Overview of Hypoglossal Stimulation Device
Obstructive sleep apnea (OSA) is a fairly common issue that impacts 9% to 25% of men and 9% to 15% of women. OSA happens when your upper airway closes up, causing either a drop in airflow (hypopnea) or complete loss of airflow (apnea) that lasts for at least 10 seconds. This issue can result in low oxygen levels in the blood (hypoxia), high carbon dioxide levels (hypercapnia), or broken sleep patterns (sleep fragmentation). You might recognize some of these symptoms – regular snoring, gasping for air while sleeping, feeling sleepy during the day, headaches, feeling irritable, problems focusing, or lowered interest in sexual activities.
OSA used to be diagnosed mainly through overnight sleep studies done at a sleep lab. Now, however, you can also do a sleep apnea test at home. The results of these tests will identify how severe the OSA is using something called the apnea-hypopnea index (AHI). The American Academy of Sleep Medicine divides OSA into three categories based on the AHI scores: mild OSA (AHI 5-15), moderate OSA (AHI 15-30), and severe OSA (AHI >30).
If not treated, OSA can lead to a number of health problems, such as car accidents due to sleepiness, high blood pressure, type 2 diabetes, strokes, irregular heartbeats (atrial fibrillation), blocked heart arteries (coronary artery disease), heart failure, and even increased risk of dying.
The best way to handle OSA is through continuous positive airway pressure (CPAP), which involves wearing a face or nasal mask while you sleep. This treatment can help improve your sleep quality and lower your blood pressure and AHI. However, many people find it difficult to keep using the mask regularly, with 29% to 83% of patients indicating that they use the mask less than 4 hours each night. Long-term use is particularly challenging, with 11% to 45% of people discontinuing treatment over time.
In cases where CPAP isn’t a good option, a surgical procedure referred to as hypoglossal nerve stimulation (HGNS) could be used. In this procedure, a stimulator is attached to the hypoglossal nerve, which controls a muscle in your throat (genioglossus muscle). When the nerve is activated, it causes the muscle to contract, allowing your upper airway to remain open. Studies have shown that HGNS could significantly improve your quality of life, reduce your AHI, and decrease oxygen desaturation index (ODI), which is a measure of oxygen level drops in blood.
Anatomy and Physiology of Hypoglossal Stimulation Device
When we breathe, the pressure of air inside our windpipe pulls the soft tissues of the airway, causing them to move inward. If this pressure is less than a certain value, known as the critical closing pressure (Pcrit), our airway can collapse and block the passage of air.
Our body tries to prevent this collapse by activating certain muscles in our upper airway, essentially ‘propping open’ the airway. But when we sleep, these muscles relax and the airway can narrow. Also, things like being overweight or having unusual physical traits can make the Pcrit go up, meaning the airway may close more often. This pressure can vary when sleeping, being weak enough not to close the airway in some people, stronger in people who snore and usually causing blockage in people with sleep apnea.
Among the muscles in our throat, a muscle called the genioglossus plays a crucial role. It’s a large muscle that makes up most of our tongue and is controlled by a nerve called the hypoglossal nerve. When this nerve is excited, it causes the genioglossus muscle to contract, which pulls the tongue forward and helps keep the airway open. However, while we sleep, this muscle isn’t as active, which can allow the tongue to fall back into the airway and block it. This risk is even higher in people who are overweight and others who are naturally more prone to airway collapse.
Healthcare providers use a device called a hypoglossal nerve stimulator to detect when we’re trying to breathe in (inspiration). The device is placed between the muscles in our chest, and when it senses the pressure of a breath, it stimulates the hypoglossal nerve. This causes the genioglossus muscle to act, moving the tongue forward, widening the airway, reducing the Pcrit, and most importantly, preventing the airway from collapsing.
Why do People Need Hypoglossal Stimulation Device
If someone is being considered for hypoglossal nerve stimulation (HGNS), certain qualifications must be met. Firstly, they must be at least 18 years old. They should also be experiencing moderate or severe obstructive sleep apnea (OSA). OSA is a condition that causes interruptions in breathing during sleep – so this would have been confirmed by something called the apnea-hypopnea index (AHI). This is a scoring system used to indicate the severity of sleep apnea.
Furthermore, candidates for HGNS should have tried and not been able to use or tolerate CPAP (continuous positive airway pressure) therapy. CPAP is a common treatment for sleep apnea where a machine helps the person breathe more easily during sleep. Lastly, the potential HGNS patient should not have a condition called complete concentric collapse (CCC) of the soft palate. This is when the soft upper part of the back of the mouth completely collapses, making the treatment less likely to work.
