The Sleep Apnea Test

About 25 million adults in the United States suffer from sleep apnea, a public health and safety issue that contributes to high blood pressure, heart disease, type 2 diabetes, stroke, and depression, according to the American Academy of Sleep Medicine (AASM).

If you think you may have sleep apnea, you should talk with your doctor or, if your insurance company allows coverage without a referral, go directly to a sleep specialist. These doctors come from a variety of medical backgrounds including pulmonology, otolaryngology, neurology, and psychiatry.

They record your medical history and health conditions, and conduct an evaluation to determine if you are a candidate for home sleep apnea testing, or if you qualify for an overnight sleep study at a sleep center. Your doctor will diagnose you with sleep apnea based on the outcome of your sleep study.

Let’s take a closer look at common tests for sleep apnea.

Types of Sleep Apnea Tests

Your sleep physician may ask you to take a sleep test, called a polysomnogram. Whether you have a home sleep apnea test or undergo a polysomnography at a sleep lab, your brain activity, breathing patterns, and blood-oxygen levels will be closely monitored. 

Your doctor will review the data from your sleep test to determine your apnea-hypopnea index, or AHI. This determines the severity of your sleep apnea and what treatment you qualify for, if any. AHI is the sum of the number of apneas (times you stop breathing) and the number of hypopneas (or the periods of shallow breathing) that occur each hour. Normal sleepers have an AHI score of fewer than five events per hour while someone with severe sleep apnea will have an AHI measurement of 30 or more events per hour. 

1. Simple Oximeter Home Sleep Test 

This is the simplest of all sleep studies, and it only uses 2 parameters to determine if you have sleep apnea:

• Finger Pulse Oximeter – To monitor the level of oxygen in your blood
• Heart Rate Monitor –To look out for elevated heart rate

This type of test kit can be found at a pharmacy or chemist, but if you choose the latter, be sure you call and make an appointment first.

Who is best suited for this kind of study?

People who experience signs and symptoms of sleep apnea, such as constant daytime sleepiness and snoring, or think they have sleep apnea could benefit from this study. This test is also better for overweight candidates with a Body Mass Index (BMI) of more than 25.

The overnight oximeter kit usually consists of a small machine that straps onto your wrist to measure your heart rate, and a clip that attaches to one of your fingers to check the oxygen levels in your blood. You are expected to wear the devices at night while you sleep. The oximeter looks for a drop in your blood oxygen levels and a rise in heart rate — indicators of obstructive sleep apnea. While this test can identify symptoms generally associated with sleep apnea, it may not accurately detect the sleep disorder in people who have mild sleep apnea symptoms.

Preparations for this study

The oximeter sleep study is simplistic enough that little prep work is needed other than a pre-sleep questionnaire to complete prior to your test. You’ll also want to be sure to sleep long enough so there is plenty of data available to provide the most accurate test results.

For best results, remove all nail polish, and don’t overindulge in alcohol before taking this test. Stick to your normal sleep/wake schedule as close as possible. When you wake in the morning, remove the device and return it to the pharmacist for analysis. The turnaround time for this test is generally 8-10 days.

2. Home-Based Sleep Study / Ambulatory Home Sleep Study

This sleep study is more involved than the oximeter, but it is also slightly more accurate. Most involve a machine that’s attached to the center of your chest with wires and electrodes coming out of it. Some of the parameters it monitors for include:

• Electroencephalography (EEG)/ Electrooculography (EOG) – Measures brain waves and eye movements
  • These electrodes are usually situated on the lateral corner of your eyes, the center of your forehead, and on the bony structure behind your ear. They are used to see what stage of sleep you are in.
• Respiratory Belts – Measures breathing movements
• Nasal Cannula – Detects for nasal breathing
• Oral Thermistor – Detects for mouth breathing
• Finger Pulse Oximeter – Monitors the level of oxygen in your blood
• Body Positioning Sensor – Records if you are a side or back sleeper

Who is best suited for this kind of study?

This study is usually recommended for people who are able to follow simple instructions at home. This is also suitable for all patients who suspect they may have sleep apnea.

Preparations for this study

Prior to setting up the sleep study kit, you will also need to complete the pre-sleep questionnaire. This test requires you to attach all the gadgets onto yourself before going to bed, so you will need to begin setting up the sleep kit about 30 minutes before bedtime.

