It’s been fun to talk with people suffering from Delayed Sleep Phase over the last couple days. There’s been some questions about shifting sleep phase using light therapy and melatonin supplements. The timing of these therapies depends on whether you want to delay sleep, ie. make it begin later, or advance sleep, making it occur earlier. Once you know that, then you use the Phase Response Curve to see when to use these therapies.
A word of warning: The correct timing is crucial, so it is best to work with a sleep professional if you want to shift your sleep phase. If you use light or melatonin therapy at the wrong time you can cause problems by shifting your circadian rhythm the wrong direction.
Follow this link to the Phase Response Curve on Wikipedia: http://en.wikipedia.org/wiki/File:PRC-Light%2BMel.png
On the horizontal axis you see time, and the sleep period written in. On the vertical axis you see hours of phase advance on the top, and hours of phase delay on the bottom. Bright light is represented by dark purple, melatonin by green. Note that the light curve goes both higher and lower than the melatonin, that is because a much larger phase shift can be achieved with light.
Let’s look at an example. Say an adult is unable to sleep until 2am, but must get up for work at 7am. Getting 5 hours of sleep each night is not enought for her. She would like to sleep from 11pm to 7am, but is just not sleepy. Using the Phase Response Curve, she begins using light therapy each morning when she gets up for the day. She also takes some melatonin 6 hours before bed. These combined therapies allow her to feel sleepy at 11pm, and fall to sleep easily. Now she can get a full night’s sleep, and all the benefits of sufficient sleep.
An ‘Owl’ is someone whose body clock is set to sleep later than average, and a ‘Lark’ is someone whose set to sleep earlier than average. It is your inherent melatonin rhythm and temperature rhythm that determine when you sleep.
Being an Owl or Lark can impact how well you do with different schedules. Generally speaking, Owls do better with later schedules and shift work like graveyard. Larks are the ones you’d want to open the shop in the morning. It’s important to know that alertness fluctuates over the 24 hours in almost the same curve as temperature. As your temperature drops you are less alert and more sleepy. If you get into bed and try to sleep before your body is ready, you may experience this as insomnia. About 10% of chronic insomniacs actually are Owls, and if they go to bed later have no problem sleeping.
To determine if you are an Owl or Lark you can do the Horne-Ostberg Morningness-Eveningness questionnaire, which was developed in 1976. You can find a modified version of it online at http://web.ukonline.co.uk/bjlogie/test.htm.
This information can help you develop a lifestyle that best suits your circadian rhythm. If you are not able to shift the time of your commitments, a sleep specialist may be able to help shift your circadian rhythm.
Sometimes people also need to have their daytime sleep tested. There are two main tests, the Multiple Sleep Latency Test (MSLT) or the Maintenance of Wakefulness Test (MWT). In sleep centers the MSLT used primarily, so that’s the one we will discuss here.
The MSLT is conducted the day following an overnight study, and begins 2 hours after waking. Patients should sleep on their regular schedule the night before, and get dressed for the day. The patient lies down in bed, and allows himself to fall asleep. After 20 minutes the nap test is over. The test is repeated every two hours for a total of 4 or 5 naps. The data from all tests is averaged.
The sleep specialist is measuring how long it takes the patient to fall asleep, and whether the patient had REM sleep. This helps assess how sleepy the person is. It is considered normal to fall asleep in 15 minutes, sleepy if sleep occurs in less than 10 minutes. Narcolepsy is characterized by a sleep onset of less than 8 minutes, with 2 sleep onset REM periods. We’ll talk more about narcolepsy in the next post.
First of all, know that almost all people sleep just fine in the sleep lab. Before and during medical school I worked as a PSG tech, so I know this is true from seeing hundreds of people sleep well.
You’ll be asked to arrive at the lab about 7pm. You will work with one staff called a PSG Tech throughout your stay. He or she will show you the bedroom, and hook the testing equipment to you. They will monitor you throughout the night and unhook the testng equipment in the morning. If you need to use the restroom in the night, no problem, simply call out to let the Tech know.
Most sleep labs have bedrooms that look like hotel rooms with a double or queen-sized bed. You are welcome to bring your most comfortable pillow, and a favorite book or movie to enjoy before bed.
Keep in mind the information gathered during the overnight sleep study is so valuable in diagnosing and treating sleep problems that it is well worth it.
What data is collected during the sleep study?
There are thin electrodes placed on your scalp with paste, at the outer corner of each eye, and on your chin. These are used to determine whether you are awake or asleep, and what stage of sleep you are in.
Additional testing equipment includes elastic bands around your chest to measure your breathing effort, EKG pads on your chest to monitor your heart, and electrodes on your legs to monitor leg movements. You will also have a sensor on one finger to measure your blood oxygen level.
From this monitoring equipment physicians can see how your sleep cycles looked, and percentage of each sleep stage. Also can see if you had any sleep breathing or movement disorder, or other more rare sleep disorder.
Next blogpost we’ll talk about ways to be most comfortable during the overnight sleep test.