You just had your Home Sleep Study done – but what does all that stuff in the report mean?


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Understanding Your Sleep Report

Trying to understand your sleep study is difficult for most patients, unless you understand the meanings of all the abbreviations referenced in the report. The severity of Obstructive Sleep Apnea (OSA) is important to know because it influences the risks to the patient as a result of untreated OSA including:  1. High blood pressure 2. Heart attack  3. Stroke  4. Diabetes 5. Dementia 6. Alzheimer’s 7. Impaired mental clarity (brain fog).

Without getting too technical, here are some things to help you understand your sleep study. Doctors use the sleep test (PSG or polysomnogram) as a diagnostic tool to make a diagnosis of the patient.  Often, there is simply not enough time to fully explain to the patient how to interpret the results and what it all means. The report is written for doctors and is not patient friendly and can be totally bewildering.  Basically the doctor just tells the patient that they have tested positive for OSA and that they need to seek treatment without going into any great detail.

Now the patient is left holding a complicated medical report that can only be read by a board certified sleep neurologist/physician. Let’s take a little time to try to demystify what is in that 3-4 page report.

The main markers to watch are how many times did the patient stop breathing (AHI) and how much oxygen is the brain receiving(Sp02 saturation) and how many respiratory disturbances were there (RDI) . Of all the numbers on your sleep apnea test report, the AHI is the most important.  AHI as it is the most commonly used term and is an acronym for “Apnea-Hypopnea Index.”  Look for the O2 nadir. That is the lowest percentage of oxygen in your blood going to your brain and organs. It should be above 90%.  If you see the O2 nadir down into the 70%-80% that is usually a serious concern.

Apnea Defined

Apneas are a type of abnormal respiratory event that occur during sleep. The word originates from the Greek roots meaning “without” and “to breathe.” The American Academy of Sleep Medicine (AASM) provides a scoring manual that delineates how all aspects of a sleep study should be interpreted, including defining what constitutes abnormal respiratory events such as apneas. To score an apnea on a sleep study there must be essentially no airflow (measured through a nasal air pressure sensor) for at least ten seconds.  A blood oxygen drop, known as ODI is the oxygen desaturation index (Sp02), it is not part of the criteria for an apnea, but it is a critical metric to how many times your oxygen drops over 3-4%.

Apneas: total cessation of breathing

In an obstructive apnea there is a TOTAL upper airway obstruction resulting in no airflow into the lungs (the nasal pressure and/or thermistor sensors show no signal) but respiratory effort is sustained (the chest belt sensor signal is maintained), meaning that you are trying to breathe but the obstruction will not allow air to pass to the lungs. This is usually caused by a collapse of the soft muscular airway between the throat and trachea and is appears to be unique to the human race.

Hypopneas: restricted airflow causing increase in effort to breathe and decreases airflow to lungs

Hypopneas are the other major type of abnormal sleep breathing event scored on a sleep study. Overall, hypopneas are more common than apneas. The word “hypopnea” is derived from the Greek roots meaning “under” and “to breathe.” So you are breathing but not deep enough for best oxygen transfer in the lungs.


What is ‘AHI’ on a Sleep Apnea Test?

AHI Explained

Let’s use a hypothetical patient to illustrate how the AHI is calculated. Bill just received his sleep study test report back and it says that he slept for a total of 360 minutes (six hours).  During the study, he had 60 apneas and 120 hypopneas. The AHI is calculated as follows:

AHI = (total apneas + total hypopneas) / total sleep time in hours

Therefore, Jim’s AHI is: (60+120)/6 = 30   What it means – Jim stops breathing for 10 seconds or more, 30 times every hour. That means once every 2 minutes!  Each time he stops breathing there is  a micro arousal that keeps him from entering his deeper sleep pattern giving him a fractured sleep architecture which hinders all  of the reparative and rebuilding mechanisms in your body and brain to repair and heal during the night.

What are Arousals?

An arousal occurs when your SpO2 level drops and C02 levels rise due to breathing cessation. This triggers your brain to awaken just enough to open the airway, but not enough to awaken the person from their sleep.

OK, so how exactly does that happen when I am asleep? 

Your body and brain are amazing in how they work together to keep us alive and healthy.  There are oxygen (02) and carbon dioxide receptors (C02) that are located in the carotid arteries in your neck.   When your breathing stops oxygen is not being brought into the lungs and carbon dioxide is not being expelled.  In just a few seconds these sensors pick up on the dropping oxygen levels and rising carbon dioxide levels and sends warning signals to the brain.

The brain immediately goes into action to get more oxygen to the brain and organs, so it increases the heart rate which increases the blood pressure. The sensors send signals continuously to the brain and when there is still no increase in the oxygen levels then the brain tells your jaw muscles to clench down with your teeth to help open the airway – the brain creates muscle movements to reposition the body to open the blocked airway to regain breathing function to get air to the lungs.

All of this happens without the person actually waking up – so it is often referred to as a micro-arousal.

End Result 

So, you can see, that if this is happening every 2 minutes as in Jim’s case, his brain really never gets a chance to rest, nor does his heart and a myriad of the restorative events that occur in the deep sleep levels. The net result is fractured sleep patterns, oxygen deprivation to the brain and organ tissues and the person develops all symptoms of OSA disease that result in decrease in energy, chronic illnesses, decreased quality of life, brain fog, dementia, and an overall  shorter life span.

Rating the severity of OSA

Sleep apnea is divided into three categories by AHI:

Mild sleep apnea: AHI ≥ 5 –  15   Moderate sleep apnea: AHI  15 – 30  Severe sleep apnea: AHI over 30+

Using the above criteria with an AHI of 30 Jim is on the border between Moderate and  Severe Sleep Apnea based on this AHI calculation.

We hope this demystifies the data in your sleep report. If you have any questions just drop us an email at info@sleephouston.com.

Sleep Well

Dr. Hans Schleicher

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