TeachableMedicalNews article 11272019
Teachable moment in classrooms:
- respiratory system chapter – anatomy of upper airways
- nervous system chapter – organs innervated by cranial nerve XII (hypoglossal)
- skeletal muscle chapter – electric excitation of skeletal muscles lead to contraction (excitation-contraction coupling)
The news item: Recently, several articles appeared about an electrical device called Inspire:
Sleep apnea patient finds rest with implant device: “It saved my life”
An estimated 22 million Americans suffer from sleep apnea, putting them at greater risk for diabetes, heart disease, stroke and memory loss
The articles mention that the device treats sleep apnea, and that the device sends electrical impulses to the throat muscles.
So, Why Do I Care?? Sleep apnea, or more precisely, obstructive sleep apnea, is a sleep disorder that affects about 22 million people in the US. Those people are not just losing sleep, but are at higher risk for several cardiovascular diseases, and for daytime sleepiness. While not every patient is a good candidate for the Inspire device, the patients with the device show significant improvement in sleep quality and time.
Plain English, Please!!! So, let’s talk about sleep apnea first. Apnea is a brief closure of the airways where the closure stops air from getting into the lungs. The lower portion of our airways have solid cartilage framework (trachea, bronchi), so narrowing rarely occurs; it is always open, like a steel pipe. However, in the upper airways (mouth, soft palate) we have muscles that surround those airways, and the inappropriate relaxation of the muscles can lead to closure of the upper airway; imagine putting on a sock: it’s easy when we open it up with our fingers, but it’s harder to put our toes through it when the sock is collapsed on the floor.
Second, let’s talk about throat muscles. While we do have muscles in the throat (anatomically called pharynx), in the soft palate, and in the tongue, surprisingly, the muscles in the tongue are the culprit in narrowing of the airways during sleep. The task of the Inspire device is to contract the muscles inside our tongue.
Third, let’s talk about muscle contraction. How come those muscles of the upper airways stop working when we’re asleep? That happens, because muscles need an instruction, a nerve signal, to work, to contract. When we’re asleep, our brain is no longer sending nerve signals to the tongue muscles, so the muscles relax, and may obstruct the upper airways. It follows then that during our sleep we could reopen the closed airways by sending a signal to the muscles of the tongue. Because most of the tongue muscles get their nerve signal through a nerve called cranial nerve XII, it makes sense that the wire of the Inspire device sends electrical impulses to cranial nerve XII. In turn, those nerve impulses will make the tongue muscles to contract, and keep the airways open.
