Clinical application of PPG

1. Waveform characteristics of PPG

The collected PPG waveform is composed of AC and DC, and the frequency of the AC part is about 1HZ, which is determined by the heart rate. The DC component changes very slowly and is determined by respiration, vasoconstriction, and THM waves, all of which are determined by human conditions.

Different people have different situations. The DC and AC components can be derived using suitable filtering and amplification. available for our clinical use.

2. Measurement of LED light source and PPG waveform

The process of LED light source passing through blood vessels and tissues is relatively complicated, mainly including reflection, refraction, scattering, and fluorescence. Blood flow, vessel wall motion, red blood cell orientation, tissue fluid, etc. will affect the acquisition of PPG signals.

There is a direct relationship between PPG pulse waveform and blood flow perfusion. Large blood flow can receive less light. Quantitative analysis has been under constant analysis and research.

The wavelength of the emission signal of is very important for the detection of biological tissue components. Human tissue has an optical water window effect. Water has a very strong ability to absorb ultraviolet and long infrared waves, and short wavelengths are strongly absorbed by black. In the absorption spectrum of water, visible light (red light) and near-infrared light are easy to pass through. Therefore, red light and near-infrared light are more common as the measurement light source. The reduction of HbO2 and Hb is manifested at a certain wavelength, in order to measure the performance over a certain wavelength range. For optical radiation intensity, the wavelength of operation determines the depth of penetration into human tissue.

PPG is our main method for in-depth study of the components in tissue fluid, and it is used together to complete our clinical data collection.

3. PPG measurement tools

LED light source, converts electrical energy into bit light energy, LED is small, has a long life, wide temperature range, and small change in peak radiation wavelength.

PPG single-point test, ears, fingers, toes, easy detection of pulses, pulse amplification and photoelectric matching, near-infrared CCD mage system, very intuitive for the perfusion of physiological tissue fluids. The multi-wavelength PPG imaging system can analyze the arterial oxygen saturation and distribution inside the tissue. Tissue oxygen levels can be important in many medical diagnoses. A certain standard ratio of red light and near-infrared light can monitor blood oxygen saturation. There are also other tissue fluid components under constant testing.

4. PPG measurement signal processing and reproducibility

   Bilateral measurement is better, but in terms of hardware cost and software complexity.

5. Clinical application

• Blood oxygen
  The red and near-infrared AC signal amplitudes are sensitive to changes in blood oxygen because different trophic and non-trophic erythrocytes absorb light differently.
•  Heart rate
• The number of pulses in the PPG is the heart rate. ECG and PPG to determine heart rate with 92%-97% accuracy.
•  Blood pressure
• Sophisticated algorithms for blood pressure.
•  Cardiac output

     6.  liters of blood a minute, there are many complex and model flow methods.

 Breathing
The respiration-induced intensity change (RIIV) in the signal is affected by the return to the heart in the veins.

7. Blood Photoelectric Evaluation

Detection of disease is because peripheral pulses are often attenuated and delayed due to the severity of cardiovascular disease. Many properties can be used to detect disease. Rising edge, frequency characteristics, aspect ratio, amplitude, and waveform, etc. As a result, many of our applications are based on the data collection, and then the combination of algorithms, big data, machine learning, and artificial intelligence has realized our digital health plan.

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