Oxygen Saturation Detector in Blood

Oximetry is the measurement of oxygen saturation in blood, and is usually expressed as a percentage (a normal reading is typically 97 percent or higher). A pulse oximeter is a non-invasive device that measures the oxygen saturation of a person’s blood as well as their heart rate. Pulse oximeters are easily recognized by their associated clip-type probe, which is typically applied to a patient’s finger.

A pulse oximeter can be a stand-alone device, part of a patient-monitoring system, or integrated into a wearable fitness tracker.

The HEXIWEAR consists of a in-built heart rate sensor/pulse oximeter called as MAX30101 that can be used to measure the amount of oxygen saturation (SPO2) or heart rate(bpm).

Blood oxygen saturation

Blood oxygen saturation is measured by examining hemoglobin, which is the oxygen-carrying pigment of red blood cells that gives them their red color and serves to convey oxygen to the tissues. Hemoglobin is found in two forms. The first is called oxidized (oxy-) hemoglobin, which is denoted as HbO2 (also called “oxygen-loaded”). The second is called reduced-oxygen (deoxy-) hemoglobin, which is denoted as Hb (“oxygen-depleted”).

Blood oxygen saturation (SpO2) is the ratio of oxy-hemoglobin to deoxy-hemoglobin. This can also be expressed as: SpO2=HbO2/(Hb + HbO2).

Hb absorbs more (and reflects less) visible red light. HbO2 absorbs more (and reflects less) infrared light. Since blood oxygen saturation can be determined by comparing the values of Hb and HbO2.

The pulse rate can be calculated based on the pulse oximeter’s Analog-to-Digital Converter (ADC) sample number and sampling rate.The SpO2 can be determined using the ratio value(Ratio = (Red_AC_Vrms/Red_DC) / (IR_AC_Vrms/IR_DC).) and a look-up table that is made up of empirical formulas.