I am about to undergo testing for sleep apnea. I've been told that I will be monitored from 8pm to the next morning. I am anxious about this, because I have so much trouble sleeping anyway, and I can't imagine sleeping while I am connected to measuring devices or if someone is watching me. Would you tell me what this procedure involves and what are the chances of a correct diagnosis if I am that anxious?

Joan

This is a very common concern. I can assure you, though, that while your sleep may be even more erratic than usual, you will almost certainly sleep long enough to obtain a valid study.

A little background would be nice for our readers. Sleep studies (polysomnographs) are ordered by a doctor to test for a treatable sleep disorder such as obstructive sleep apnea (OSA), a condition in which the patient's airway becomes blocked during sleep. The tongue, soft palate, or both may "fall backward," blocking the airway. Breathing may become dangerously shallow or may stop altogether. (Apnea means "no breath.") The patient wakes, just enough to take a few breaths, then falls back to sleep. This can happen many times per hour, destroying the quality of sleep.

A less severe form of this problem is upper airway resistance syndrome, in which sleep is again fragmented, but unlike OSA, breathing rarely stops completely. Nevertheless, patients with upper airway resistance syndrome still suffer from extreme daytime sleepiness due to poor sleep quality.

During a polysomnograph, you will be monitored for brain waves (electroencephalogram), heart rate and rhythm (electrocardiogram), eye movements, blood oxygen content, muscle activity and respiratory activity. The goal of a sleep study is to learn something about sleep efficiency and whether you have breathing problems during sleep. If you do, how severe are they? Does your blood oxygen content drop to dangerous levels? Do you develop dangerous alterations in heart rhythm due to your breathing difficulties?

Let's focus on the brain waves for a moment. The brain itself is little more than a lump of neurons (nerve cells), blood vessels and cells that serve a supportive function for the neurons. Neurons communicate with one another, and with the rest of the body, by electrochemical impulses. A tiny electrical charge is conducted down the length of a neuron. Whenever an electrical charge moves, electromagnetic waves are emitted. An electroencephalogram (EEG) measures the electromagnetic waves emitted by the brain as a result of neuronal electrical activity.

Sleep is more complex than most folks realize. It can be described as consisting of alternating REM (rapid eye movement) and NREM (non-REM) phases. NREM sleep is further divided into four stages based on the type of brain waves detected by EEG. By measuring eye movements and EEG, a sleep study can thus characterize how much time you spend in these phases of sleep.

This is significant for two reasons. By measuring the time spent in different phases of sleep, we can determine sleep efficiency. Measurement of EEG and eye movement answers a more obvious concern -- and this speaks directly to your concern: Will I sleep at all during the test? You can't fake the EEG patterns typical of deep sleep, and you can fake REM only with difficulty and practice. Thus, the sleep study will certainly demonstrate whether you slept at all during the study.

Keep this in mind when your doctor tells you the results of the study. It is fairly common for a patient to tell me, "That study was a real waste. I didn't sleep at all!" But that's only the patient's subjective opinion; the sleep study tells a different story. How could a patient be so incorrect? Unless you dream (and remember your dream), you are conscious only of your waking moments. If your sleep is highly fragmented, these waking moments will be scattered throughout the night, giving you the impression that you "never" slept. The truth of the matter may be that you slept all night -- but poorly!