Sleep apnea (apnea from Greek for “without breath”), a chronic sleep disorder involving cessation of breathing during sleeps, can be difficult to diagnose. The sufferer is rarely aware of the breathless episodes, and the daytime symptoms are drowsiness, morning headache, dry mouth and raw throat. The most recognizable symptom, usually noticed by family or friends, is loud and excessive snoring. To diagnose sleep apnea, though, requires sleep apnea testing.
Sleep apnea testing is most often performed by polysomnography (PSG), which monitors heart rate, state of sleep, levels of oxygen in the blood, any difficulty in breathing, eye movement and muscle activity. PSG can be performed at home with the help of a special monitor, and a sleep technologist to hook up the machine, but the optimal method is for PSG in a sleep lab.
Sleep apnea testing in a lab consists of monitoring the patient during sleep, and is usually done overnight. The patient performs normal bedtime habits, teeth brushing, gets into pajamas, etc., and is then hooked up to the machines that will measure activities during the night. The set up requires several minutes and includes the following:
A. Surface electrodes: Placed on the skin and scalp to record the electrical energy present during muscle or brain activity.
B. Electroencephalogram, EEG: A major part of the sleep apnea testing, measuring and recording four types of brain activity: alpha, beta, delta and theta waves. Each type of brain wave is associated with a different stage of sleep.
C. Electromyogram, EMG: Records muscle activity including facial tics, grinding of teeth, and leg movements. EMG also helps recognize REM (rapid eye movement) sleep, important in diagnosing sleep apnea.
D. Electro-oculogram, EOG: Records eye movements important in recognizing stages of sleep, especially REM. cpap masks
E. Electrocardiogram, EKG: Tracks and records heart rate and rhythm.
F. Nasal Airflow Sensor: Records breath temperature, airflow, apnea and hypopnea (abnormally slow or shallow breathing).
G. Oximeter: Monitors oxygen levels in the blood.
H. Video: To visually track the movements and positions of the body.
I. Snore Microphone: Records snoring, a major symptom of sleep apnea.
Once the monitors are all hooked up, the patient goes to sleep, on his/her own timetable. How long it takes a patient to fall asleep is also an important part of the sleep apnea testing.
Sleep is a complex activity, so sleep apnea testing must monitor everything related to sleeping, especially the transitions and changes that occur. During sleep the body cycles between NREM (non-rapid eye movement) and REM sleep every 90 minutes or so. Heart rate, eye movement, muscle and brain activity, etc., change as well. Sleep apnea testing helps to detect abnormal changes that take place during these transitions. Sleep apnea is generally worse during REM sleep, so watching the patient for abnormalities while in REM is particularly important.