Investigations for Obstructive Sleep Apnea

Polysomnography

Basically a diagnostic sleep study. Measures sleep cycles of a person by recording information such as:
-Blood oxygen levels (Oximeter)
–Body position (Device placed on chest)
–Brain waves (EEG): Measurement of electrical signals from the brain to determine whether you are awake or asleep and what stage of sleep you are in.
–Breathing rate
–Eye movement (EOG) – to determine REM sleep. Some people have worse symptoms in REM sleep.
–Heart rate

AHI measures the number of atypical breathing incidents during 1 hour of sleep. An AHI of 5 or less is normal; 5 to 14 is mild obstructive sleep apnea; 15 to 29 is moderate obstructive sleep apnea; more than 30 is severe. RDI is AHI/hr. All oxygen desaturations <90% during sleep are considered medically significant.

Performed at a special sleep center. The test is often done during the night so that your normal sleep patterns can be studied. Electrodes will be placed on your chin, scalp, and the outer edge of your eyelids. These must remain in place while you sleep.

Signals from electrodes are recorded while you are awake (with your eyes closed) and during sleep. The time it takes you to fall asleep is measured, as well as the time it takes you to enter REM sleep.

Monitors to record your heart rate and breathing will be attached to your chest. These also must remain in place while you sleep. A specially trained health care provider will directly observe you while you sleep and note any changes in your breathing or heart rate. The number of times that you either stop breathing or almost stop breathing will be measured. In some sleep study centers, a video camera records your movements during sleep.


Multiple Sleep Latency Test: In some cases, a multiple sleep latency test is performed on the day after the overnight test to measure the speed of falling asleep. In this test, patients are given several opportunities to fall asleep during the course of a day when they normally would be awake.

At-Home Sleep Apnea Test: To diagnose sleep apnea, a portable test, which can be conducted at home can be used as an alternative to polysomnogram for diagnosing obstructive sleep apnea. The home tests are portable devices that are composed of a recording device, belts, sensors and other cables. The data gathered overnight has to be reviewed by sleep specialist and thereby diagnosis and treatment plan has to be developed.


Sleep studies can also determine whether you have a problem with your stages of sleep. Normally, NREM and REM alternate 4 to 5 times during a night's sleep. A change in this cycle may make it hard for you to sleep soundly. Non-REM sleep is in turn further divided into four different stages (1 through 4), with stages 3 and 4 often referred to as "deep sleep." Normal sleep patterns break down your time asleep as follows: stage one sleep for 5% of the time, stage two for 55% of the time, stage three and four at 20% of the time and REM sleep for 20%.

ECG

Not a gold standard exam to diagnose OSA. Research has been done to diagnose OSA using ECG, with high success rate (80 to 95% accuracy). Use of algorithms. However, in a sleep study, ECG is used to detect irregularities in heart beat or rhythm. Complications of OSA is right ventricular hypertrophy, which may eventually lead to cor pulmonale. Also may be left ventricular hypertrophy. Can be detected by ECG – right or left axis deviation.