An instruction card with words and pictures is included to guide you through the steps. Remember to remove all nail polish and stick to your normal sleep and wake up time. 

The next morning, remove all the devices and return the sleep study kit for analysis. It takes longer to generate these additional reports for this study. You can expect your test results in about 2 weeks.

3. In-Lab Polysomnographic Sleep Study 

This is the most extensive sleep test to accurately detect obstructive sleep apnea and its severity. This study requires you to be admitted to a hospital sleep lab overnight. A sleep technologist works to ensure all signals and electrodes are placed properly on your body. An infrared night vision camera is used to monitor your sleeping patterns. 

Parameters recorded during this study include:

• Finger Pulse Oximeter – Monitors the level of oxygen in your blood
• Nasal Cannula – Detects for nasal breathing
• Electroencephalography (EEG)/ Electrooculography (EOG) – Measures brain waves and eye movements (In this study, there will be 2 pairs of each electrode)
• Oral Thermistor – Detects mouth breathing
• Respiratory Belts – Measures breathing movements and looks for breathing disorders, uses electrodes on the upper chest and on the level of your navel
• Electrocardiogram (ECG) – Monitors heart rate and checks for irregular heart rhythm
• Body Positioning Sensor – Records your sleep position — side, back, or stomach 
• Electromyography (EMG) – Electrodes placed at your jaw muscles to detect teeth clenching and grinding
• LegEMG – Similar to the electrodes placed at your jaw muscles, except these are placed on your leg muscles to detect restless leg movements or muscle twitches
• Snoring Sensor – A small microphone placed on the neck to detect for vibrations and snoring
• Infrared Night Vision Camera – Camera used by the sleep technician to oversee the study

Who is best suited for this kind of study?

This study is suited for anyone with suspected sleep apnea. It is extremely accurate and especially good for people who require additional assistance in the middle of the night such as with bathroom breaks. It is also good for the elderly who are unable to conduct home sleep studies themselves.

Preparation for this study

Prior to arriving at the hospital, have dinner and make sure all nail polish is removed. Remember to bring pajamas, toothbrush, shampoo, soap, and all the amenities you need for the next morning. Most sleep labs will provide you with your own private room and bathroom. Towels are usually provided as well.

After arriving at the sleep center, usually around 8 or 9 p.m., a sleep technician will have you complete a pre-sleep questionnaire before setting you up on all the monitoring devices. This process will take up to an hour. In the morning, it takes about 20 minutes for the technician to unhook you from the devices. You’ll be asked to complete a post-sleep questionnaire before being discharged. It will take about two weeks to get your test results.

4. In-Lab Titration Polysomnographic Sleep Study 

This study is very similar to the previous in-lab study discussed, but the In-Lab Titration Polysomnographic Sleep Study is generally offered to people who have already been diagnosed with obstructive sleep apnea, and are candidates for CPAP (Continuous Positive Airway Pressure) therapy. The purpose of this test is to identify the proper positive air pressure settings for that patient.

All the parameters recorded will be exactly the same as the In-Lab PSG Study. The only difference is instead of the nasal cannula and oral thermistor, you will wear a CPAP mask. The sleep therapist will help you try on a few masks to ensure you are fitted with the most comfortable one for you.

During the night, the sleep therapist will remotely adjust the amount of CPAP pressure needed to eliminate all apnea events. By the end of the study, the sleep technician will prescribe the most suitable pressure level to alleviate your apnea events.

Types of Sleep Apnea 

There are four types of sleep apnea:

Hypopneas — The most common type, hypopneas are episodes of shallow or slow breathing caused by a partial block in your airway. This causes a drop in blood oxygen saturation. 

Obstructive sleep apnea — Obstructive sleep apnea is more severe than hypopneas. It occurs when your airway is completely blocked and you stop breathing for 10 seconds or more. Risk factors for obstructive sleep apnea include being overweight or obese. 

Central sleep apnea — Central sleep apnea is not as common as obstructive sleep apnea, but is unnerving nonetheless. Rather than your breathing stopping due to an actual blockage of the windpipe, central sleep apnea is caused by a communication breakdown between your nervous system and the muscles that control your breathing. 

Mixed sleep apnea — Mixed sleep apnea is a combination of obstructive sleep apnea and central sleep apnea. It generally starts with episodes of central sleep apnea followed by a bout of obstructive sleep apnea. 

