Obstructive sleep apnoea is more than just an extreme form of snoring. In this disorder, the muscles in the throat and upper airway repeatedly collapse while you sleep, leading to a decrease in the amount of oxygen in your blood. This also partially rouses you from sleep many times a night and leads to poor sleep and an increased risk of accidents, hypertension, heart attack and stroke.
While there are several treatments available for obstructive sleep apnoea, we don’t truly understand how the muscles of the upper airway cause the condition.
We are currently making the first direct biomechanical measurements of the upper airway in humans. By examining how the mechanical properties of these muscles are altered in people with obstructive sleep apnoea and how the brain drives these muscles, we will be able to improve treatments.
The Bilston Group is using MRI to measure the stiffness of the upper airway muscles and how they move during normal breathing, so we can understand what predisposes them to collapse. In conjunction with the Gandevia Group, we are also measuring the electrical signals from the brain to the major muscle in the upper airway, the genioglossus, using electromyography. This will help us understand what signals the brain is sending to cause the muscle to contract with breathing to keep the upper airway open.
So far we have observed the characteristics of the tongue and the motion of the genioglossus in people with obstructive sleep apnoea compared with healthy controls. We have found that the motion is significantly different from healthy subjects, and also varies with the severity of the disease. As the disease develops, tongue motion increases, but is not well coordinated, so that instead of opening the airway, contraction can widen one region and narrow another. In the most severe cases, motion appears to reduce or cease, so that the genioglossus does not dilate the airway during each breath.
We are now in a unique position to visualise the neuro-mechanical coupling (how the brain communicates via the electrical signals with muscles) in the upper airway. This will provide critical information about how the upper airway works normally and how its function is impaired in obstructive sleep apnoea.
In the longer term we will apply this knowledge to assessment of the treatment of obstructive sleep apnoea and to explore further how the upper airway behaves in different conditions.