Overview

One of the best methods for monitoring the cardio-pulmonary condition of a patient in a hospital or an athlete in training is the measurement of the subject's blood gases, oxygen and carbon dioxide. The process is invasive and requires the use of an expensive device known as a blood gas analyzer. An alternate method of determining the amount of oxygen in blood is pulse oximetry. This method is easy and non-invasive, and can be performed with a simple device like the PO2-100D Pulse Oximeter (Figure 1) that has a sensor that clips over the end of the subject's finger or toe.

Operating principle

The PO2-100D Pulse Oximeter measures the amount of oxygen in blood indirectly by determining the oxygen saturation level (SpO2) of the hemoglobin in blood. Hemoglobin exists in the blood in two different forms, oxygenated (oxyhemoglobin) and deoxygenated (deoxyhemoglobin). Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass; where as, deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass. Therefore, the absorbance of each wavelength of light depends on the saturation or desaturation of hemoglobin, and can be used to determine the oxygen saturation level of the hemoglobin.

The sensor of the PO2-100D emits wavelengths of light at 600nm (Red) and 925nm (Infrared), and then detects the absorbance of those wavelengths by the hemoglobin in the blood. Through the programming built into the PO2-100D, the absorbance of light at each wavelength is used to determine the ratio between the concentrations of oxygenated and deoxygenated hemoglobin in the blood. After conversion of the output of the PO2-100D to the proper units, the level of oxygen in the blood is expressed as the percentage of oxygen saturation. Normally, the oxygen saturation level of blood is between 95 and 100%.


PO2-100D Pulse Oximeter connected to an IX/214 data acquisition unit - Resulting curves in Labscribe