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.

Chronic Cough and Obstructive Sleep Apnea

There is a review article in the Journal of Clinical Sleep Medicine about a relationship between chronic cough and obstructive sleep apnea (OSA). Chronic cough is a significant problem, and in non-smokers, is usually due to post-nasal drip (now called upper airway cough syndrome), gastroesophogeal reflux disease (GERD), or cough-variant asthma.

The authors discussed a couple of cases where patients with chronic cough were diagnosed with OSA, treated with CPAP, and their chronic cough improved dramatically. The authors speculate that OSA could be associated with chronic cough by being related to the reasons patients get post-nasal drip, GERD, or cough-variant asthma. GERD and OSA have already been associated by prior studies. OSA can result in inflammation of the upper airway, which could contribute to post-nasal drip. Finally, studies are showing a relationship with asthma and OSA. Also, OSA by itself has been associated with airway inflammation, be it from repetitive oxygen drops, direct trauma from vibrating tissue, or from the bloodstream. This inflammation could result in chronic cough. So if you have a chronic cough, talk to your doctor about being evaluated for obstructive sleep apnea.

Sleep Duration, Disinhibited Eating, and Weight Gain

Studies have been linking short sleep duration and weight gain in children and adults. Increased food consumption is thought to be responsible for this - short sleepers have more time awake to eat, especially at night. However, there is great variability in weight gain amongst short sleepers. A study was published in the Journal Sleep about short sleepers, disinhibited eating habits, and weight gain. Disinhibited eating examples include eating in response to a negative mood (emotional eating), overeating when others are eating, not being able to resist eating, and overeating because the food tastes good, rather than because of hunger.

The study participants consisted of 276 adults, aged 18 - 64 years old, who were followed for six years. They were nonsmokers, had stable body weight over the 6 months preceding testing, and have no metabolic disease (like diabetes or high blood pressure) or be on any medication that could confound the results. The participants were asked how many hours they slept per night, and divided into short sleeper (<6 hours per night), average sleeper (7-8 hours per night), and long sleeper (>9 hours per night). Disinhibited eating behavior was assessed via a validated eating questionnaire.

The results showed that those participants with high disinhibited eating patterns significantly increased their risk of overeating and gaining weight if they also had short sleep duration. As expected there was a relationship between increased total amount of food eaten and high disinhibited eating pattern. Interestingly, this relationship was only seen in short sleepers, and not seen in average and long sleepers.

Sleep Timing, Weight Status, and Activity Patterns in Children

Studies have indicated a relationship between short sleep duration and obesity in children and adults. The cause of the elevated weight in short sleepers is not known. There is relatively little research done on the relationship between the timing of sleep, weight, and activity patterns. In the Journal Sleep is a study about this topic. The researchers classified sleep timing as early to bed / early to rise, early to bed / late to rise, late to bed / early to rise, and late to bed / late to rise. They studied Australian children ages 9 - 16 years old, and surveyed their sleep habits, physical activity, and measured their weight, height, and waist circumference.

The results showed children who were late to bed / late to rise were 1.5 times more likely to be obese, 1.8 times to have too little physical activity, and 2.9 times more likely to have excessive use of computers and television (a.k.a. screen time) than the early to bed / early to rise group. Interestingly, the greatest differences in the above measurements were between the late to bed / late to rise and early to bed / early to rise groups, which slept the same amount per night. There was little difference in early to bed / late to rise and late to bed / early to rise, which had an average total sleep time difference of over 2 hours per night. This is contrary to the prior studies that suggest sleep duration is linked to obesity. The results from this study imply that it is the timing of the sleep, not the sleep duration, that is associated with obesity.

Some advocate that adolescents be allowed to stay up late and sleep in, including later school start times. However, this might make the obesity problem even worse, according to the study results. If anything, this study suggests that children should be put to bed earlier and gotten up earlier.