Wednesday, March 25, 2015

Sleep and learning

Although the exact details are unknown, researchers believe that sleep is helpful in integrating and strengthening new memories. When I was a fellow, it was thought that this occurred mainly in dream (REM) sleep. Here is an article that studied the effect of slow wave sleep (SWS), a deep non-dream state, on memories related to fear. Apparently, studies have shown that memories can be reactivated during SWS by a reminder cue like odors or sounds experienced during SWS.

In this study, researchers used a conditioning procedure in humans to elicit a fear response. Specifically, they repeatedly paired a neutral sound with a mild electrical shock to the wrist of the participants. After enough pairings, the neutral sound would cause a measurable fear response in the participant, even without the electrical shock. In other words, the participant learned that the neutral tone meant the electrical shock was coming. After this conditioned learning, the participants slept for 4 hours because the first 4 hours of sleep are dominated by SWS. The second half of sleep is dominated by REM sleep, and the researchers wanted to isolate the effects of SWS.

One way to eliminate the learned fear response that has become paired with a conditioned stimulus like a neutral tone is to repeatedly expose the subject to the neutral tone but without the electrical shock. Over time, the neutral tone will stop causing the fear response as the subject learns that the electrical shock no longer is associated with the neutral tone. So in the study, the researchers played the neutral tone without the electrical shock during SWS. Results showed that this was able to attenuate the fear response. And this was compared to other subjects that received a different tone than the neutral tone and in those that received no tones at all. Finally, exposure to the tones in SWS did not appear to negatively affect sleep architecture or sleep quality.

So what does all this mean? Well in psychology, when someone has pathological fear or post-traumatic stress disorder, one effective treatment is to repeatedly expose the patient to what they fear, so that their fear response gradually attenuates. It's very challenging therapy for patients, because they have to consciously subject themselves to their fears. But, as this study suggests, maybe patients with pathological fear can be exposed to the feared stimulus during SWS, and not have to experience it consciously in order to reduce the fear response. Here's an would be like going from having your appendix taken out while awake to having it taken out under anesthesia.

Wednesday, March 18, 2015

Sleep apnea, motor vehicle accidents, and CPAP therapy

There are recent meta-analyses showing higher risk of motor vehicle accidents (MVA) in those with obstructive sleep apnea (OSA), and a lower risk of MVA with CPAP therapy. However, the conclusions from these studies is somewhat limited due to possibly faulty research designs. In other words, it's still uncertain how much risk OSA imparts and if CPAP really reduces that risk. However, this study, recently in the Sleep Journal, set out to determine just that, using a well designed protocol. It was a retrospective study of almost 1500 drivers in Sweden. The results showed that there was a 2.5 fold increase in risk of MVA in patients with OSA. The risk was highest in older drivers. Also, risk was highest in those with high subjective sleepiness, but the risk did not depend on OSA severity. And the incidence of MVA was reduced by 70% among patients that used their CPAP at least 4 hours per night. Interestingly, risk of MVA was increased by 54% among those that used CPAP less than 4 hours per night.

The authors concluded that because CPAP therapy can improve sleep quality and overnight oxygenation, it could improve alertness and driving performance - leading to less MVA's.

Wednesday, March 11, 2015

Sleep duration and stroke risk

I've blogged here and here about stroke risk and sleep duration. The data suggest a U-shaped curve with regards to stroke risk and amount of sleep. This means that those who are short or long sleepers are at increased risk.

This study also examined stroke risk and sleep duration. The data was from a larger cohort study and included over 16,000 participants. Sleep duration and sleep quality were assessed with a self-reported questionnaire. The researchers divided up the participants into short sleeper (<6 hours per night), average sleeper (6-8 hours per night), or long sleeper (> 8 hours per night). Of note, this is an arbitrary definition, although generally agreed upon in our field.

Results showed a J-shaped curve, meaning that longer sleepers had a 46% higher risk of a stroke after adjusting for the usual cardiovascular risk factors. Of note, this result was only significant for those aged 63 and older. And the association remained even if the participant reported sleeping longer, but had good sleep quality.