Understanding Test Results 

Results from your sleep study will give your sleep specialist information to diagnose you with sleep apnea, identify the severity, and determine the best treatments for your condition. Here are some test results they may consider:

Apnea Hypopnea Index (AHI) — Your AHII determines the severity of your sleep apnea. The number is the sum of the number of apneas, or times you stop breathing, and the number of hypopneas, or the periods of shallow breathing, that occur each hour. Normal sleepers have an AHI score of fewer than five events per hour while someone with severe sleep apnea will have an AHI measurement of 30 or more events per hour.

Respiratory Disturbance Index (RDI) — Also called respiratory distress index, RDI is similar to AHI in that it reports on respiratory events while you sleep, but it also includes respiratory-effort-related arousals, or RERAs.

Respiratory-Effort-Related Arousals (RERA) — This occurs when breathing stops for 10 seconds or longer, causing a sudden change in your sleep cycle. This is identified as a sudden shift in your brainwave activity during sleep. 

SpO2 Nadir — SpO2 refers to “arterial oxygen saturation,” and Nadir means “the lowest point.” So, SpO2 Nadir translates to “the lowest amount of oxygen in your arterial blood.” This is recorded by a clip on your finger and is read in percentages. A healthy person typically has a blood oxygen level around 95-96% when awake, which drops down to about 92-90% while sleeping. If it drops below 90%, there is cause for concern, especially if it is associated with an apnea event. Oxygen levels that fall more than 4% at one time will activate your body’s “fight or flight” response, jolting you awake and causing your heart rate to increase to compensate for the loss of oxygen. 

Arousals — Also known as “wake events,” arousals occur when the body enters the “fight or flight” response triggered by apnea-induced low oxygen event. People may or may not be aware when this is occurring. Some may wake in the middle of the night feeling panicky during or immediately after an arousal episode

Heart Rate — Your resting heart rate depends on your age and level of fitness. On average, it is about 70 beats per minute. If you are a marathon runner, you may have a resting heart rate as low as 50 beats per minute. Many sleep tests monitor your heart rate to detect spikes or fluctuations, which may signal a drop in oxygen due to an apnea. 

Sleeping position — By monitoring which position you are in while sleeping — back, stomach, or side — your sleep test may detect in which position you have fewer apneas. Typically, back sleeping puts you at greater risk for apneas because the relaxed soft tissues in the mouth are more susceptible to gravity and thus to falling into the back of your throat. 

Snoring Index —  This test measures the intensity of your snoring during the night. If you snore, it  does not necessarily mean you have sleep apnea. 

Periodic Limb Movement Syndrome (PLMS) — Sleep tests also monitor for PLMS, a condition in which your arms or legs move involuntarily during sleep. These uncontrollable movements can happen every 10 to 60 seconds while you sleep, and interfere with a good night’s rest. People who suffer from restless leg syndrome (RLS) are more likely to suffer from PLMS than people without RLS. 

Next Steps for People Newly Diagnosed with Sleep Apnea 

Your sleep specialist will consider all the data from your sleep apnea test to diagnose you. Your Apnea Hypopnea Index, or AHI, which counts the number of apneas (times you stop breathing) and hypopneas (periods of shallow breathing) that occur each hour, is the score that will determine the severity of your sleep disorder and what treatments, if any, are recommended. 

Levels of S

None/Normal — An occasional bout of apnea is not considered an issue. Having an AHI of less than 5 per hour is considered normal and generally requires no treatment. 

Mild Sleep Apnea — People who have between 5-15 apneas per hour are diagnosed with mild sleep apnea. Treatment usually involves lifestyle changes like weight loss, sleep positioners to keep you from rolling from your side to your back, or sleep apnea devices like oral appliances. 

Moderate Sleep Apnea — People with moderate sleep apnea have an AHI score of 15 to 30 per hour. Lifestyle changes and sleep apnea devices are the first-line of treatment recommended at this stage. If those treatments don’t work, your sleep doctor may recommend CPAP therapy. 

Severe Sleep Apnea — People who experience 30 or more apneas per hour are considered to have severe sleep apnea. CPAP therapy is usually recommended. For patients who cannot tolerate positive airway pressure therapy, medical procedures and surgeries may be an option.