How an oximeter works

15/06/2022
How an oximeter works

The original oximeter was developed by Millikan in the 1940s. It monitors the ratio of oxygen-carrying hemoglobin to oxygen-free hemoglobin in arteries. A typical oximeter has two LEDs. The two LEDs face the part of the patient to be tested - usually the fingertip or earlobe. One diode emits a beam with a wavelength of 660 nanometers and the other emits 905, 910 or 940 nanometers. Oxygenated hemoglobin absorbs these two wavelengths very differently than without oxygen. Using this property, the ratio of the two hemoglobins can be calculated. The procedure for the test usually does not require blood to be drawn from the patient. A normal oximeter can also display the patient's pulse. According to the Beer-Lambert law, the functional relationship between the ratio R/IR and arterial oxygen saturation (SaO2) should be linear, but because biological tissue is a complex optical system with strong scattering, weak absorption and anisotropy [2- 4], does not fully comply with the classical Beer-Lambert law, thus leading to the establishment of a mathematical model expressing the relationship between the measured value of the relative change of red and infrared light absorbance (R/IR value) and arterial oxygen saturation (SaO2). difficulty. The corresponding relationship between R/IR and SaO2, that is, the calibration curve, can only be determined experimentally. Most pulse oximeter manufacturers use experimental methods to obtain empirical calibration curves to complete the pre-calibration of the products before leaving the factory.




Saturation representation method
Functional saturation: (functional saturation)
SO2=oxyhemoglobin/(oxyhemoglobin+reduced hemoglobin)
Natural saturation: (fractional saturation)
SO2=oxyhemoglobin/(oxyhemoglobin+reduced hemoglobin+carboxyhemoglobin+methemoglobin)
Clinically, functional saturation is often used to reflect changes in blood oxygen content.

cause of saturation drop
Diseases of the respiratory and circulatory systems, disorders of the body's automatic regulation caused by anesthesia, major surgical trauma, injuries caused by other treatments and examinations
Symptoms: Dizziness, weakness, vomiting, and in severe cases, life-threatening.

Evaluation of test results
From medical analysis, the oxygen content in the blood is greater than or equal to 95, which is a normal indicator; the pulse per minute is between 60-100 times, which is a normal indicator. If the values ​​you have detected do not meet the above two indicators, please test 2-3 times at different time points, and keep continuous testing for 2-3 days. If the values ​​still do not meet the standards, it is recommended that you go to the hospital for detailed treatment.