This document discusses pulse oximetry and pulse oximeter design. It explains the working principles of transmittance and reflectance pulse oximeters, how they calculate oxygen saturation levels, and potential sources of error. Key points covered include the use of red and infrared light to measure oxygenated and deoxygenated hemoglobin, Beer's and Lambert's laws regarding light absorption, and the signal processing and calibration methods used to determine oxygen saturation values. Design considerations for pulse oximeter sensors, testing parameters, and general software models are also summarized.

1. PRADEEP KUMAR YADAV
M.Tech IIT hyderabad
biomedical engineer - QA
PaO2 < 80mmHg – hypoxemia
1.Hypoxic hypoxemia
¯ PaO2 ¯ SaO2 – Normal Hb
2.Anaemic hypoxemia
¯Hb , Normal PaO2 & SaO2
3.Toxic hypoxemia
¯SaO2,Normal PaO2

2. Transmittance based Pulse oximeter
Pulse Oximeter used to measure oxygen saturation in the body i.e
how much of the hemoglobin in the blood is carrying the oxygen.
http://embedded-lab.com/blog/introducing-easy-pulse-a-diy-
photoplethysmographic-sensor-for-measuring-heart-rate/

3. Oxygen saturation
 Oxygen enters the lungs and then is passed on into blood. The
blood carries the oxygen to the various organs in our body. The
main way oxygen is carried in our blood is by means of
hemoglobin.
 Normal oxygen saturation values are 97% to 99% in a healthy
individual on room air.

4. Hb and oxygen

5. Working principle
 Pulse Oximetry consists of Red(R) and Infrared(IR) light
emitting LEDs and a photo detector.
 Oxygenated and deoxygenated hemoglobin have different
light absorption rate.
 Oxygenated hemoglobin absorbs more infrared light
 Deoxygenated hemoglobin absorbs more red light
https://drive.google.com/drive/u/1/folders/12MOdf83nIdT3UP154mMbBPF3fT
OW2m3j

6. Calculations
This ratio corresponds to Sp02
0.5 is approx 100%
1 is approx 85%
2 is approx 0%
https//www.nxp.comdocsenapplication-noteAN4327.pdf
https://www.sciencedirect.com/science/article/pii/S095461111300053X?via%3Dihub

7. Operation
Finger is placed in between the light source and
the light detector. Non absorbed light by finger
reaches at detector.
Light is emitted from light sources which goes
across the pulse oximeter probe and reaches the
light detector.

8. Concept of absorbance
Amount of light absorbed is proportional to the concentration of the light
absorbing substance.
Beer’s Law – the absorption of light is proportional to
the concentration of a sample.
Lambert’s Law – absorption is proportional to the
thickness of a sample.
https://www.robots.ox.ac.uk/~neil/teaching/lectures/med_elec/notes6.pdf

9. Absorbance profile
 The oxygenated hemoglobin allows red light to transmit through
and absorbs more infrared light while the deoxygenated
hemoglobin allows infrared to transmit through and absorbs more
red light.
https://www.howequipmentworks.com/pulse_oximeter/

11. Sources of Error
Strength of Arterial Pulse
1:Hypothermia
2: Hypotension
3:Vasopressor use
 Body Movement
Carboxyhemoglobin
Color Interference
Electrocautery(interface with signal)
BP cuff
High intensity light
Venous Pulsations

12. Design and calibration
MAX30101

13. Electrical characteristics

14. Continue….

15. Typical operating characteristics

16. Reflectance based pulse oximeter
INTRODUCTION
 A pulse oximeter is a non-invasive medical device that can
measure the pulse rate and oxygen saturation level in a
person's blood.
 One fundamental property is that oxy Hb absorbs more
infrared light than red light, whereas deoxy Hb absorbs
more red light than infrared light.
 The distance between the light sources and the detector was
examined, as well as the pressure of the reflective pulse
oximeter sensor head onto the skin.
 A reflectance pulse oximeter with circuitry and method for
obtaining the percentage of oxygen saturation is given.
 A microcomputer is used for the signal processing, as
well as the calculation of the oxygen saturation based on the
input light intensity signals.

