How Does A Pulse Oximeter Work?

Pulse oximeter is used in measuring the level of oxygen carried by the hemoglobin in the entire body. The reading in the oximeter is an important indicator of lung and heart function. The level may be measured by analyzing a blood sample. But for a much quicker, less invasive process, a reading from the finger tip, earlobes or toes through the pulse oximeter can be used.

For each hemoglobin molecule, four oxygen molecules can be carried. Through pulse oximetry, the percentage of oxygen currently carried by the hemoglobin with maximum level of oxygen hemoglobin is able to carry is compared. The percentage is called the oxygen saturation level.

Oxygenated blood leaves the lungs and is then pumped by the heart through the artery. The deoxygenated blood returns to the lungs through the veins to pick up more oxygen from the lungs as the organs use oxygen. The oxygen level of the blood affects how light waves are being absorbed. The blood rich in oxygen absorbs light and lets the red light pass through. The deoxygenated blood absorbs the red light and allows infrared light to pass through. A pulse oximeter emits red and infrared light through the sample site. A light detector on the opposing side measures the light that pass through. It then calculates the ratio of red to infrared light. The ratio will be compared to a scale that is calibrated to each oximeter to assess the oxygen saturation level. The oxygen saturation level in the body of a young and healthy individual has the reading between 95 to 99 percent.

The oxygen saturation levels must be taken the arterial blood rather than from the venous blood, which is oxygen depleted. However, the light emitted by the oximeter has passed through the arteries as well as the veins, skin, bone, and other tissues. All of which affects light absorption. Since the arterial blood is pumped by the heart, it waxes and wanes as the heart beats. The oximeter measures both trough and peak levels of light absorption. The difference in the two levels lies in the light absorbed by the arterial blood. The oxygen saturation levels may be taken at a single time, but this is can be an unreliable reading. More accurate information about the heart and the lung function is gained by taking readings over time and analyzing the trends.

Some factors may lead to false oximetry readings, such as advanced age, irregular or weak heartbeat, cold hands, weak pulse or incorrect placement in the oximeter. Skin color and nail polish will not affect the readings of the pulse oximeter.

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Where Pulse Oximeter Began

A pulse oximeter is one of the most common and convenient medical health devices nowadays that anyone could use anywhere, anytime. Thus, it is an effective method of measuring the blood-oxygen saturation and pulse rate.

It is said that the original pulse oximeter was developed since 1935; it is just a two-wavelength ear saturation meter with red and green filters. This device only measures O2 saturation until it later switched to red and infrared filters. In 1949, some scientist added a pressure capsule to squeeze the blood out of the ear thus, this method is not used clinically because it is hard to implement. Therefore, in 1964, it appears an eight wavelength of light which is absolutely used to read ear oximeter. It is used usually in laboratories due to its size and cost.

The pulse oximeter was developed in 1974 using the ratio of red to infrared light absorption of pulsating components, then it is introduce commercialized in 1981. During that time, it focused mainly on the respiratory care and later on used in operating rooms to monitor oxygen levels. The introduction of oximeter allows continuous measure of patient's oxygenation, through this non-invasive measure, practice of anesthesia improve patient safety.

Operating rooms in 1987 use oximeter for their standard care monitoring, this usage of device rapidly spread throughout hospitals from recovery rooms to various intensive care units. Pulse oximeter device also particular in neonatal units since newly child born do not thrive for inadequate oxygenation; thus, they are blinded with too much oxygen.

In 1995, oximeters could measure not only the pulse rate but also patients' motion and low perfusion which are advisable for those who have sleep disorders. During the development of oximeter, there also appear some portable and in home oximeter devices that are useful for those who need to measure their oxygen saturation and determine their pulse rate.

The latest involvement of oximeter is in 2009, when the first Bluetooth-enable fingertip pulse oximeter was introduced. It enables medical practitioners to monitor patient's pulses and oxygen saturation levels even at distance. It also allows patient to monitor their own health through online access for their health records and data.

Because of the simplicity and speed of oximeter, they are usually of critical importance in emergency medicine and are also very useful for patients with respiratory and cardiac problems; some portable pulse oximeter devices employ software that registers a patient's blood oxygen saturation and pulse rate.

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