How does a Pulse Oximeter Work?

Whether you are ill, experiencing a medical emergency or the victim of an accident, the first thing a nurse will do is slip what looks like a small clip on one of your fingers to gather two pieces of information - your heart rate and your blood oxygen level. Turns out, these pieces of information will define the first few minutes of your interaction with a doctor or nurse. If both are good, you can receive further diagnostic testing to determine what, if anything, is wrong. If one or both is not within normal limits, your health care team must do everything in their power to stabilize both before continuing to treat any other injuries or illnesses. This clip is called a pulse oximeter and within seconds can answer two questions. Is your heart beating? If so, how fast or slow? Are you breathing? If so, what is your oxygen saturation?

What are the 2 readings on a pulse oximeter
Basic Fingertip Pulse Oximeter

What is oxygen saturation?

Before you can really understand how a pulse oximeter works, you have to understand what it is measuring. Oxygen is vital to life. Every organ, muscle, nerve, and tissue in the body needs oxygen to function the way it should. However, for oxygen to be used by the body, it must travel from the lungs to the intended destination via hemoglobin, or red blood cells. If half of your hemoglobin cells are carrying oxygen, your oxygen saturation is 50 percent. If all of them are carrying oxygen, your oxygen saturation is 100 percent.

How a pulse oximeter measures oxygen saturation

How does a pulse oximeter work

Masimo RAD 8 Pulse Oximeter

The typical pulse oximeter looks like a computerized clip that fits on your finger. Inside this clip are a light source and a light detector that work in conjunction with a computer to determine your body's oxygen saturation. The light source emits a red light and infrared light, and the light detector senses how much of each light is absorbed and how much is allowed to pass through the finger (or toe or ear lobe). As it turns out, oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. On the other hand, deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through. The ratio of red light to infrared light that is absorbed by the body on its way from the light source to the light sensor is your oxygen saturation.

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Nonin Onyx Vantage 9590 Finger Pulse Oximeter

The Pulse Factor

Blood is not stagnant in your veins. Instead, with every heartbeat, your blood travels too and from your extremities where your oxygen levels are often tested. However, rather than trying to pulse red and infrared light through your finger and hopefully capture a reading timed perfectly with your heart rate, the pulse oximeter emits a constant stream of light. It must, therefore, calculate the "changing absorbance" in your finger - the light absorbance that happens with every heartbeat. That is why a pulse oximeter produces two readings - your pulse rate and your oxygen absorption.

For more information on which pulse oximeter is right for you, contact one of our equipment experts who can guide you through the purchase process.