17. CONTINUE
 Reflectance oximeter suitable for wearable and
 surface-based applications including at the wrist location.
 High quality photoplethysmographic (PPG) data can be
collected.
 Further signal processing is needed to obtain the actual
value of oxygen saturation
 Reflectance type PPG device is developed for the continuous
monitoring of arterial oxygen saturation.
 The result obtained was in good agreement with the finger
PPG.

18. PRINCIPLE OF OPERATION OF
REFLECTIVE OXIMETRY
 The scattering coefficient is much bigger than the absorption
coefficient for most human tissue. Therefore, it is possible
to build a model where the photon movement in the body
tissue can be considered as a diffusion process.
where ;ø(r, t) is the fluence rate, which represents the effective
photon density at the position r and at time t. D denotes a
diffusion coefcient, a represents absorption coefficient of
the tissue and S(r; t) represents the light source.
https://goldbook.iupac.org/html/P/P04635.html

19. Density equation of photon reflected
 The density of the photon reflecting from the body
tissue is determined by the flux of the illumination and the
detected light intensity.
When time is long enough ,the ratio of reflection coefficient
becomes
As a result, the change ratio of reflected light intensity
W= Iac/Idc is proportional to the absorption coefficient of
the tissue. The AC part of the signal represents absorption
of fluctuating wave of pulsing blood, while the DC part
represents absorption of human tissue and vessel

20.  Mathematical equations of sp02 calculations
 Second degree differential equation gives the accurate value

21. SYSTEM DESIGN

22. CONCAVE SENSOR MODULE

23. SIGNAL PROCESSING MODULE

24. Acquired signal by sensors

25. Calibration and calculation of spo2

26. conclusion
It is reflectance based pulse oximeter
The special design of its concave shape helps the
sensor module to stay in the chosen location of the
wrist.
During the calibration process, it is found that a
second-order relationship between the R value and
the oxygen saturation can provide a better t with the
data.

27. Pulse oximeter sensors
https://www.mouser.in/new/maxim-
integrated/maxim-max86140-oximeter/
https://www.maximintegrated.com/en/produ
cts/sensors/MAX30102.html
https://www.digikey.in/en/product-highlight/m/maxim-
integrated/max30101-pulse-oximeter
https://pdfserv.maximintegrated.com/en/an/AN6780.pdf

28. Testing parameter and tool and
acceptance value for pulse oximeter
https://www.flukebiomedical.com/products/biomedical-test-equipment/patient-
monitor-simulators/prosim-spot-light-spo2-pulse-oximeter-analyzer
http://www.mediaidinc.com/Manuals/M300_Manual_English_SM.pdf
https://www.who.int/patientsafety/events/08/1st_pulse_oximetry_meeti
ng_background_doc.pdf
https://www.flukebiomedical.com/sites/default/files/resources/Prosims
pot_ENG_D_W.PDF

29. General software model
 The pulse oximeter demo is based on the Freescale USB stack and behaves as a USB CDC
(Communication Device Class).
 The demo works using state machines that execute one state per cycle avoiding CPU
kidnapping and emulating parallelism.
 https://www.nxp.com/support/developer-resources/evaluation-and-development-boards/tower-
development-boards/mcu-and-processor-modules/kinetis-modules/pulse-oximeter-development-
kit:MED-SPO2

30.  Every state machine is a task that has to be performed by the
MCU. The system can perform several tasks completing one at
time and running the next one until the first one is accomplished
in a FIFO (First In First Out) organization. Some state machines
contain sub-state machines allowing the MCU to distribute the
CPU load equally.
 As mentioned before, software is based on the Freescale USB
Stack with PHDC.
 MED-SPO2 software is basically divided in three main parts:
• Initialization
• Communication with PC
• Measurement Execution

31. THANK YOU