With the rapid outbreak of CIVID-19 in the world, the global demand for medical equipment has increased dramatically, especially for invasive ventilators. The blood oxygen saturation concentration is one of the important diagnostic indicators of this new coronavirus, so the demand of the oximeter is also multiplied. The oximeter can be divided into two types. One is the in-hospital equipment used in the hospital, which is generally integrated on the vital signs monitor and obtains the blood oxygen data through the blood oxygen probe; the other is the finger clip type used outside the hospital Oximeter. itsoug also introduced a variety of sensors for use on oximeters.
Pulse Oximeter Test Principle
The oximeter is a non-invasive measuring instrument for blood oxygen saturation (SpO2). Oxygen saturation is defined as the amount of oxygen dissolved in the blood, mainly for the detection of hemoglobin (HbO2) and deoxyhemoglobin (Hb). Two different wavelengths of light are used to measure the difference in absorption spectrum between the two. Blood flow will be affected by the concentration of both, and their absorption coefficient can be measured by red and infrared spectroscopy. HbO2 and Hb have different levels of light absorption at different wavelengths. Deoxyhemoglobin has a strong absorption of red light, while hemoglobin has a strong absorption of infrared light.
Differences in extinction coefficients of HBO2 and HB at different wavelengths / NXP Semiconductors
Oxygenated hemoglobin and reduced hemoglobin have different absorption characteristics in the visible and near-infrared spectrum. Reduced hemoglobin absorbs more red frequency light and absorbs less infrared frequency light; while oxyhemoglobin absorbs less red frequency light , Absorb more infrared frequency light. This difference is the most basic basis of the SpO2 measurement system.
To measure the human body’s absorption of red and infrared light. The red and infrared light-emitting diodes are located as close as possible to each other, and the emitted light can pass through single tissue points in the human body. A single photodiode responding to red and infrared light receives light first, and then a transimpedance amplifier generates a voltage proportional to the received light intensity. Red and infrared LEDs are usually time multiplexed, so they don’t interfere with each other. The ambient light is estimated to be deducted from each red and infrared light. Measurement points include fingers, toes and earlobe.
Pulse oximeters provide a noninvasive method to measure blood oxygen saturation or arterial hemoglobin saturation. The working principle of pulse oximeter is based on the change of light absorption during arterial pulse. Two light sources located in the visible red light spectrum (660 nanometers) and the infrared spectrum (940 nanometers) alternately illuminate the area to be tested (generally fingertips or earlobe). The amount of light absorbed during these pulsations is related to the amount of oxygen in the blood. The microprocessor calculates the ratio of the two spectra absorbed, and compares the result with the saturation value table stored in the memory to obtain the hemorrhagic oxygen saturation.
A typical oximeter sensor has a pair of LEDs that look directly at a photodiode through the translucent part of the patient’s body (usually the fingertip or earlobe). One of the LEDs is red light with a wavelength of 660nm; the other is infrared light with a wavelength of 940nm. The percentage of blood oxygen is calculated by measuring the light of these two wavelengths with different absorption rates passing through the body.
Characteristics And Application Of Special Infrared Emitting Tube For Oximeter
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IRR60-48C / TR8 is an infrared light-emitting diode in a miniature SMD package, molded in a flat-top angle LED water-transparent plastic. The device is a spectral match between a silicon photodiode and a phototransistor; IRR60-48C / TR8 is an ITSOUG professional oximeter, The patch infrared emission tube developed by the sensor is a special infrared emission tube developed for the oximeter. The following are the main parameters!
The testing principles of the oximeter are almost the same. They use red light, infrared LEDs and photodiodes and other photosensitive elements to measure the transmission of fingertips and earlobes. The difference lies in signal processing and filtering, power consumption, and as for data transmission, Bluetooth or WiFi transmission schemes are more or less adopted to adapt to smart wearable products.
