Pulse Oximeter(脉搏血氧仪）

Pulse Oximeter(脉搏血氧仪）

Table of Contents
 

Chapter 1: Introduction................................................1

Chapter 2:Block Diagram Explanation................................................2

 

Chapter 1:Introduction

Biomedical Instrumentation is an application of Biomedical Engineering that focuses on the instruments and mechanics utilized to compute, assess and serve the biological systems. Various biomedical instruments are utilized in the medical sector for treatment or diagnosis purposes. Biomedical instruments make use of multiple sensors to monitor the physiological parameters of a human being.
Nowadays with the aid of Artificial Intelligence (AI), machines and humans are able to communicate with each other. The branches such as Machine Learning (ML) and Deep Learning (DL) are contributing a lot for making the intelligent healthcare or medical sectors. The best example is that machines like robots are able to perform the operations or surgery without the assistance of a doctor or physician.
A pulse oximeter is a device that determines the oxygen saturation of a patient’s blood using a sensor.It yields a computerized readout and sounds an alarm if the blood saturation becomes less than optimal.

 

Chapter 2:Block Diagram Explanation

 sensor:

 

Function:

• Light-Emitting diodes(LEDs) that emit light at two different wavelengths: red and infrared (IR).
•  A photodetector that captures the light transmitted through or reflected by the tissue.
•  LEDs provide the light sources at specific wavelengths,while the photodetector converts the light signal into an electrical signal.

Biochemistry

•  Different absorption spectra of oxygenated and deoxygenated hemoglobin.
• Oxygenated hemoglobin absorbs more infrared light and less red light,deoxygenated hemoglobin absorbs more red light and less infrared light.

 

Modulator (Red and IR)

 Function

•  Modulates the red and infrared LEDs,ensuring they emit light in a controlled manner.
• Help in distinguishing the signals corresponding to red and IR light.

Electronic Circuits & system

•  Ensures that the LEDs emit light alternately.
• Modulation frequency helps in separating the signals and reducing noise.

 

Amplifier

 Function

The weak signal detected by the photodetector is amplified to a level suitable for further processing.

Electronic Circuits & Systems

Amplifiers increase the signal strength,making it easier to process and analyze.This is crucial for maintaining signal integrity and ensuring accurate measurements.

 

Demultiplexer

 Function

The demultiplexer separates the signals corresponding to the red and infrared light.
 

Electronic Circuits & Systems

By separating the red and infrared signals,the demultiplexer allows for individual processing of each signal,which is essential for accurate calculation of oxygen saturation levels.
 

Bandpass Filter

Function

The bandpass filters isolate the AC (pulsatile) and DC (non-pulsatile) components of the signal for both red and infrared channels.
 

Electronic Circuits & System

Filters remove noise and isolate relevant signal components.The AC component represents the pulsatile part caused by the heartbeat, while the DC component represents the non-pulsatile baseline signal.

 

Amplifiers (Amp) 

 

Function

Further amplify the AC components of both red and IR signals.

Electronic Circuits & Systems

•  AC components of the red and IR signals: the pulsatile part of the signal caused by the heartbeat.
• Additional amplification: ensure that these signals are strong enough for precise analysis.
• Enhances the signal quality: easier to distinguish between the pulsatile (AC) component and any noise or baseline drift.

 

Analog To Digital Converter (ADC)

 Function

Convert the analog signals into digital signals
 

Electronic Circuits & Systems

• Convert the continuous analog signals (vary over time) into discrete digital signals (series of binary values).
• Digital signals can be processed by digital systems,such as microprocessors, with greater accuracy and flexibility

Microprocessor

Function

Analyze the digital signals to compute oxygen saturation (SpO2) and pulse rate.
 

Microprocessor / signal Processing

• Digital signal processing techniques to analyze digitized signals from ADC.
•  ADC’s resolution (number of bits) determines the precision of the digital representation of the analog signal.

Oxygen Saturation Calculation

• Calculates ratio of the pulsatile components (AC) of the red and infrared signals.
• Ratio to determine (SpO2): oxygenated hemoglobin absorbs more infrared +less red light.

Pulse Rate Calculation

•  Identifies the frequency of the pulsatile component in the signal,which corresponds to the heart rate.

Biophysics / Biochemistry SpO2 calculation

• Principles of spectrophotometry (different substances absorb light at different wavelengths)
• Distinct absorption spectra = able to differentiate based on the ratio of absorbed red and infrared light.