Obstructive Sleep Apnea (OSA) is a sleep disorder characterized by the repeated collapse of the upper airway during sleep, leading to fragmented rest and lowered oxygen levels. Continuous Positive Airway Pressure (CPAP) therapy is the standard treatment, using air pressure to keep the throat open. However, many patients struggle with consistent use due to mask discomfort or machine noise, resulting in poor adherence. This challenge has driven the development of alternative solutions for those who cannot tolerate traditional therapy. One innovation is an internal, surgically placed device that manages airway obstruction from within the body.
Hypoglossal Nerve Stimulation: Defining the Technology
The system often called an “implanted CPAP” is technically a Hypoglossal Nerve Stimulation (HNS) system. HNS actively stabilizes the airway rather than providing passive air pressure. This technology uses three implanted components to monitor and control the tongue muscles. The pulse generator, a small, pacemaker-like device, is placed beneath the skin in the upper chest or below the collarbone.
The generator is connected to a sensing lead, which is placed between the ribs to monitor the patient’s breathing movements. When the patient inhales, the sensing lead detects the effort and signals the pulse generator. The third component is the stimulation lead, which is cuffed around a branch of the hypoglossal nerve that controls tongue movement.
In response to the signal, the generator delivers a mild electrical impulse through the stimulation lead to the hypoglossal nerve. This impulse causes the main tongue muscle, the genioglossus, to stiffen and move forward. This action keeps the tongue from collapsing back into the throat, preventing the apneas characteristic of OSA. The process is synchronized with the breathing cycle, working only when needed to maintain airway patency.
Determining Patient Eligibility
HNS therapy is reserved for patients who cannot successfully use or tolerate CPAP therapy. Candidates must have a confirmed diagnosis of moderate to severe OSA, typically defined by an Apnea-Hypopnea Index (AHI) between 15 and 65 events per hour. The patient’s body mass index (BMI) is also a factor; most candidates must have a BMI at or below $35 \text{ kg/m}^2$.
The specific pattern of airway collapse must be evaluated using a Drug-Induced Sleep Endoscopy (DISE). This procedure involves sedating the patient to visually examine the throat with a camera. Eligibility requires the DISE to confirm that the obstruction is not caused by a complete, concentric collapse of the soft palate, as the device is less effective in these cases. Additionally, a high percentage of central sleep apnea events (typically less than 25% of the total AHI) is an exclusion criterion, since HNS treats only obstructive sleep apnea.
The Implantation Procedure and Immediate Recovery
The implantation of the HNS system is a minimally invasive surgical procedure, typically performed on an outpatient basis under general anesthesia, lasting two to three hours. The surgeon makes small incisions in three locations to place the device components. One incision is made in the upper chest for the pulse generator, and a second is used to place the breathing sensor lead near the ribs.
A third incision is made under the chin to access and place the cuff electrode around the branch of the hypoglossal nerve. Patients usually return home the same day and manage initial discomfort and swelling with prescribed oral pain medication. Most individuals can resume light daily activities within a few days to a week following the operation.
The therapy is not immediately activated after the procedure; a healing period is required for the tissues to recover. This phase typically lasts about four weeks, allowing the incision sites to close and the internal components to settle. After this period, the patient returns to the clinic for device activation and initial programming.
Long-Term Management and Measured Effectiveness
Once activated, patients control their therapy using a handheld remote, turning the system on before sleep and off upon waking. The implanted pulse generator contains a battery that typically lasts between eight and twelve years, depending on stimulation settings and frequency of use. Replacing the device requires a minor outpatient procedure to exchange the pulse generator, but the leads usually remain in place.
Objective data confirms the effectiveness of HNS therapy for selected patients. Clinical trials show a significant reduction in OSA severity, with AHI scores decreasing by 68% to 75% after one year of use. This often translates to a reduction of about 18 events per hour, moving patients out of the severe OSA category. Patients also report a decrease in daytime sleepiness, as measured by the Epworth Sleepiness Scale.
Adherence rates for HNS are consistently high, often exceeding 90%, which is a significant advantage over CPAP for non-adherent patients. To ensure optimal long-term results, a follow-up titration study is usually performed two to three months after activation. During this study, a sleep technician fine-tunes the stimulation settings to optimize the airway opening while the patient sleeps.