When a Person Should Avoid Hypoglossal Stimulation Device
The HGNS procedure, a type of treatment for sleep disorders, may not be suitable for everyone. This includes:
People with a Body Mass Index (BMI) of 32 or more. BMI is a measure that uses your height and weight to work out if your weight is within a healthy range.
People with certain physical irregularities or severe lung disease that affects breathing.
People with nervous system conditions that make it hard to control their upper throat muscles. These conditions may affect their breathing, especially during sleep.
People who have more than 25% of their sleep episodes with abnormal breathing patterns, a condition known as apnea. This term refers to episodes where breathing pauses or becomes very shallow during sleep.
It is also not suitable if you can’t operate the HGNS system on your own, or if you are currently pregnant or plan to become pregnant in the future.
Equipment used for Hypoglossal Stimulation Device
The equipment typically used in a HGNS procedure, a surgery that helps to manage sleep apnea, involves the following tools:
* A head and neck surgical set: This is a pack of tools designed specifically for surgeries in the head and neck area.
* Microdissectors: These are small, precise instruments utilized to separate and remove tissues during surgery.
* Nerve stimulator: This device sends small electric impulses to nerves to measure their function, enabling surgeons to avoid nerve damage during procedure.
* Bipolar stimulation electrodes: These are special tools used to pass a small amount of electrical current in a controlled manner. This helps to identify key nerves and ensure they are not damaged.
* MDT tunneler and MDT catheter passer: These tools are utilized to guide and place thin tubes called catheters in the body during surgery.
* Operating microscope: A high-resolution microscope that allows surgeons to view small, detailed areas during the procedure.
* Surgical loupes: These are essentially magnifying glasses, which make it easier for the surgeon to see small details clearly during the operation.
Who is needed to perform Hypoglossal Stimulation Device?
The team that will look after you during your surgery usually includes several key members.
A surgeon will be leading the procedure. Surgeons are doctors who specialize in operations. They have a lot of training and experience in performing different types of surgeries to help patients get better.
There will also be a surgical first assistant. This person assists the surgeon during the operation. They can do a range of things like preparing the surgical instruments and helping to control bleeding. Their job is to support the surgeon and make sure the surgery goes smoothly.
Anesthetists are another critical part of the team. These are special doctors who administer anesthesia, which is medicine that helps you sleep and feel no pain during the surgery. They monitor you throughout the procedure to make sure you are safe and comfortable.
A circulator or operating room nurse will also be present. These nurses help to coordinate the operating room and make sure everything runs smoothly. They also provide additional support during the surgery as needed.
And last, but not least, there will be a surgical technologist or operating room nurse. They play a vital role in sterilizing the equipment, preparing the operating room, and providing instruments to the surgeon and assistant during the operation.
All these different members make up a surgical team, each with crucial roles in ensuring your surgery goes well. They work together to give you the best possible care throughout the procedure.
Preparing for Hypoglossal Stimulation Device
Before having surgery involving Hypoglossal Nerve Stimulation (HGNS), which is a treatment for sleep disorders, all patients must be evaluated by a professional who specializes in sleep medicine or an Ear, Nose, and Throat (ENT) doctor. This is to make sure that all of the requirements for HGNS are met and there are no conditions that could make the procedure harmful. There’s a specific test called a drug-induced sleep endoscopy (DISE) which is performed to check if there is a specific condition known as complete concentric collapse (CCC) of the soft palate. This condition is important because its presence can lead to poorer results from the procedure. If CCC is not found, the HGNS procedure can go ahead.
Before the procedure, it’s important to have a clear and detailed discussion with your doctor about what the procedure involves and what the potential risks and benefits are. This is called informed consent. Your doctor should also discuss the typical schedule of follow-up appointments. It’s common to have an appointment with the ENT doctor a week after the procedure, and then a visit with the sleep medicine professional four weeks after the procedure. At this later appointment, the stimulator, which is a device implanted during the HGNS surgery, is typically activated. After the HGNS procedure, a test called titration polysomnography, which measures brain, muscle, and heart activity during sleep, is usually conducted between 12 to 16 weeks after the procedure. For long-term care, one or two sleep medicine appointments per year are normally required.
How is Hypoglossal Stimulation Device performed
The process of fitting a hypoglossal nerve stimulator is generally done in an outpatient surgery center, usually taking between 2 to 3 hours to complete. The stimulator is usually installed on the right side of the patient’s body. The process involves three separate stages, each corresponding to an individual cut made during the procedure.
