Obstructive Sleep Apnea Treatment With a Nerve Stimulator

Back in January of 2011, I posted about a device developed to treat obstructive sleep apnea (OSA) that could potentially replace CPAP. It's an implantable stimulator that causes the tongue to thrust forward, preventing it from collapsing backwards and blocking off the throat.

In the November edition of the Journal Sleep, Dr. Eastwood and others did a study on 21 patients with moderate to severe OSA that had failed CPAP therapy. They monitored the patients for 6 months and had repeat sleep studies to determine its effectiveness. The results showed that the nerve stimulator did decrease OSA severity and daytime sleepiness. It also improved some aspects of their sleep architecture and daytime functioning. Adherence to the device was high and it was felt to be safe with a low complication rate.

When looking at the details, the device reduced the OSA severity by 55% - from an average AHI of 43.1 to 19.5 at 6 months. But an AHI of 19.5 is considered to be a moderate amount of OSA, with 5 or less being ideal. Also, the device worked better in patients that were thinner than those that were heavier, which makes anatomical sense.

This was a small study with no control group. It will be interesting to see the results from larger trials and for a longer follow up period. One day, this device could be a good alternative to those who have failed CPAP therapy.

CPAP Can Reduce Metabolic Syndrome

Metabolic syndrome occurs when three or more of the following are present: Elevated blood pressure, elevated fasting blood sugar, increased waist circumference (think belt size), low HDL level (the good cholesterol), and high triglycerides. The metabolic syndrome increases risk for heart disease, stroke, and diabetes. In the December 15th, 2011 edition of the New England Journal of Medicine is an article about the effects of CPAP on reducing the metabolic syndrome. The study authors explain that metabolic syndrome is present in 70-80% of patients with obstructive sleep apnea (OSA). Of course CPAP treats OSA, but its effect on metabolic syndrome is not clear.

This study is high quality, as it was a double-blind, placebo-controlled, randomized, crossover design in 99 patients who received three months of either CPAP or sham CPAP, with a one month washout period between interventions. The results showed that real CPAP, when compared to sham CPAP, was able to significantly reduce body mass index, waist circumference, blood pressure, glycosolated hemoglobin (a marker of blood sugar), triglycerides, total cholesterol, and LDL (the bad cholesterol). The author explains that OSA causes dips in oxygen levels that can cause the release of certain fat-inducing hormones and damage the lining of blood vessel walls. These changes could increase the risk for metabolic syndrome, and CPAP appears to prevent this based on the study results.

I wonder if the improvement in many of the factors was due to the weight loss, rather than just the CPAP. In other words, reducing weight can improve blood pressure, lipid values, and blood glucose values. CPAP does not directly cause weight loss, but it can improve energy enough to allow patients to exercise more. They also might not eat as much food, since some patients use food to increase energy. With more energy from CPAP use, they might not eat as much.

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.