Anatomy vs. Physiology

There is an article in the December edition of the Journal of Clinical Sleep Medicine about the clinical usefulness of the way many sleep clinicians grade the crowding of the back of a patient's mouth. It's called the Mallampati score and is based on the way Anesthesiologists judge how easy someone might be to intubate.

The Mallampati grade is done by looking at the space in the back of the mouth with the mouth open and tongue out. In this case, it is done when the patient does not say "Ahhhh." I use a modified Mallampati grade like this...

The higher the grade, the more crowded the back of the throat. In general, the higher the grade, the more likely there will also be snoring and/or obstructive sleep apnea (OSA). It's nice to have a physical feature that corresponds to risk of OSA because symptoms alone are not able to predict if OSA is present. In fact, this article quotes some interesting stats from another study - in patients without OSA, 56% snore, 67% report choking while asleep, 35% have witnessed apneas, and 68% report waking unrefreshed - all symptoms usually seen in OSA.

The study done in this edition of the Journal of Clinical Sleep Medicine attempted to determine if a higher Mallampati grade ruled in severe OSA or if a lower Mallampati grade ruled out any OSA. The results showed that Mallampati grade is significantly associated with sleep apnea severity. However, the Mallampati grade only explained 1.7% of the variability of the severity of the OSA. In other words a high Mallampati grade alone can not be used to rule in severe OSA and a low Mallampati grade can not rule out OSA.

This makes sense to me, as anatomy, or the degree of crowding in the back of the mouth is only part of the reason OSA occurs. In some patients, their throat has a predisposition to collapse during sleep, no matter how crowded their throat is. It's analogous to body builders.

You might think that someone who wins body building competition would be strong. However, they are not power lifters, as body builders focus more on the visual appearance, rather than the strength of their muscles. By the way, the movie Predator is one of Arnold's best. Yes, Terminator is good too.

Sleep Symptoms and Metabolic Syndrome

An article in the December issue of the Sleep Journal has received media attention, so I thought I would summarize it here.

Metabolic syndrome is defined as having three or more of the following: elevated blood glucose, increased waist circumference, high blood pressure, increased triglycerides, and low HDL (the good cholesterol). It is estimated that 20% of us have the metabolic syndrome.

The authors of this study assessed over 800 people ages 45 to 74 over a three year period to see if they developed the metabolic syndrome and if it was associated with any sleep symptoms. They used a subjective questionnaire to assess insomnia symptoms, loud snoring, gasping at night, and/or nighttime choking. Sleep duration was not assessed. Almost 300 of the study participants volunteered to have a home sleep study (Resmed's ApneaLink) at the end of the three years.

Over the three year span of time, 14% developed the metabolic syndrome. The sleep symptoms that were statistically related to metabolic syndrome were difficulty falling asleep, unrefreshing sleep, loud snoring, and elevated score on the ApneaLink home sleep study. There was no interaction with race of gender. Loud snoring was most predictive, more than doubling the risk of developing metabolic syndrome. As expected, insomnia syndrome did not raise the risk of metabolic syndrome.

The study authors were not able to tell if the patients who claimed loud snoring also had the elevated sleep apnea severity as measured by the ApneaLink. This would have been helpful because the authors concluded that loud snoring by itself is a risk factor in developing metabolic syndrome. I'm not convinced that loud snoring without sleep apnea is physically dangerous to patients.

It was interesting that difficulty staying asleep did not significantly raise the metabolic syndrome risk, but difficulty falling asleep did. This goes against my clinical experience of how many sleep apnea patients sleep - most fall asleep easily, but just can not stay asleep. The authors suggested that the difficulty falling asleep could be due to emotional and/or physiologic hyperarousal, which could be due to increase nervous system activity and elevated cortisol levels. These have been linked to insulin resistance and the metabolic syndrome.

For me, the conclusion from this study is that you should seek a sleep evaluation from your doctor if you have loud snoring and/or difficulty falling asleep.

Snoring and Obstructive Sleep Apnea

In the October (yes, I am behind) edition of the Journal of Clinical Sleep Medicine, there is an article about how snoring correlates with the severity of obstructive sleep apnea (OSA). Snoring occurs in 25% of women and 45% of men, and is the most common symptom of OSA. Snoring is considered a "cosmetic" issue and is not associated with other illnesses like high blood pressure, cardiovascular disease, stroke, or metabolic syndrome, the way OSA is.

This study was the first one to use an objective measurement of snoring intensity in a large (>1600) group of patients to determine the relationship between OSA and snoring loudness. They measued snoring during a sleep study with a digital sound meter. In this study, there were more males than females. Men were older, heavier, and had larger neck circumferences than women.

The results showed that men had louder snoring than women (big surprise, huh?), and this was consistent across all sleep stages, body positions, and weight. Snoring was louder among those that were heavier, had larger neck sizes, and when sleeping on the back, regardless of gender. Snoring was more common in non-dream (NREM) than dream (REM) sleep. As expected, snoring got louder as the OSA got more severe. I've told patients about this observation in my clinical practice, and now there is objective proof.

Geneitc Link and Sleep Disorders

There is an article in the October 26th issue of Neurology where researchers studied normal sleep and sleep-deprivation, and determined if participants had a certain gene variant (DQB1*0602). Patients with that gene variant were sleepier and more fatigued while sleep-deprived or even while fully rested. These individuals also woke up more often at night and spent less time in deep sleep than those without the gene variant. However, there was no difference on tests of memory and attention, or in their ability to resist sleep during the day.

The authors explained that their findings mean there might be a genetic biomarker to predict how people will respond to sleep deprivation. This has significant health consequences and affects millions around the world. It may be particularly important in those work night shift, travel frequently across multiple time zones, or just don't sleep enough due to multiple work and family obligations.

This gene variant has already been implicated in narcolepsy, a sleep disorder characterized by excessive sleepiness, despite adequate amounts of sleep at night.