pulse oximeter

What is a Pulse Oximeter and What Does it Measure?

Living with lung disease such as COPD, emphysema, and lung fibrosis can be a struggle. However, you can live an enjoyable life filled with quality by following a simple, daily routine that includes good self-care. If you require oxygen, there are portable and stationary systems to meet your oxygen needs, which can minimize the inconvenience associated with oxygen therapy. In this article, we describe and demonstrate how a pulse oximeter can be used to measure your oxygen level, to adjust your oxygen setting, and to inform your doctor of a change in your condition. In addition, the pulse oximeter can be used as a biofeedback training device along with pursed lips breathing to increase your oxygen level.

Why do we need Oxygen?

Your need for oxygen is continuous. The human body requires oxygen, food, and water to create energy and fuel our active lives. Oxygen has to be brought in from the outside air and carried to each and every cell each and every minute.

This is a continuous path of transport systems. Your lungs deliver oxygen into your bloodstream; your heart pumps the blood to the tissues where oxygen is delivered to every cell. Each cell has a manufacturing system called mitochondria that uses oxygen and food to create energy for the muscles to power the body. Carbon dioxide, the waste product of this process, is expelled.

Every tissue of your body requires oxygen constantly to create the energy of life. There is plenty of oxygen in the atmosphere to meet the needs of people with normal lungs. However, if you have lung disease, you may need extra oxygen to meet your body’s oxygen requirements. You may have been diagnosed with COPD or lung fibrosis. COPD is the combination of bronchitis, asthma, and emphysema, while lung fibrosis is the build-up of scar tissue that impedes the transfer of oxygen across the alveolar-capillary membrane.

Determining Your Need for Oxygen

Your doctor will prescribe oxygen based on the level of oxygen in your bloodstream during rest, exertion, and sleep. Oximetry is the most convenient method of testing your oxygen level.

Your oximeter tells how much of your blood is filled with oxygen. Your SpO2 oximetry reading is an important piece of information, but it does not stand alone. Combined with other information, you and your doctor can make important decisions to guide your self-management program.

How Your Body Gathers Oxygen

The diaphragm pulls down and the chest muscles pull out to lengthen and widen the chest to make room for air to enter the lungs. Oxygen in the air reaches the expanding alveoli or air sacs where a network of tiny blood vessels called capillaries receives the oxygen as it diffuses across the alveolar-capillary membrane. At the same time, carbon dioxide, which is produced in the body cells and carried on the hemoglobin molecule of the red blood cell, detaches and diffuses across the alveolar-capillary membrane to be exhaled to the atmosphere. Once in the blood, oxygen quickly attaches to the hemoglobin molecule of the red blood cell turning it red.

Freshly oxygenated blood is pumped by the heart through the major arteries towards the vital organs, muscles, and nether reaches, delivering oxygen to each and every cell. Once inside the cell, oxygen finds its way to the mitochondria, which uses the oxygen to create energy.

Carbon dioxide, the end product of the body’s metabolism, is carried by the bloodstream to the lungs where it’s exhaled to the atmosphere thus completing one of millions of cycles that sustain life.

Measuring your oxygen level with a pulse oximeter

As your red blood cell gathers oxygen onto the hemoglobin molecule, it turns red. Redness of the blood is the base of Oximetry. As the blood’s capacity to contain oxygen becomes filled, the blood turns more red.

The oximeter functions by shining two lights, red and infrared, through your finger. Sensors on the other side of your finger detect how much of each light is passing through. The red light measures unoxygenated hemoglobin, whereas the infrared light measures oxygenated hemoglobin.

A tiny computer inside the oximeter compares the two lights and displays a number on the screen that tells the percentage of hemoglobin saturation with oxygen. The oximeter takes its reading at the peak of the pulse where the blood contains the most oxygen. At any other point on the pulse, there is less oxygenated blood causing an inaccurate reading. Thus, it is imperative to make sure that the oximeter is detecting regular pulses. Now, most oximeters have either a display or a pulse indicator that informs you of regular pulses. The normal oxygen level is about 95% to 97% at sea level, but 90% is just barely acceptable.

Pulse oximeter compared to ABGs (Arterial blood gas)

Arterial blood gases measure your oxygen level by drawing blood from your artery. It is the most accurate measurement of your oxygen level, and it also measures your carbon dioxide and provides other useful information. On the downside, it is invasive, it involves a needle stick, and it measures only a single point in time. Oximetry measures only oxygen, but it does so non-invasively and continuously.

Advantages of pulse oximeter

It is non-invasive, inexpensive, and useful during exercise and sleep. Patients can use it at home or anywhere, and can use it to learn how to increase their oxygen level.

Position the pulse oximeter clip on your finger, keeping your finger steady. Wait for a strong and steady pulse and consistent SpO2, and then take your reading.

