Lorna Cornelius understood why she was tired. The Malad, Idaho, woman has lupus and that's just one of the symptoms.

She was surprised when her pulmonologist suggested a sleep study. Something else might be going on as well, he told her.

It's not uncommon for sleep disorders to co-exist or even be masked by other conditions. It turned out she also has sleep apnea, her sleep interrupted as many as 10 times an hour.

Some sleep disturbances are easy to diagnose; others may require an overnight sleep study, called a polysomnogram. The patient is hooked up to surface electrodes and other measuring tools that allow a technician to monitor what happens during sleep. Then it's off to bed in a private room. During the night, as you sleep, your respiration, brain activity, oxygen level, heartbeat, eye movements and more are monitored.

An electroencephalogram measures and records alpha, beta, theta and delta brain wave activity. The electromyogram records muscle activity such as face twitches, grinding teeth and leg movements. The electro-oculogram records eye movements, important to determining sleep stages. An electrocardiogram records heart activities, while a nasal airflow sensor records breath temperature and airflow. Belts around the chest/abdomen record breathing depth and apnea or hypopnea events. Oxygen saturation is measured and a video records body positioning and movement. Even the sound of snoring is captured.

If apnea is confirmed, a technician may begin CPAP treatment sometime during the study to see if it helps and to adjust air pressure level.

Not all sleep studies occur at night. People who work at night might have a sleep study done during the day. Or an individual may have a "Multiple Sleep Latency Test" to measure the degree of daytime sleep tendency or sleepiness. Methods vary some, but it's common to monitor a series of naps, each less than 20 minutes, timed at intervals. The test helps determine how long it takes to fall asleep during naps and then records the characteristics of the naps, such as if REM stage sleep occurs.

It's used to diagnose people with narcolepsy, a form of uncontrollable daytime sleepiness, adjust medication or quantify the degree of sleepiness in a patient, such as in the person with sleep apnea who is still tired despite CPAP treatment.

Often, a primary care physician can manage treatment quite well once diagnosis is made, sleep experts say. But it may take someone with sleep expertise to get an accurate diagnosis.

A sleep study may show sleep is not as bad as the individual believes, which is called sleep state misperception. People equate not remembering their dreams with not dreaming and think they don't fall into a deep sleep. But the study may show they did enter what experts call a dream sleep. Those who wake up more in the night are more apt to remember dreams.

If you decide to have a sleep study, be sure the center has someone qualified reading the results. There are lots of centers around, some better than others, sleep specialists warn. And if you happen to get an inadequate study, insurance may not pay for another one.

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E-mail: lois@desnews.com