from interfering with the values

LCD Screen/ User Interface

IC’s

LCD Board

Buttons

LED lights

Alarm

Display values processed by the Mother Board

Inputs values from the user

Provides notification to the user on completion of process with alarm

Provides feedback to the user with the help of LED lights.

Connecting Cable - Transmit data and power

Outer Casing - Protects the device

GEOMETRIC LAYOUT

FUNCTION STRUCTURE

POSSIBLE IMPROVEMENTS

An improvement in mechanism allowing it give accurate values during motion and low perfusion levels

Formulate means to measure ventilation in the patient instead of solely measuring haemoglobin saturation.

Making the device more compact and easy to use. CONCLUSION The Pulse Oximeter was dissected and its components were studied. The functioning of the Pulse Oximeter was also observed. REFERENCES

1. http://www.patient.co.uk/doctor/Pulse-Oximetry.html 2. http://www.oximetry.org/pulseox/principles.htm 3. http://www.who.int/patientsafety/safesurgery/pulse_oximetry/en/ 4. http://en.wikipedia.org/wiki/Pulse_oximetry