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February 4, 2019

How does pulse oximetry work

The amount of oxygen your blood delivers throughout your body is crucial for sleep quality and your health in general, and healthy blood oxygen levels during sleep is dependent upon your quality of breathing. If you’re one of 54 million people in the United States with sleep apnea, your oxygen intake is being disrupted, which can lead to a multitude of health issues.

What is pulse oximetry?

Pulse oximetry is a noninvasive and painless test that measures the oxygen level in your blood (or your oxygen saturation level). It quickly detects even small changes in how efficiently oxygen is being carried to the extremities furthest from the heart, including the legs and the arms.

A pulse oximeter is a small device that clips on a body part, like a finger, a toe, an earlobe and the forehead. It’s often used in a critical care setting like an emergency room or a hospital, and some doctors may use it in office as part of a routine checkup.

Once the pulse oximeter is attached to a body part, small beams of light pass through the blood measuring the amount of oxygen. It does this by measuring changes of light absorption in oxygenated or deoxygenated blood. A pulse oximeter will tell you your oxygen saturation levels along with your heart rate.

When breathing becomes disrupted during sleep (called a stopped breathing event or SBE), as may occur in obstructive sleep apnea, the oxygen levels of the blood may repeatedly fall. Prolonged drops in oxygen levels during sleep are known to lead to a variety of health complications like depression, heart disease, high blood pressure, diabetes and more.



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Why might I need pulse oximetry?

There are many situations where your doctor will want to measure your blood oxygen level, including:

  • During or after surgery or procedures that use sedation
  • To check a person’s ability to handle increased activity levels
  • To check if a person has moments when breathing stops during sleep (sleep apnea)

Pulse oximetry is also used to check the health of a person with any condition that affects blood oxygen levels, such as heart attack, heart failure, chronic obstructive pulmonary disease (COPD), anemia, lung cancer and asthma.

Pulse oximetry and sleep apnea

If you are being tested for sleep apnea, a sleep doctor will use pulse oximetry during a sleep study to evaluate how often you stop breathing during the night. The pulse oximeter contains a red light sensor that shines through the surface of your skin to measure your pulse (or heart rate) and the oxygen content of your blood. The oxygen level in your blood is measured by color: highly oxygenated blood is more red, while blood that is low in oxygen is more blue. This changes the frequency of the light wavelength that is reflected back to the sensor. These data are recorded throughout the night of your sleep test and are recorded on a graph. Your sleep doctor will review the graph at the conclusion of your sleep test to determine if there were abnormal drops in your oxygen level during your sleep test. If you have frequent dips in blood oxygenation, it’s very likely you have sleep apnea.

What is a good oxygen level during sleep?

An oxygen saturation level over 95 percent is considered normal. Anything below 92 percent oxygen in your blood may be a sign that you have breathing problems during sleep, which could mean you have sleep apnea or another disorder like severe snoring, COPD or asthma. However, it’s important for your doctor to understand how much time you spent with oxygen saturation below 92 percent.There can be drops in oxygen levels that are not long enough or low enough to be called abnormal or unhealthy for your body. For example, a couple of seconds with 80 percent oxygen saturation for two times in one night may not be a reason for concern.

If you want to discover your blood oxygen levels during your sleep, you could go to a sleep lab to have an overnight sleep study, or you can use a monitor at home.

The pulse oximeter can be a very useful medical device for sleep apnea patients. It's much cheaper than a sleep study, and it can reveal important information about your sleep quality or how effective is your sleep apnea treatment.