Depression and obstructive sleep apnea

Depression is a common disorder that exists along with obstructive sleep apnea (OSA). The exact relationship between the two disorders is not known. OSA may contribute to depression due to sleep loss, sleep disruption, and cognitive effects of intermittent low oxygen levels to the brain. Also, weight gain and sleep disruption from depression could exacerbate OSA. Some, but not all of my patients report that their depression gets better with treatment of OSA.

This study is a meta-analysis of research looking at the effects of CPAP and oral appliances on depressive symptoms (as obtained by depression questionnaires) in adults with OSA. The results showed small improvements in depressive symptoms with OSA treatment. The greatest benefit was seen in those patients with the worse depression scores at baseline.

Insomnia and mortality

Chronic insomnia is a frequent problem, and several studies have attempted to link insomnia with medical problems, even death. However, it's not clear from these studies that the relationship is as stated. One methodology problem with these studies is the fact that most of them define insomnia based solely on the research subjects' description of their sleep quality. In other words, secondary causes of insomnia are not ruled out with objective testing like sleep studies. This abstract is about research done on subjects with chronic insomnia. I don't have access to the actual article, so my analysis of the study is limited. I can't tell from the abstract if the research subjects had secondary causes of insomnia ruled out with sleep studies.

Researchers used data from a community-based cohort and categorized subjects into having either persistent, chronic insomnia, only intermittent insomnia, or no insomnia. The researchers defined persistent based on the subjects' description of their sleep quality over a six year period. They then determined when the subject died for up to a 20 year period. The researchers also examined levels of a marker of inflammation called serum C-reactive protein (CRP). There were 1409 research subjects - 249 with intermittent insomnia and 128 with persistent insomnia. The results showed that the subjects with persistent insomnia were 58% more likely to die than those without insomnia. Those with intermittent insomnia were not more likely to die than those without insomnia. Of note, most of the deaths were cardiovascular. CRP levels were higher in those with persistent insomnia than in those with either intermittent or no insomnia. The authors noted that CRP levels were associated with increased mortality by themselves. However, adjustment for CRP levels did not notably change the association between persistent insomnia and mortality. Also, the results were adjusted for confounders such as age, sex, body mass index, smoking, physical activity, alcohol, and sedatives.

Obstructive sleep apnea and exercise capacity

This study is a cross-sectional evaluation of the relationship between obstructive sleep apnea (OSA) and exercise capacity. According to the authors, how OSA affects exercise capacity is not clear, as prior studies have conflicting results. In this study, researchers did sleep studies on participants and put them into two groups. Those with no or mild OSA, and those with moderate or severe OSA. They then measured their exercise capacity and compared the results. The main finding was that OSA was associated with decreased exercise capacity. And more severe OSA was associated with worsening exercise capacity. The mechanism behind why OSA would affect exercise capacity is not clear. The authors speculate that it could be due to changes in energy pathways, changes in muscle fiber structure, and/or changes in blood vessels in muscles - thought to be a result of low oxygen levels associated with OSA.

Smoking and sleep

This article describes research about reducing cigarette smoking in your sleep. The study in the article involves using a psychological concept of learning called respondent conditioning - think of Pavlov and his dog, at outlined in this Wikipedia article. The study participants were all smokers who expressed desire to quit. Researchers paired the smell of cigarettes with a foul odor when participants were asleep. Supposedly, the participants unconsciously associated the foul smell with the smell of cigarettes and ended up smoking 30% less. There was no smoking reduction in participants that were exposed only to cigarette smoke when asleep or if the participants were exposed to both smells, but while awake.

Two other interesting points about this study. The first one is that the participants did not remember the smells they were exposed to in their sleep. Also, it appeared that a light stage of non-dream sleep was was the most effective stage of sleep that was associated with reduced smoking. The authors concluded that conditioning can occur in sleep and that this technique may be used in other addictions.