Evie Summers
Sleep is a time when the body is at rest, but that doesn't mean nothing is happening. During sleep, your body temperature drops, your heart rate and blood pressure go down, and your breathing slows. In fact, your oxygen levels are lower when you sleep, and carbon dioxide levels are higher. This is true for both REM and non-REM sleep, though during REM sleep, your breathing rate increases and becomes more shallow and irregular. This may be due to throat muscles relaxing or reduced movement of the rib cage.
| Characteristics | Values |
|---|---|
| Oxygen levels in the blood | Lower during sleep |
| Alveoli | Some drop out of use during sleep |
| Breathing rate | Slower during non-REM sleep |
| Breathing rate | Faster during REM sleep |
| Breathing | More shallow and less regular during REM sleep |
| Coughing | Less common during sleep, especially REM sleep |
| Oxygen consumption | Gradually decreases in the first 4 hours of sleep |
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What You'll Learn
Oxygen levels are lower during sleep
It is a fact that everyone's oxygen levels in the blood are lower during sleep. This is due to a mildly reduced level of breathing. During the day, breathing changes depending on what you are doing and feeling. In contrast, during non-REM sleep, which accounts for about 80% of an adult's sleeping time, breathing is slow and regular. However, during REM sleep, the breathing rate increases, and it becomes more shallow and less regular. This may be caused by throat muscles relaxing and reduced movement of the rib cage.
During sleep, oxygen levels are lower, and carbon dioxide levels are higher due to the slight decrease in breathing. This is supported by a study that measured oxygen consumption in eight normal male volunteers during sleep, which found that the minimum oxygen consumption was 7.9% lower than the first hour.
While sleeping, the body prioritises other functions, such as cell repair and digestion, over breathing. This decrease in breathing rate is normal and helps the body conserve energy. However, some people may experience breathing disorders such as sleep apnea, which can cause oxygen levels to drop to dangerous levels.
If you are concerned about your oxygen levels during sleep, it is important to consult a healthcare professional. They may recommend an overnight oximetry test to measure your oxygen saturation levels while you sleep.
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Obstructive sleep apnea
The primary symptoms of OSA include loud, disruptive snoring, witnessed apneas during sleep, and excessive daytime sleepiness. However, many people with OSA are asymptomatic and may not experience any noticeable symptoms. For those who do exhibit symptoms, OSA can significantly impact their quality of life, cardiovascular health, mental health, and driving safety.
The risk factors for OSA include obesity, hypertension, and craniofacial abnormalities. The condition is more prevalent in middle-aged and older adults, with men being more commonly affected than women.
The diagnosis of OSA typically involves a sleep study, which can be conducted in a specialised facility or at home. Treatment options include continuous positive airway pressure (CPAP) therapy, oral appliances, weight loss strategies, and surgical interventions.
OSA is a serious condition that requires medical attention. If left untreated, it can lead to major health complications, including heart failure, high blood pressure, and an increased risk of accidents due to excessive daytime sleepiness.
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Overnight oximetry test
An overnight oximetry test is a simple, safe, and painless diagnostic procedure used to determine a patient's blood oxygen level and heart rate over the course of a night's rest. It is often used as part of the initial evaluation process for respiratory disease, helping to identify the need to start, continue, or increase home oxygen therapy. The test can also be used to screen patients for Obstructive Sleep Apnea (OSA) prior to a home sleep test or in-lab sleep test.
During the test, an oxygen sensor is placed on the patient's finger. This sensor sends data to an oximeter, which measures and records the patient's heart rate and blood oxygen levels. The oximeter can be used during sleep or for spot checks while the patient is awake. Newer oximeters may adhere directly to the skin and provide similar measurements.
The overnight oximetry test is typically performed in the patient's home, making it a convenient and cost-effective way to measure blood oxygen levels. The data collected by the oximeter is then shared with the patient's physician, who uses it to determine if oxygen therapy will be beneficial.
The test is easy to use and does not restrict mobility, allowing the patient to move freely while the oximeter is connected. It can also be used as an ongoing tool to ensure optimal therapy is achieved. Additionally, the overnight oximetry test is widely available, with devices purchasable online or at pharmacies.
While the overnight oximetry test is a useful screening tool, it has some limitations. It only provides a limited amount of information, and there are subtleties involved in sleep disorders that may not be detectable through this test alone. For example, sleep position and sleep stages can impact oxygen levels, but simple oximeter devices cannot identify these contributions. Therefore, additional tests, such as polysomnography or more extensive home sleep apnea testing, may be necessary to confirm a diagnosis.
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Sleep-related hypoxemia
Hypoxemia is caused by inflammation or scarring in the lung tissue, making it difficult for oxygen to move into the bloodstream. This can be measured through oximetry or an arterial blood gas study. Treatment for hypoxemia may include supplemental oxygen therapy, which can improve quality of life, exercise tolerance, and survival.
The effects of repetitive intermittent hypoxia, as occurs in sleep-disordered breathing, are generally considered harmful to the cardiovascular system. However, some studies suggest that mild intermittent hypoxia during wakefulness may reduce blood pressure in hypertensive patients. More research is needed to determine the optimal dose and cumulative exposure to intermittent hypoxia, as well as the specific patient subgroups that may benefit or be harmed by this treatment.
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Oxygen consumption during sleep
Factors Affecting Oxygen Consumption During Sleep
During non-REM sleep, which accounts for about 80% of an adult's sleeping time, breathing is slow and regular. In contrast, during REM sleep, the breathing rate increases, and breathing becomes more shallow and irregular. This irregular breathing during REM sleep may be due to throat muscle relaxation or reduced rib cage movement.
Oxygen Consumption and Sleep Stages
Research has shown that oxygen consumption during sleep is influenced by the sleep stage and the time of night. In a study conducted by T Ryan et al., oxygen consumption was measured in eight male volunteers during sleep using the ventilated-hood method. The data collected over 28 nights showed an overall trend of decreasing oxygen consumption in the first four hours of sleep, followed by a rise towards the morning. The minimum oxygen consumption was 7.9% lower than the first hour.
When comparing different sleep stages, the study found that oxygen consumption during the awake stage and stage 1 sleep was significantly higher than all other stages. Stage rapid eye movement (REM) sleep had significantly lower oxygen consumption than stage 2 sleep, but there was no significant difference between stages 3 and 4 or stages REM, 2, and 3.
Health Implications of Reduced Oxygen Consumption During Sleep
While reduced oxygen consumption during sleep is typical, prolonged or repeated gaps in breathing can lead to oxygen levels dropping too low, adversely affecting tissues and organs. This condition is known as sleep-related hypoxemia and can increase the risk of stroke, brain aneurysm, and cognitive impairment. Therefore, it is essential to monitor oxygen levels during sleep and seek medical intervention if levels drop below 92%.
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Frequently asked questions
Yes, your oxygen levels are lower when you're sleeping. This is due to a mildly reduced level of breathing and the fact that some alveoli (air sacs in the lungs) drop out of use.
Low blood oxygen levels can lead to hypoxemia, where your tissues don't receive enough oxygen to function properly. This can cause fatigue, dizziness, and shortness of breath.
A blood oxygen saturation level of 90% or above is considered normal. Levels below 92% are considered low and may require medical intervention.
Your doctor will determine if you need supplemental oxygen by testing your blood oxygen levels while you're at rest and while walking. They may also order an overnight oximetry study to test your oxygen saturation while you sleep.
Supplemental oxygen ensures your organs receive the oxygen they need to stay healthy. It can improve your quality of life, increase your exercise tolerance, and even improve your survival rate if you're hypoxemic.
