Polysomnography
Polysomnography is conducted to perform a sleep study. This test, which can be either daytime or nighttime, helps detect disorders that affect various bodily functions during sleep.
General Description
Polysomnography is used to detect sleep disorders. This study records heart and respiratory rates, brain waves, oxygen levels, and movements of both the eyes and legs. Typically, this sleep study is conducted at night, but it can also be performed during the day for patients who usually sleep during the day.
Depending on where the sleep study is conducted, there are two types:
- Polysomnography in a medical center: This is the most common option. The patient stays overnight at a hospital or sleep clinic, where they are continuously monitored and supervised. The main advantage is that physicians can control the sleep conditions.
- Home polysomnography: This is mainly used for respiratory polysomnography, which means that only respiratory-related data is monitored during sleep (such as snoring, blood oxygen saturation, respiratory effort, or nasal airflow). It is commonly used to diagnose sleep apnea and helps avoid altering the patient’s sleep habits, ensuring that the results are not affected by external factors.
The analysis of polysomnography results helps diagnose conditions such as sleepwalking, narcolepsy, hypersomnia, sleep apnea, snoring, or restless legs syndrome. It is also used to determine the most appropriate treatment for each case or to assess the effects of an ongoing treatment.
When is it indicated?
Polysomnography is used to check if sleep patterns are disrupted and, if so, to determine the cause. It is indicated when a patient presents symptoms such as:
- Excessive daytime sleepiness.
- Excessive leg movement during sleep.
- Getting up, talking, or making rhythmic movements while asleep.
- Sudden sleep episodes during the day.
- Temporary breathing cessation during sleep.
How is it performed?
Various parameters can be measured in a sleep study, leading to four different types of tests:
- Baseline polysomnography: This is the standard test. The patient sleeps with electrodes placed on the scalp to measure brain activity and eye movements, on the chest to record heart activity, and on the chin and legs to register both movement and muscle activity. Additionally, bands are placed around the chest and abdomen to measure respiratory effort, a pulse oximeter is attached to the index finger to indicate oxygen saturation, and a sensor is placed on the nose and mouth to record airflow. Finally, video and audio recordings are made while the patient sleeps.
- Polysomnography with CPAP titration: This includes a continuous positive airway pressure (CPAP) mask to gradually apply pressurized air, reducing breathing pauses during sleep.
- Polysomnography with BiPAP titration: In addition to the baseline test, a bilevel positive airway pressure (BiPAP) device is used to generate different air pressures during inhalation and exhalation. This is useful for patients who require higher pressure than a CPAP can provide.
- Split-night polysomnography: The test begins with a baseline study during the first two hours of sleep, and if respiratory pauses are detected, it transitions to a CPAP titration test.
Risks
Polysomnography does not pose any health risks for the patient.
In rare cases, allergic reactions to the electrodes or the adhesive used to attach them may occur.
What to expect from a polysomnography
Before undergoing polysomnography, the patient must sign an informed consent form. Then, they should follow their usual bedtime routine.
Once all the sensors are in place, the patient must remain in bed without reading, watching TV, listening to the radio, or using electronic devices. In other words, once the test begins recording vital information, the patient should only lie down and try to sleep. In the morning, after the test concludes, they can resume their daily routine immediately.
In some cases, the doctor may request additional tests, such as a multiple sleep latency test, which records data during several naps taken throughout the day after the polysomnography, or a maintenance of wakefulness test, which analyzes the patient’s ability to stay awake in passive situations.
Results are usually available several days after the test.
Specialties that request polysomnography
Polysomnography is a test commonly performed in sleep units or the clinical neurophysiology specialty. It is typically requested by the Pulmonology and/or Neurology specialties.
How to prepare
To undergo a sleep study, the patient should arrive at the medical center after dinner and having taken their usual medication. It is recommended to shower, shave, and wash their hair without using styling products that might prevent the electrodes from adhering properly to the scalp.
In cases of home polysomnography, the patient must place the sensors and pulse oximeter themselves, following medical instructions, and remove them in the morning. Afterward, they must return the recording device to the medical center for analysis.
On the day of the test, patients should avoid naps, caffeine, and alcohol. Additionally, maintaining a regular sleep schedule—sleeping seven to eight hours each night—for the preceding week is recommended.
Patients undergoing CPAP treatment at night must discontinue its use 15 days before the polysomnography.
