The aim to diagnose sleep apnea is not just to record the presence of this sleep disorder but to identify its type: whether it is obstructive or central or mixed (both obstructive and central). The causes of both these types are different and so is their treatment options.
The diagnosis of this condition is based on the evaluation of the medical history and the symptoms presented by the patient and/or his or her bed partner, physical examination, and the results of a sleep study called polysomnography.
You will be referred to a sleep disorder center where the sleep specialist will begin his diagnostic procedure and advise the treatment accordingly.

Diagnosis guidelines for sleep apnea

Sleep apnea is a greatly under-diagnosed condition. It is estimated that about 90% of the people who have this condition do not know that they have it.

The reasons for this are that the symptoms are vague, develop gradually, and they appear when you are asleep. You, therefore, do not realize their presence.
Secondly, the knowledge of sleep apnea is still poor among the population and physicians. Thirdly, its diagnostic test is expensive.

Your doctor proceeds through the following sequence to diagnose your sleep condition. 

Medical History and Symptoms

The sleep specialist will ask you and your bed partner for your presenting symptoms, which the patient will elaborate (such as loud snoring, which awakens those around).
The specialist will take a detailed medical history of any illnesses, the patient may have had or has and which could match with any of the sleep apnea causes
If you stop breathing for 10 or more seconds during one episode when you are sleeping, you may have sleep apnea.
The presence of an average of five such episodes per hour every night can be officially diagnosed as sleep apnea.

Physical Examination

Physical examination of the nose and mouth helps to rule out an enlarged tonsil or uvula or a soft palate or a deviated nasal septum, which could be the cause. Other causes too, can be ruled out by a thorough physical examination.

Polysomnography

After your symptoms and signs have suggested that you may be having sleep apnea, your sleep doctor will suggest polysomnography (PSG) to confirm the diagnosis. This is the most accurate method to diagnose sleep apnea.
It measures a number of your physical and physiological activities while you are asleep. It also monitors your sleep stages and patterns to see if your sleep cycle is disrupted during sleep.
Polysomnography, also called nocturnal polysomnography, is the most common sleep study, which is usually done at a sleep center at night when you are asleep.
Among other things, it records your
• brain waves with an EEG machine
• the oxygen level in your blood with a pulse oximeter
• heart rate with an ECG machine
• breathing with a nasal airflow sensor
• eye movements with an electrooculogram
• and leg movements with an electromyogram
Sleep apnea can be mild, moderate, or severe, depending on the frequency of your apneas (cessations of breathing) in an hour.
The episodes of apneas may occur from 5 to 100 times an hour. More than five apneas per hour is abnormal. If the study records more than 30-40 apneas per hour, the condition is considered to be severe.

CPAP to diagnose obstructive sleep apnea

CPAP or continuous positive airway pressure is used in cases where obstructive sleep apnea has been diagnosed. If you have OSA, you will be required to undergo a test again wearing a mask that provides positive pressure.
The CPAP mask prevents the collapse of your airway during sleep and helps maintain proper breathing. At times, a split night study is carried out in which the CPAP mask is used during the second half of the night after the evaluation during the first half is carried out without CPAP.

Home Sleep Monitor

In certain circumstances, a home monitor is used, which records the activities mentioned above when you are asleep. A technician comes to your home, applies the monitor at night, and takes away the recordings in the morning.
Once sleep apnea is diagnosed with the associated problem (such as a lung or heart problem), you may be referred to the concerned specialist to treat the problem that is causing either the obstructive or central type of sleep apnea.
The advantage of the home monitoring method is its lower cost and you do not have to spend the night in a sleep center.
The disadvantages of home sleep monitoring are its inability to resolve any technical issues that may arise, inability to diagnose other sleep disorders, inability to diagnose total sleep time, the requirement of an attendant to fix and remove the equipment and, an improper application may give false results.
Another disadvantage is that a home test measures breathing only and not the actual sleep, so the outcome can be inconclusive or the reading can be falsely negative.

Other Studies for Central Sleep Apnea

If you have central sleep apnea, you will be required to undergo some further tests to diagnose the underlying cause.
CSA is caused by the brain not sending the proper signals to the respiratory muscles to carry out the process of breathing. Here, therefore, the brain and the muscles have to be investigated to rule out any pathology.
Such tests will include:
• Blood tests
• CT scan of the brain or a brain MRI
• EEG studies (of the brain to measure its electric activity)
• EMG studies for nerve conduction of electrical impulses

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