Things to avoid while using a pulse oximeter

Avoid dark nail polish or artificial nails. Don’t tighten your hand as it may cut off the circulation to your finger. Avoid excessive movement of your finger that might give a false reading.

Here are some suggestions. If the pulse is weak, try running warm water over your hand to increase the blood flow or reposition the pulse oximeter. During exercise, try to steady your finger before taking the reading. Relax your hand to maximize blood flow. An important point, there’s a lag time for any change in your blood oxygen to reach your finger, so be sure to wait for 20 to 30 seconds before taking your final reading.

Oximetry during Exercise

If you have lung disease, daily exercise, such as walking, is an important part of maintaining your health. Exercise is essential to active living. Whether you exercise or simply move around, you raise your body’s metabolism. Consequently, you require more oxygen when you are active. Your doctor will determine your oxygen need during exercise. Your pulse oximeter will let you know if your oxygen level is adequate during exercise or activity.

When you exercise, bodily movement may cause false oximetry readings, therefore, try keeping your finger steady when taking the reading. Make sure that the pulse oximeter is showing a strong and regular pulse. Exercising bodies require more oxygen. When you increase your activity, your oxygen level may drop, therefore, your resting oxygen setting may be inadequate to meet your body’s needs during exercise. That saturation drop is the reason which stops you from exercising. In order to detect the lower oxygen level, keep reading the pulse oximeter for about 30 seconds after you stop exercising. Your saturation may continue to drop.

Report low oxygen readings to your doctor and get instructions on adjusting your oxygen setting during exercise. It’s important that you are able to maintain adequate oxygen levels during exercise.

Oxygen for Air Travel

Airplanes are pressurized to 5000 to 8000 feet, and sometimes higher, not to sea level. This is equivalent to Denver’s Altitude, or even higher. If you need oxygen on the ground, you will definitely need oxygen during air flight. Sometimes you don’t require oxygen on the ground, but do need oxygen during air flight. Your doctor will make that determination.

Make sure that you plan your travel at least two to three weeks ahead of time, and inform the airline that you will be requiring oxygen. Each airline has its own set of procedures for oxygen.

You can buy oxygen from the airline. However, it is better to run a portable oxygen concentrator from your oxygen supplier. Your doctor will write an oxygen prescription, a copy of which will go to the airline and another copy will go to your oxygen company. On the flight, your oximeter will tell you if your oxygen setting is adequate.

How to Increase Your Arterial Oxygen

In pulmonary rehabilitation, there is a breathing technique called Pursed Lips Breathing, which can increase your oxygen level. Breathe in through your nose and exhale slowly through your mouth while pursing your lips. Think of it this way. Smell the roses and gently blow the candle causing the flame to flicker, in through your nose and out through pursed lips.

If you use your pulse oximeter as a guide while doing pursed lips breathing, you can learn to raise your oxygen level by as much as three to four points. Just focus on the oximeter while doing pursed lips breathing. If you are successful, your oxygen level will increase.

Pursed lips breathing with oximetry is especially useful when active and exercising. It is important to remember that it takes time for the blood to travel from your lungs to your finger oximeter, so wait for about 20 seconds to determine if there is a change in your oximetry reading. Be persistent. Practice makes perfect.

Reporting to Your Doctor

Control over your lung disease is determined by how you manage at home. Taking your medication and oxygen properly, keeping your airways clear, exercising, and monitoring for an infection or a flare-up of your illness will all make a major difference on how your lung disease affects you.

When there is any change in your condition, it is crucial that you call your doctor. Some doctors provide their patients with a rapid action plan to initiate in case of signs or symptoms of an infection. The signs are more shortness of breath, cough with sputum, and a change in your oximetry reading. And these may signal an infection, a flare-up, at which time, you may need antibiotics, Prednisone, and inhalers, as well as a change in your oxygen setting. Your doctor will determine and prescribe this.


It is essential for you to obtain a quality oximeter and use it correctly. Your oxygen needs are greater when you are active, exercising at higher altitudes, or up in an airplane, therefore, you should monitor your oximetry during each of these conditions. A change in your oximetry level may signal a change in your condition or even a flare up and a need to call your doctor. Practice your pursed lip breathing with your pulse oximeter as a guide to increase your oxygen level. Use your oximeter in good health and as directed by your doctor.

Published by

Dr. Aleksandar Grbovic

Hi! My name is Aleksandar Grbovic. I’m a radiology resident with five years of experience in General Medicine. As a medical writer, I have only one goal in my mind - to bridge the gap between doctors and patients point of view by breaking down complex medical topics and presenting them in lay people language. Knowing that my writing might help someone out there connect the dots is what keeps me motivated.

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