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Oxygen saturation and ODI in sleep
Oct 13, 2020

Von: Fynn S.

If you want to know more about your sleep and quality of sleep, you can’t get past these two terms – oxygen saturation and THE ODI. What do these two terms mean and how do they help me better understand my sleep?

Oxygen saturation

CIRCUL Sleep Tracker with App
The CIRCUL sleep tracker ring measures oxygen saturation, pulse and ODI continuous

Oxygen saturation, also known as SpO2, is a measure of the amount of oxygen-containing hemoglobin in the blood in relation to the amount of non-oxygenated hemoglobin. The body needs a certain level of oxygen in the blood, otherwise it does not function as efficiently. In fact, very low SpO2 levels can lead to very serious symptoms. This condition is called hypoxemia. There is a visible effect on the skin, which is called cyanosis due to its blue (cyan-colored) coloration. Hypoxemia (low oxygen concentration in the blood) can become hypoxia (low oxygen concentration in the tissue).

How the body maintains normal SpO2values

It is essential to maintain normal oxygen saturation levels to prevent hypoxia. Fortunately, the body usually does this by itself. The most important way the body maintains healthy SpO2 levels is breathing. The lungs absorb the inhaled oxygen and bind it to hemoglobin, which then travels through the body with the payload of oxygen. The body’s oxygen demand increases at times of high physiological stress (e.g. when lifting weights or running) and at higher altitudes. The body is usually able to adapt to these increases, provided they are not too extreme.

Normal SPO2 values

In a healthy person, oxygen saturation should be between 95% and 99%.
Anything between 90% and 95% is not dangerous, but if the oxygen saturation is permanently in this area, this usually indicates a health problem. Causes are mostly respiratory, i.e. a problem with breathing or the lungs.
Anything under 90% is critical and should be taken seriously. It can happen during sleep that a desaturation occurs, but SpO2 values below 90% must not be permanent under any circumstances.

SpO2 Values State
Over 95%Very good
93% – 95%These values are fine in the short term, but should not be permanent
90% – 93%These values should be looked at more closely. Under no circumstances must these values be permanent
Less than 90%Critical values! A doctor should be consulted.

Measurement of oxygen saturation

There are many ways the blood can be tested to ensure it contains normal oxygen levels. The most common method is the use of a pulse oximeter to measure the SpO2 values in the blood. Pulse oximeters are relatively easy to use and common in health facilities and at home.

To use a pulse oximeter, simply put it on your finger. A percentage appears on the screen. This percentage should be between 94 percent and 100 percent, indicating a healthy hemoglobin level that transports oxygen through the blood. If this is less than 90 percent, you should consult a doctor.

How pulse oximeters measure oxygen in the blood

Pulse oximeters have been in use for many years. Until recently, however, they were mainly used by health institutions. Now that they are widespread in the home, many people are wondering how they work. Pulse oximeters work by using light sensors to detect how much blood oxygen is transported and how much blood is not transported. Oxygen-saturated hemoglobin is darker for the naked eye than hemoglobin not saturated with oxygen, and this phenomenon allows the highly sensitive sensors of the pulse oxymeter to detect and convert the smallest fluctuations in the blood into a measurement.

What is the ODI

CIRCUL Sleep Tracker Ring App
A sleep report with the CIRCUL sleep tracker ring shows the ODI, SpO2 and pulse

The ODI (Oxygen Desaturation Index) shows the sum of the relevant oxygen deaturations per hour. Since it is difficult to imagine this definition, I would like to try to explain the whole thing by way of an example:

While we suffer from an apnea or hypopnea, our body is supplied with less oxygen. The logical consequence is that less oxygen also enters our blood. If our oxygen saturation falls by more than 4%, the tolerance limit is exceeded and one speaks of a desaturation. So the ODI now sumupts up exactly those desaturations every hour.

Normal ODI values

Here we should look closely at the values. Basically, an ODI under 10 is good.
However, the ODI should always be assessed in combination with the course of oxygen saturation.
In order to assess the ODI correctly, the SpO2 values should be considered during a desaturation. If these are usually below 90% and the ODI has a score of over 10, this can already be an indication of a sleep disorder. A closer look and a visit to the sleep laboratory are recommended.

ODI values State
Under 10Normal
Over 10They can be normal values. The desaturations should be looked at more closely, however
Over 3030 desaturations per hour is too much. Under no circumstances should these values be permanent.

Why is the ODI important?

If our oxygen saturation falls below 90%, this is considered non-tolerable and subject to treatment. In reality, however, it appears that even healthy people have saturation waste down to less than 90%. The reasons are very varied. It can be due to the evening beers or the midnight snack or even a cold-related snoring.

Let’s say everyone who has had a desaturation is treated directly in a sleep lab. This would end in a huge capacity bottleneck and simply break the scope. That’s why the ODI is such an important index for sleep physicians. It simply indicates the extent of our desaturations. The bigger the ODI, the more desaturations per hour, the more critical my condition is.

An ODI study confirms the relevance of this value for sleep assessment. The study was published here.
You can also download the full study directly here as a PDF:

Oxygen saturation and ODI as a basis for assessment

Of course, many more values are used for evaluation in a sleep laboratory. These include, for example, sleep noise, ECG, EEG and many more…

For home or pre-assessment, SpO2, ODI and pulse are perfectly sufficient. It is important to look at the values over a certain period of time. So you should record your sleep for at least a week and look at the values in their development. Do they improve, do they deteriorate or nothing changes at all? This is important because every night is different. Just because I had a lot of desaturations today doesn’t mean that it’s like that every night. As I said before, there are many factors influencing our sleep.

Conclusion

To be able to monitor and evaluate your own sleep, simple sleep trackers are sufficient. So it is not necessary to buy your own sleep laboratory for thousands of euros and to wire up completely every night. Thanks to the ever-faster developing technology, there are already very small yet highly precise sleep trackers.
But beware! Many so-called sleep trackers claim to be able to monitor your sleep. In fact, often only the pulse is measured. And those devices that also measure SpO2 usually only do this every few minutes. This is far from enough for a qualitative sleep record!


For example, the CIRCUL ring measures continuous 100 times per second. Not only the pulse, but also SpO2 and ODI.
It is therefore perfect for sleep tracking. Because the alternative are finger clips, which are simply uncomfortable to wear and usually fall off at night. The CIRCUL ring has no time function like a smartwatch… Well, in the end, it’s up to everyone.

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Oxygen saturation and ODI in sleep

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