Obstructive sleep apnea (OSA) is a common breathing disorder, characterised by recurrent partial or complete upper airway collapses during sleep, resulting in sleep disturbance. The disorder can cause daytime sleepiness, headaches and trouble with memory, and is linked to a variety of serious health conditions, such as heart disease.

Of all the risk factors associated with OSA, obesity is a strong contender. It is thought that excessive gain weight leads to an increased tongue volume due to increased fat content that narrows the upper airway, which becomes more susceptible to collapse.

However, while obesity predisposes to, and increases the severity of, OSA, not all obese people develop OSA, and this is not well understood why.

We think that adequate inspiratory tongue movement (i.e how well the tongue moves forward during inspiration) plays a vital role in the prevention of OSA in healthy obese people, by protecting the narrow airway of collapsing. However, whether this tongue movement is altered by tongue fat content is not known.

With these considerations in mind, we examined the effect of upper airway fat content on inspiratory tongue movement during wakefulness in people with and without OSA, using advanced magnetic resonance imaging techniques. We found that people with OSA have a greater tongue volume than controls, but not a higher percentage of tongue fat.

Our results also show that upper airway fat content (at least up to ~20% in the tongue) did not impact inspiratory tongue movement in awake subjects.

The extent to which the protective inspiratory dilation of the tongue is maintained during sleep and how it is altered in obese people with OSA remains unclear.