subject: What Is A Pulse Oximeter? [print this page] A pulse oximeter is a device used in the medical field to monitor the oxygen content of the patient's blood indirectly, as well as to monitor the changes on the blood volume in the skin. It is often plugged in to a medical monitor, producing a photoplethysmograph, so the medic can see the oxygenation of the patient at all times. Most monitors connected to the oximeter also display the heart rate. There are also portable pulse oximeters operated by battery for monitoring of blood-oxygen in homes.
The first oximeter was manufactured in the 1940's. The first modern pulse oximeter, on the other hand, was developed in the year 1972, using the concept of getting the ratio of red to infrared light absorption of pulsating components at the measured area. It was mass produced and gained popularity in the 1980's.
The blood-oxygen monitor attached to the oximeter displays the percentage of the hemoglobin found in the arteries within the oxyhemoglobin configuration. Normal percentage of the arterial hemoglobin ranges from ninety five to one hundred percent, although below ninety percent is still acceptable. For a patient breathing air at sea level, an approximation of the arterial hemoglobin can be determined from the blood-oxygen monitor reading.
The monitored signal bounces along with the heartbeat due to the expansion and contraction of the arterial blood vessels with each heartbeat. By examining the just varying part of the absorption spectrum, a monitor can ignore the other tissues or polished nails, even though black nail polish can alter readings, and recognize only the absorption caused by the blood in the arteries. Therefore, the detection of the pulse is important to the oximeter's operation, and it will not function at all if there is none.
A pulse oximeter is a convenient non intrusive measuring device. Usually, it has a pair of small light-emitting diodes facing a photodiode through a translucent part of the patient's body, which is typically a fingertip or an earlove. One LED is read, with a wavelength of 660 nanometers, while the other is 905, 910 or 940-nanometer infrared. Absorption at these wavelengths varies considerably between oxyhemoglobin and its deoxygenated form. Thus, the oxyhemoglobin and deoxyhemoglobin ratio can be measured from the ratio of the absorption of the red and infrared light. The absorbtion of oxyhemoglobin and deoxyhemoglobin is practically the same, called the isosbestic point. Earlier oximeters used the wavelengths of 590 and 805 nanometers for correction of the concentration of hemoglobin.
