Sunday, December 26, 2010

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.

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