Obstructive sleep apnea (OSA) is a disorder where throat muscles and soft tissues relax and collapse during sleep, blocking the airway and interrupting breathing. The standard treatment for moderate to severe OSA is Continuous Positive Airway Pressure (CPAP) therapy, which uses a mask to deliver pressurized air to hold the airway open. Many individuals find the CPAP mask uncomfortable or struggle with consistent use. A non-mask alternative, often called an “Internal CPAP,” is a surgically implanted device that prevents airway collapse by stimulating muscles. This technology, known as Hypoglossal Nerve Stimulation (HNS), addresses the obstruction by providing timed muscle activation instead of air pressure.
Components of the Internal Airway Stimulation System
The internal airway stimulation system is fully implanted beneath the skin and consists of three primary hardware components that manage the airway during sleep.
The implantable pulse generator (IPG) functions similarly to a pacemaker, containing the battery and computer chip. This generator is typically placed in a small pocket under the skin in the upper chest, just below the collarbone.
The sensing lead is a thin wire positioned between the intercostal muscles in the chest wall. Its purpose is to detect subtle muscular movements associated with the beginning of the breathing cycle (inhalation). This lead provides the crucial timing signal to the pulse generator, indicating precisely when the system needs to activate.
The stimulation lead is cuffed around a specific branch of the hypoglossal nerve in the neck. The hypoglossal nerve is the 12th cranial nerve, controlling the movement of the tongue and other upper airway muscles. This lead delivers a mild electrical impulse to the nerve when signaled by the generator, causing the necessary muscle contraction to open the airway.
The Mechanism of Airway Opening
The system’s effectiveness relies on precisely synchronizing electrical stimulation with the patient’s natural breathing pattern during sleep. The process begins when the sensing lead detects the initiation of a breath, sending a signal to the implantable pulse generator. This signal acts as a trigger, ensuring the device is only active during the inhalation phase when the airway is most likely to collapse.
In immediate response to the inhalation signal, the pulse generator emits a low-level electrical impulse. This impulse travels through the stimulation lead to the targeted branches of the hypoglossal nerve. Stimulating the nerve causes the genioglossus muscle (the main muscle of the tongue) and other related muscles to contract.
The muscle contraction is carefully calibrated to move the tongue base slightly forward. This forward movement creates tension and stiffness in the upper airway, preventing the tongue and soft palate from collapsing and blocking airflow. This technology uses the body’s own musculature to actively manage the airway.
The Implantation Procedure and Activation
The process begins with a surgical procedure, typically performed on an outpatient basis under general anesthesia. The surgeon makes two small incisions: one in the neck for the stimulation lead placement, and a second in the upper chest to place the pulse generator and sensing lead. The entire procedure generally takes about two hours, and the patient can usually return home the same day.
Patients typically recover for about one week, limiting physical activity to allow incisions to heal. The device is not immediately activated; a healing period of approximately one month is required before the first activation visit. During this visit, the physician turns on the device and provides the patient with a remote control to operate the system at home.
A specialized sleep study is performed, typically three months after activation, to calibrate the system for optimal performance. This titration study monitors the patient’s sleep while the device is running, allowing the physician to fine-tune the electrical stimulation level. The goal is to identify the precise setting that eliminates airway obstructions without causing discomfort or waking the patient.
Determining Patient Eligibility
Candidacy for the internal airway stimulation system is determined by a strict set of medical criteria, as the treatment is not suitable for all patients with OSA.
A primary requirement is documented failure or intolerance to traditional Positive Airway Pressure (PAP) therapy, such as inability to use the CPAP machine consistently. Patients must also have moderate to severe OSA, generally defined by an Apnea-Hypopnea Index (AHI) score between 15 and 65 events per hour.
Body mass index (BMI) is an important factor, with most guidelines recommending a BMI of less than 32 kg/m\(^2\).
Furthermore, a specialized physical examination known as a drug-induced sleep endoscopy (DISE) is required. This procedure examines the upper airway collapse pattern while the patient is under mild sedation. The DISE ensures the obstruction is due to tongue base collapse and not a complete concentric collapse of the soft palate, which the stimulation system cannot effectively treat.