Sleep Deprivation and Depression

Normally, depression frequently is thought to cause poor sleep. However, I saw via Medscape that at the 50th annual meeting of the American College of Neuropsychopharmacology, Dr. Meerlo discussed some interesting research findings. In his study, he sleep deprived rats for various lengths of time and measured their brain structure and chemical responses. One day of sleep restriction did not seem to have a dramatic effect. But when they sleep deprived them for 1 week to 1 month, they saw brain changes that looked very similar to those changes in depression.
Also, it took a surprisingly long time for the rats to recover. After one week of restricted sleep, the rats needed almost a week of normal sleep amounts before the brain changes normalized. This suggests that catching up on lost sleep during the weekends may not be sufficient.
Dr. Meerlo concluded that restricted or disrupted sleep over a prolonged period of time may be a causal factor in developing depression, not just a symptom of depression.

Insomnia and COPD

Insomnia is a common sleep disorder - some studies suggest it is the most common one, even more so than sleep apnea. COPD is a lung disease more commonly known as emphysema. Dr. Budhiraja and others published a paper in the March edition of the Journal Sleep about the prevalence of COPD and insomnia. They studied patients with COPD with home sleep studies called actigraphy and had them fill out sleep diaries. No laboratory sleep studies were done, which could be an important limitation to interpreting the study's results.

The results showed that insomnia occurred in 27.3% of the study participants, almost three times the prevalence in the general population (estimated to be 10%). Insomnia was more common in those that were currently smoking, and in those that reported feelings of sadness or anxiety. Insomnia was less common in those receiving oxygen, whether continuously or intermittently. Excessive daytime sleepiness was higher in patients with insomnia. Interestingly, there was no association between COPD severity and insomnia. Some studies have shown that insomnia is more common when COPD patients use their inhalers. However, the results of this study showed that insomnia was not more common in those that used inhalers for their COPD.

In discussing the results, the study authors noted that the insomnia prevalence would have been even higher in those with COPD had they included more females (the patients were all at a VA, which is mostly men), and if they allowed patients with depression to enter the study. Another issue that could be affecting insomnia is that sleep apnea and periodic limb movement disorder can cause insomnia, but would be missed by the home studies used in this study. A lab-based sleep study would have picked that up.

Currently, it is difficult to improve the quality of life in patients with COPD, but improving sleep quality may help. Quitting smoking and using oxygen at night may improve sleep quality enough to boost quality of life.

Heart Rate Variability, Sleepiness, and Sleep Deprivation

Measuring sleepiness is difficult. In the sleep lab, we measure it by timing how quickly someone can fall asleep when attempting to nap. Sleepiness can affect our ability to drive, operate other heavy machinery, and perform complex mental tasks. The sleep field is working on a way to measure sleepiness and its affect on performance. If that could be done relatively easily, then we could determine who might be dangerous on the road, for example. Researchers are looking for the equivalent of the breathalyzer for sleepiness / performance impairment.

Researchers have noticed that the variability in heart rate (HRV) is associated with sleepiness. In the March 2012 Journal Sleep, Dr. Chua and colleagues studied the HRV in sleep-deprived subjects and compared it to a standard measure of mental performance. HRV is determined by a computer program that analyzes the beat-to-beat changes in the heart as measured by an EKG. Subjects were kept awake for 40 continuous hours and the study results showed that HRV correlated with measurements of mental performance.

The authors concluded that EKG-derived measures could possibly be used to determine a person's sleepiness level. However, one problem with measuring sleepiness in this way is that it does not determine absolute level of sleepiness. You would have to determine the normal HRV in each person when they were completely rested before you measure it when they might be sleep deprived. Also, it is not known whether the HRV can determine sleepiness on a moment-by-moment basis. Finally, other factors can affect HRV, like cardiovascular disease and certain medications. Therefore, more research will be needed before HRV can be successfully used to measure sleep-deprived mental performance.

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.