Brain Waves, Breathing Cycle, Sleep Apnea, and CPAP

Chervin et al have published a study in the February edition of the Journal Sleep about how sleep doctors determine obstructive sleep apnea (OSA) severity and response to CPAP therapy. On a sleep study, we grade the OSA severity by the number of times per hour a patient's airway collapses - abbreviated as the AHI. Often, airway collapse produces an arousal from sleep, seen in the brain wave changes measured on the EEG. Looking at the EEG with just our eyes, however, misses much smaller patterns that are visible only by computer analysis. These smaller patterns have been studied in patients with and without OSA, and researchers note some important differences. It's not known, however, if the brainwave patterns change with CPAP therapy.

The study authors did such an experiment, measuring brainwave changes during a diagnostic sleep study and then during the CPAP calibration study. The results showed that CPAP therapy tended to normalize the brainwaves. This might seem obvious, but remember, these are brainwaves that can only be seen by sophisticated computer software programs. Up until this study, sleep researchers had only suspected that CPAP therapy could change these brainwave patterns.

The implications have more to do with the way we diagnose OSA and how we determine the cause of someone's sleepiness. Currently, since we rely on human eyes to evaluate brainwaves, we miss the more subtle brainwave changes that could be clinically important. It's similar to looking at a tile mosaic from 20 feet versus 1 foot. At 1 foot away, you can see that the piece is made up of hundreds of different tiles, and you couldn't make that out at 20 feet. Anyway, this more detailed analysis of brainwaves could become a more accurate and standardized way that sleep patients are studied in the sleep lab.

Glucose Tolerance in Narcolepsy Patients

Narcolepsy is a sleep disorder that occurs when a small set of cells located deep in the brain die off. Narcoleptic patients have excessive sleepiness and other symptoms. The area of the brain affected is the hypothalamus, which controls basic drives like appetite and sleep. Elevated body weight is a common finding in patients with narcolepsy, and some studies have suggested that problems with glucose (blood sugar) metabolism could be involved. However, it's not clear if it's the narcolepsy itself that could alter glucose metabolism or the obesity associated with the narcolepsy that is responsible.

In the Journal Sleep, Beitinger et al did a study comparing the glucose metabolism of narcoleptics to healthy control patients that had the same body mass index, age, and gender. Their results showed no difference in glucose metabolism in the narcoleptic patients versus the matched controls. This means that the higher rates of glucose metabolism problems seen in narcoleptics are due to elevated weight, not from the narcolepsy itself.

Sleep Duration, Sleep Quality, and Cardiovascular Disease

Epidemiological studies have linked short sleep duration, usually defined as less than 6 hours per night, with cardiovascular disease (CVD). However, it is not know whether short sleep duration itself, or if poor sleep quality with shorter sleep duration accounts for the relationship to CVD. In the Journal Sleep is an article where researchers investigated this relationship in a large study carried out in the Netherlands in the 1990's.

Information on sleep quality and sleep duration was obtained by a survey, not measured via sleep studies. Researchers also assessed educational level, smoking status, physical activity, alcohol and caffeine consumption, subjective health, and CVD risk factor medication via self-administered questionnaire.

The results showed that short sleepers had a 15% higher risk of total CVD and a 23% higher risk of coronary heart disease (CHD) when compared to normal sleepers and after adjustment for relevant co-variables. Those with short sleep duration AND poor sleep quality had a 63% higher risk of total CVD and a 79% higher risk of CHD. Short sleepers with good sleep quality and those with long sleep duration (defined as >9 hours of sleep per night) did not have an increased risk of total CVD or CHD.

The take home message is that the duration of sleep is only part of the problem. Some people don't need 8 hours of sleep. But if you sleep about six hours or less, AND that sleep is broken up or non-restorative, you could have increased risk for cardiovascular disease. You should consider seeing your doctor or consulting with a sleep physician.

Sleep Aids, Mortality, and Cancer

In the British Medical Journal is a study that has received a lot of attention in the press. In this study, the authors looked at over 200,000 patients in Geisenger's Health System, including those who did and did not use sleep aids. Their analyses showed that those that took any type of sleep aid had a significantly higher chance of dying compared to those who did not take sleep aids. And the data showed that the risk of dying was still higher in sleep aid users when controlling for underlying diseases known to increase death, like heart and lung disease. There was also an increased risk of cancer in those that took sleep aids compared to those that did not.

The researchers speculate that increased death rates may occur with sleep aid use because some sleeping pills are lethal if too much is taken at once or if combined with other drugs or alcohol. Some sleep aids increase risk of depression which could lead to suicides. Sleep aids, especially in the elderly, can increase risk of car crashes and falls. Some sleep aids can worsen underlying sleep apnea, which already has a higher mortality rate.