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Sleep Disorders

Effects of Low Blood Oxygen Levels

10/20/2008

Question:

I was diagnosed with central and obstructive sleep apnea about one year ago. My first CPAP machine did not resolve my symptoms and I was switched to a Respironics Auto SV BiPAP machine w/ two liters of oxygen about four months ago. I had an overnight pulse oxygen test last week. The results show that I had two periods between 30 and 45 minutes where my blood oxygen level fell into the low 80s and even the upper 70s. Is an hour to hour and a half of low blood oxygen a problem? What are the possible effects? And, could it explain why I am still tired.

Thanks very much.

Answer:

You seem to have a good grasp on the nature and details of your sleep disorder. I’m afraid that sleep-related hypoxia to the extent that you mention is not normal. However, with home testing devices there is a possibility that the results of the test that you had (nocturnal oximetry) are wrong. Technical issues, namely poor signal quality, may result in falsely low oximetry recording.

Other causes of sleep related hypoxia may be any, or a combination of, the following:

1. Sleep-related hypoventilation: this is when breathing becomes shallow during sleep. This is most common during Rapid Eye Movement (REM) sleep, also known as dream sleep. During REM sleep we breathe less deeply and are therefore at risk for becoming hypoxic.

2. Persistent sleep apnea: this includes residual central and obstructive sleep apnea. Sleep apnea can be worse during certain sleep stages, or during certain body positions. Treatment of sleep apnea with positive air pressure devices (CPAP/BiPAP/ASV/Oxygen) in the lab may not be adequate if sleep at home is significantly different from sleep in the lab.

3. Ventilation/Perfusion mismatch (due to underlying lung disease): this can cause a disturbance in the flow of blood and oxygen in the lung. This imbalance will result in low oxygen levels.

If the hypoxia found on your test is accurate, and is left untreated, it may carry ill effects on your health. These complications may include any of the following:

1. Heart rhythm disturbances (mostly in people who are at risk or already have heart problems).

2. Heart muscle dysfunction. This was noted in experiments done of hypoxia in rats.

3. Increased pressure on the right side of the heart. This was noted in people who have as little as 5 minutes of continuous hypoxia during sleep.

4. Sleep quality may suffer. This is due to sleep fragmentation which can result from hypoxia itself or may show up as an indirect sign of under treated residual sleep apnea.

Since the causes of hypoxia during sleep are variable, and because this may result in serious effects on a patient’s health, it is important to pursue further diagnosis and treatment of underlying cause. The specific therapy will depend on the reason for the low oxygen levels. In some cases, a simple increase in oxygen supply may be all that is needed.

I advise you to discuss these issues with your physician as soon as possible, particularly since you seem to have persistent symptoms that can be directly related to sleep hypoxia.

Additional information regarding sleep can be obtained on the American Academy of Sleep Medicine website. This website contains a list of Sleep Centers across the country so you can find one if you need it.

I wish you the best of health.

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Response by:

Ziad  Shaman, MD Ziad Shaman, MD
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University