Wednesday, April 22, 2015

Obstructive sleep apnea and tooth wear

In my practice, I see lots of patients with excessive tooth wear, or irreversible loss of the tops of the teeth. It gets more common with age. It's not always due to teeth grinding - it can occur from eating certain foods, especially those high in acidity. This study looked at the association between tooth wear and obstructive sleep apnea (OSA). This was a study done in a private dental clinic in Spain, and patients diagnosed with tooth wear each had an overnight home sleep study to assess for OSA. The results showed that the prevalence of OSA was three times higher in patients with tooth wear. And there was a positive correlation between OSA severity and tooth wear, meaning the more severe the OSA, the more severe the tooth wear. The relationship was not diminished after controlling for body mass index, age, and gender.

The study authors speculated that there could be a common mechanism behind the OSA and tooth wear, such as arousal from sleep contributing to tooth clenching or grinding. The study authors also pointed out that the association between OSA and tooth wear could be coincidental, as both conditions become more prevalent with advancing age.

Finally, the study authors recommended that dentists consider referring patients with tooth wear to their primary care provider or sleep doctor for evaluation of possible OSA.

Wednesday, April 15, 2015

Sleep apnea and high blood pressure

Another post about obstructive sleep apnea (OSA) and high blood pressure (HTN). This study is a meta-analysis of observational studies and randomized controlled clinical trials. The study authors studied patients with resistant HTN, meaning blood pressure that was not responding to multiple medications. The study participants also had OSA.

I don't have access to full article, only the link above and the abstract. The results suggest that those patients with the highest blood pressures had the greatest reduction in blood pressure after using CPAP therapy. The study authors concluded that untreated OSA may be why some patients' blood pressure just won't come down with multiple medications.

The results from this study are not new, but do provide more evidence of the importance of screening patients with resistant HTN for underlying OSA. In my community, primary care doctors have been doing this for years already. However, this may not be the case in other medical communities around the country.

Wednesday, April 8, 2015

Blood pressure and sleep apnea

Several research studies have linked high blood pressure (HTN) to obstructive sleep apnea (OSA). The etiology is not clear, however. With OSA, there is sleep disturbance from brief awakenings, thought secondary to adrenaline release that is triggered when breathing resumes. Also, oxygen level reductions, called desaturations, could lead to elevated blood pressures. Respiratory events that are detected during a sleep study have specific scoring criteria - the event has to last at least 10 seconds and result in either a brief arousal from sleep and / or an oxygen desaturation.

This study sought to determine which types of respiratory events were most likely to result in HTN. The researchers followed 2040 participants and used sophisticated statistical models to study the sleep study results and blood pressure measurements. Results showed that those respiratory events with at least a 4% oxygen desaturation were most consistently associated with HTN. Interestingly, the other sleep study measurement that correlated with HTN was periodic limb movements that resulted in brief arousals from sleep.

Wednesday, April 1, 2015

CPAP use after weight-loss surgery

Obstructive sleep apnea (OSA) and obesity are related. Weight loss can improve OSA, sometimes enough to eliminate it altogether. However, if OSA is severe, weight loss alone is often not enough to cure OSA.

Most patients who undergo weight loss surgery have OSA, and most use CPAP prior to weight loss surgery. Unfortunately, most patients discontinue their CPAP use after weight loss surgery. This study assessed long-term CPAP use in 21 patients who had undergone gastric banding. Results showed that body-mass index significantly increased by 6.8 in those patients who did not use their CPAP after weight loss surgery. And BMI dropped by 1.8 in those patients that were adherent to CPAP therapy after weight loss surgery.

Another important point is that OSA persisted in almost all of the patients who underwent the surgery, despite the substantial weight loss (average 121 pounds lost). And, after 7.2 years of follow up, the majority of patients had gained back some weight (22 pounds).

So the data in this study suggest that CPAP adherence for the long term may help with weight loss maintenance. Remember this is a small study though. Other confounding factors could contribute to reasons why some patients chose to keep using CPAP. For instance, some may have continued only because using CPAP made them sleep better or have more energy. And that increased energy could have helped them keep exercising, which may help maintain weight. Or those that kept using CPAP may have adhered better to diet restrictions.

In the end, follow up with the sleep medicine specialist is important after weight loss surgery. In that way, post-operative OSA severity can be assessed after the first year. Then, the patient and sleep medicine physician can discuss the pros and cons of continuing CPAP therapy if necessary.

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 analogy...it 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.