Short sleepers had an 18% increased risk of stroke, but this was not statistically significant. Both groups were compared to the stroke risk of average length sleepers.

The authors concluded that long sleep duration may be an early sign of increased stroke risk, particularly among healthy people.

Wednesday, March 4, 2015

Later school start times for teenagers

School start times are a hot issue these days. Particularly, letting teenagers start school later, to match their natural pattern of sleeping in later than younger kids. This report is about a survey done at the University of Michigan where researchers asked parents how they felt about later school start times. Below is a figure from the report that shows some of the results of the survey.

Most of the parents (88%) said their teens currently have a start time before 8:30 a.m. Among these parents, 27% of parents would support a school start of 8:30 a.m. or later only if it did not impact the school budget, and 24% would support a later start time regardless of impact on the school budget. Less than one-half (49%) of the parents do not support a later school start time.

Wednesday, February 25, 2015

Sleep duration in American teens

On the heels of last week's post about new sleep duration recommendations, this post is about an article in the journal Pediatrics about the changes in sleep amounts among teens in the United States from 1991 to 2012. The participants were 270,000 8th, 10th, and 12th graders involved in a larger survey. The researchers asked the participants two questions about sleep duration. One was how often they got less 7 hours or at least 7 hours of sleep. The other question was how often the teen felt they got enough sleep per week.

Epidemiological studies show that almost a third of teens don't get enough sleep. The reasons are not known, but researchers speculate that internet, social media, and increased competitiveness of the college admissions process are contributing. And, in last week's blog, I posted a table that recommends 8-10 hrs per night for 14-17 year olds.

The results of the current study showed that self-reported sleep duration in teens has decreased over the past 20 years. The largest decrease was in 15 year olds. Although the data show that sleep duration declined across all age groups and major socio-demographic subgroups, results showed that female students, racial/ethnic minorities, and students of lower socio-economic status (SES) reported getting at least 7 hours of sleep less often than male subjects, non-Hispanic white subjects, and students of higher SES.

Wednesday, February 18, 2015

New sleep duration recommendations

Here is an article that discusses the National Sleep Foundaion's latest sleep duration recommendations. One thing that caught my attention is that sleep duration for adults is broken up into 3 categories - young adult, adult, and older adult. This makes sense to me from a physiological perspective, as older adults may not need as much sleep as 20 somethings.

Wednesday, February 11, 2015

Nasal surgery and CPAP

Most of my patients with obstructive sleep apnea (OSA) report they are "mouth breathers" at night. Because of that, they often think they should use a CPAP mask that covers their nose AND mouth...the full face mask. Full face masks often leak excessively, especially for side sleepers. I find that most of the time, my patients do well with a mask that just covers their nose or goes right in their nose (nasal pillows). But I have a small segment of patients who really struggle to breathe just through their nose. Almost all of these patients have daytime nasal stuffiness as well. Often, airflow through their nose is not improved with by-mouth medications or nasal sprays. In these cases, patients can opt to use the full face mask, or consider surgical therapy to improve nasal airflow. If the Ear, Nose and Throat (ENT) physician determines there is significant anatomical obstruction, then surgical therapy may improve nasal airflow enough to allow the patient to utilize an over-the-nose mask, instead of the full face mask.

Here is a study supporting my clinical experience. It's a meta-analysis of current literature. After examining past studies, the authors concluded that nasal surgery to relieve obstruction resulted in an average lowering of CPAP pressure by 2.66 cwp. Regardless of nasal surgery type, CPAP pressures were lower on average 1.9 cwp between preoperative and postoperative periods. The greatest difference was in those patients undergoing combined septoplasty with turbinoplasty. Finally, overall CPAP use increased after nasal surgery, possibly due to overall lowered CPAP pressures. The study did not mention changes in mask styles after surgery, such as from full face mask to nasal mask. This change alone, even without reduction in CPAP pressure may improve CPAP adherence.