With Circular, anybody can benefit from a preventive tracking of respiratory problems and checking your blood oxygenation might just help you with that.

How does it work?

When oxygen is inhaled into the lungs it attaches to a protein in red blood cells called hemoglobin. The red blood cells transport the oxygen into the bloodstream and flow through pulmonary veins, then into the left atrium and left ventricle, and finally circulates throughout the body’s organs and their cells. 

In order to know how much oxygen is in your blood, the sensor at the bottom of your ring emits red and infrared light. While passing through your finger, the light hits your blood cells and is absorbed differently by the hemoglobin without oxygen (deoxyhemoglobin) than by the hemoglobin with oxygen (oxyhemoglobin) because of their concentration and resistance to light. The calculated rate is expressed as a percentage and a normal reading ranges from 94 percent to 100 percent.

Circular’s readings are accurate and provide results within a 2-percent difference either way of what it truly is. If your reading was 90 percent, your true oxygen saturation level may be anywhere between 88 and 92 percent. You should also keep in mind that external factors such as movement and temperature can impact the accuracy and that you should always consider your reference and personal feeling as a primary assessment. Use your blood saturation as a tool.

We will first discuss how to interpret your readings for your wellness, and then discuss how it might help you.

Spo2 for health and prevention

Pulse oximetry is a method doctors use for rapid assessment and monitoring of a patient’s respiratory function. It may be used to monitor the health of individuals with any type of condition that can affect blood oxygen levels, especially while they’re in the hospital. But let's leave this work to the doctors.

SpO2 for Sleep apnea evaluation 

You might correlate blood oxygenation to sleep apnea events (sleep disorder in which breathing repeatedly stops and starts). The good news is that it can be a great indicator and reflects these events well. 

There is around a twenty-second delay after the onset of the cessation of nasal airflow. The measurement of SpO2 level is useful for screening suspected sleep apnea events, but it might not be able to provide live and precise occurrences. Best practice would be to check your readings in the mornings by keeping in mind these simple facts: less than 5 sleep apnea events an hour is considered normal. You might want to check with your doctor if that exceeds 15. Look for sudden drops in the graph. 

Associated symptoms may be: frequent morning headaches, swelling in ankles and feet (edema), tiredness, shortness of breath, irregular heartbeats rhythms, high blood pressure,

lightheadedness, dizziness, skin and nail beds may turn bluish in color (cyanosis), confusion, memory loss, higher red blood cell count in blood (polycythemia).

SpO2 for Recovery

Oxygen saturation is a key factor in performance if you live or train at altitude, or tend to overtrain. Using SpO2 readings with your usual training metrics can, first and foremost, help you gauge whether you’re recovering properly.

An athlete that wakes up feeling “not right” after a hard training block and a poor night of sleep will tend to see his SpO2 reading lower than his baseline. In this case you may feel well enough to go train, but your poor sleep and low SpO2 corroborate your sense of “not feeling right.” In that case, instead of training as planned, you should focus on recovery and sleep more for the next days. Subsequently, your SpO2 will normalize and the following training days should go very well.

Correlate your RHR, HRV, RR, and SpO2 after training days to see where your recovery is. Paying attention to the right numbers can result in a good training block and help avoid an over-training.

SpO2 for Altitude Acclimatization

At altitude, where the air is thinner, it is more difficult for your body to get adequate oxygen to your muscles and tissues. For example, if you’re racing or training at 10,000 feet (3000 m), the amount of effective oxygen in the air is about 15 percent (compared to 21 percent at sea level). If you’re used to living at sea level, this change in oxygen availability will kick off a cascade of physiological adaptations, some of which are advantageous no matter where you’re racing.

To start, there will be an increase in your breathing and heart rates; and the volume of blood ejected from the heart (stroke volume) will be reduced. Over your first 24-48 hours at altitude, blood plasma volume will also be reduced to improve the oxygen-carrying capacity of your blood by volume. These adaptations won’t necessarily feel good, in fact, you’ll probably feel like you’re doing more work for less reward.

In the first couple of days at altitude, you want to see a lower SpO2 and an elevated heart rate (HR) and breathing rate (BR). This is your body attempting to balance out the lack of oxygen in the air by moving it faster through your body.

With prolonged stays at altitude, most people’s SpO2 will stay about the same or increase slightly; but your heart and breathing rates should normalize, as well as your ability to perform an exercise at altitude. A SpO2 of 88 to 92 percent will give you the most beneficial training adaptations without causing undue fatigue.

That means you’ll be able to race and train as normal at altitude, and will likely enjoy some extra endurance at sea level.‍

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We remind you that the Circular™ ring is not a medical device and should not be used to diagnose or monitor a pathology.

Scientific sources:

• Comparison of SpO2 values from different fingers of the hands, Springerplus.Gokcen Basaranoglu, Mefkur Bakan,Tarik Umutoglu, Seniyye Ulgen Zengin, Kadir Idin, and Ziya Salihoglu. 2015.
• Pulse oximetry. Crit Care. Amal Jubran. 2015.
• Sleep apnea and oxygen saturation in adults at 2640 m above sea level. Sleep Science. Maria Angelica Bazurto Zapata, Elida Duenas-Meza Dario Maldonado Gomez Claudia Jaramillo, Carlos Torres-Duque. June 2014.
• Usefulness of Pulse Oximeter That Can Measure SpO2 to One-Digit After Decimal Point. Yonago Acta Med. Akihiro Yamamoto, Naoto Burioka, Aritoshi Eto,Takashi Amisaki,and Eiji Shimizu. 2017 Jun.