The first cut is created to place the stimulator lead. This cut is made roughly 2 cm below the lower jawline and to the front of the salivary gland under the jaw. The surgeon will then find and carefully isolate the hypoglossal nerve, which controls tongue movements. They’ll use a device that sends out small electric shocks to find the nerve branches that steer the tongue muscles, particularly the muscle that pushes the tongue forward (the genioglossus muscle). Critical to the success of this procedure is that the stimulator cuff needs to be connected to the correct nerve branches. If it’s connected to the wrong branches, the ones that control the muscles pulling the tongue backward, the procedure won’t work. Once the surgeon locates the right nerve branches using the stimulator or a procedure called electromyography, they then attach the stimulator cuff and secure it using a stitch.
The second incision is done to put the neuro-stimulation generator into place. This is about 3 cm beneath the collarbone. The surgeon creates a pocket to accommodate this generator and then stitches it to a layer of tissue that covers the chest muscles (pectoralis fascia).
The third cut is made on the lower side of the chest wall to fit the pressure sensor lead. The surgeon identifies a muscle (internal intercostal muscle) through tissue dissection, separates the external and internal intercostal muscles, and places the pressure sensor between them. Using a tunneling catheter, they then link the stimulator lead and sensor lead to the neuro-stimulation generator. Before finishing the procedure, the surgeon tests the device to make sure it can make the tongue protrude properly and monitor the patient’s breathing effectively. All the cuts are then sealed and dressed using common methods. In general, patients are allowed to go home the same day.
Although some research has explored installing the stimulator and pressure sensor through a single cut, the standard approach that involves three separate incisions remains the most commonly adopted method.
Possible Complications of Hypoglossal Stimulation Device
The STAR trial, a study on a therapy to reduce sleep apnea, reported that only 2% of patients experienced severe complications after the treatment device was placed. These complications required adjustments or securing of the device. Other serious effects like blood pooling at the site (hematoma) and a collapsed lung (pneumothorax) were rare, but did happen in a few cases.
There were also some minor problems that patients reported after the procedure. Around 26% of people had discomfort related to the cut made during surgery, and 25% had discomfort not related to the incision. Other effects included a temporarily weak tongue (18%), intubation effects (12%), headaches (6%), other symptoms (11%), and minor infections (1%). But the good news is that these problems ended up going away over time. A follow-up study five years later showed that these complications decreased significantly, with only a few people reporting discomfort annually.
When it came to problems related to the treatment device itself, 40% of patients reported discomfort from the device’s electrical jolts and 21% reported abrasion or scraping of the tongue. Other complications included a dry mouth (10%), mechanical pain due to the device (6%), temporary issues with how the device worked (10%), difficulties with using the external parts of the device (6%), other symptoms (15%), and mild or moderate infections (1%). Similar to procedure-related complications, these issues also became less common over time. In the fifth year after the device was placed, only five people reported discomfort from electrical stimulation, compared to 81 in the first year.
Another study, the ADHERE Registry, showed that the most common problem with HGNS, a sleep apnea treatment, was discomfort from the stimulating device. However, this problem was less frequent 12 months after the procedure, likely because doctors made adjustments to the device’s stimulation levels.
What Else Should I Know About Hypoglossal Stimulation Device?
The STAR trial was a study involving 126 patients who were experiencing obstructive sleep apnea (OSA). Obstructive sleep apnea is a condition where breathing repeatedly stops and starts during sleep. The severity of this condition was measured by different scales such as the Apnea-Hypopnea Index (AHI), which counts the number of times per hour that your breathing stops or becomes very shallow, and the Oxygen Desaturation Index (ODI), which shows how many times per hour the oxygen in your blood drops by a certain amount due to disrupted breathing. The STAR trial also monitored patients’ levels of sleepiness and how their sleep was affecting their daily lives.
After 12 months, the study found that the breathing disruptions decreased significantly and patients reported less sleepiness and better quality of life. Furthermore, an interesting part of the analysis was when some patients were asked to stop their treatment for a week. Those who didn’t continue with the treatment saw their symptoms get worse again, while those who kept up with treatment maintained their improvement.
The researchers found similar promising results in a separate five-year follow-up study. However, they also noted a small rate of serious side effects, with some patients needing adjustments to their treatment devices.
Another registry study named the ADHERE registry confirmed this success, as it also observed significant improvements in obstructive sleep apnea symptoms and patient satisfaction levels over a 6 to 12-month period.
Overall, these studies highlight the substantial improvements in OSA symptoms and the low rate of serious side effects. Importantly, they also indicate that this type of treatment is well received by patients who have not found relief with other methods such as CPAP (Continuous Positive Airway Pressure) therapy, which is a common treatment for OSA that involves a machine that sends a constant flow of airway pressure to your throat to ensure that your airway stays open while you sleep.
