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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