Hypoglossal Stimulation Device (Inspire)

Tyler Cooper; Ahmed S. Sufyan; Salah Aboubakr.

Obstructive sleep apnea (OSA) is a common medical condition with an increasing prevalence. Repeated episodes of hypopnea or apnea can cause hypoxia, hypercapnia, and sleep fragmentation. As a result, patients with OSA can suffer from various symptoms, including snoring or gasping for air at night, excessive sleepiness, headache, irritability, difficulty concentrating, and decreased libido. Untreated OSA is associated with numerous adverse health outcomes, including increased motor vehicle accidents, hypertension, type II diabetes, strokes, atrial fibrillation, coronary artery disease, heart failure, and increased overall mortality. Hypoglossal nerve stimulation is a therapeutic option for treating OSA in patients with moderate-to-severe OSA who are resistant to or intolerant of continuous positive pressure ventilation therapy. The hypoglossal nerve stimulator detects inspiratory effort during sleep and activates upper airway musculature to prevent airway collapse. This activity reviews the anatomy and physiology, indications, contraindications, complications, and benefits of therapeutic hypoglossal nerve stimulation. Finally, this activity will highlight the role of the interprofessional team in evaluating and managing patients with OSA who receive a hypoglossal nerve stimulator.

Objectives:

• Correlate the anatomy of the upper airway and the physiology of breathing to understand the mechanisms involved in maintaining upper airway patency and the application of hypoglossal nerve stimulation.

• Identify patients with obstructive sleep apnea who may benefit from hypoglossal nerve stimulation based on their clinical indicators and the absence of absolute contraindications to the procedure.

• Apply the results of clinical trials evaluating the efficacy of hypoglossal nerve stimulation when counseling patients considering the procedure.

• Utilize effective interprofessional and interdisciplinary team processes in the outpatient clinic and hospital settings to improve outcomes for patients with obstructive sleep apnea who have undergone hypoglossal nerve stimulator placement.

Introduction

Obstructive sleep apnea (OSA) is a common medical condition with an increasing prevalence, occurring in 9% to 25% of men and 9% to 15% of women.[1][2] OSA is defined as upper airway collapse resulting in a decrease (hypopnea) or airflow loss (apnea) for at least 10 seconds.[3] Repeated episodes of hypopnea or apnea can cause hypoxia, hypercapnia, and sleep fragmentation.[4] As a result, patients can suffer from various symptoms, including snoring or gasping for air at night, excessive sleepiness, headache, irritability, difficulty concentrating, and decreased libido.[5]

Traditionally, the diagnosis of OSA relied on in-lab polysomnography. However, home sleep apnea testing is now an acceptable alternative diagnostic tool. The results from either of these tests can determine the severity of OSA using the apnea-hypopnea index (AHI) defined by the American Academy of Sleep Medicine. The severity levels are categorized as follows: Mild OSA (AHI 5-15), Moderate OSA (AHI 15-30), and Severe OSA (AHI >30).[5]

Untreated OSA is associated with numerous adverse health outcomes, including increased motor vehicle accidents, hypertension, type 2 diabetes, strokes, atrial fibrillation, coronary artery disease, heart failure, and increased overall mortality.[6][7][8]

The gold standard for treating OSA is continuous positive airway pressure (CPAP) administered via various face or nasal masks. While this treatment improves overall sleep quality and has proven effective in reducing blood pressure and the AHI, compliance is challenging for many patients, with 29% to 83% reporting <4 hours of CPAP use per night.[9][10] Compliance with treatment is especially challenging over time; noncompliance rates with long-term use range from 11% to 45%.[11][12]

Hypoglossal nerve stimulation (HGNS) is a surgical option for treating OSA. During this procedure, a stimulator is connected to the hypoglossal nerve, which controls the genioglossus muscle. When the nerve is stimulated, it triggers the contraction of the muscle, effectively preventing the collapse of the upper airway.[13] Studies have shown that HGNS significantly improves the quality of life, AHI, and oxygen desaturation index (ODI).[14]

Anatomy and Physiology

During respiration, negative inspiratory airway pressure (P_ins) exerts a pulling force on the soft tissues of the airway, moving them inward. If the P_ins is lower than the critical closing pressure (P_crit), the airway will collapse, and obstruction will occur.[15] Activation of upper airway musculature decreases P_crit and counteracts airway collapse.

However, upper airway musculature activation decreases during normal sleep, the airway narrows, and the P_crit increases.[3] Additionally, factors that contribute to airway narrowing, such as obesity and anatomical variations, can further elevate the P_crit. The P_crit will vary among populations during sleep. The P_crit can be as low as -25 cm H₂O in non-snorers, while it may be nearer to -10 cm H₂O in snorers. The P_crit is typically >0 cm H₂O in apneic patients.[15]

Among the upper airway muscles responsible for maintaining airway patency, the most crucial is the genioglossus muscle.[13] The large genioglossus muscle comprises a substantial portion of the tongue and is innervated by the hypoglossal nerve. Stimulation of the hypoglossal nerve and the subsequent contraction of the genioglossus muscle moves the tongue anteriorly, helping to maintain airway patency.[16] However, during sleep, reduced activation of the genioglossus results in the tongue falling backward into the airway, increasing the risk of airway obstruction. The risk of airway obstruction is further heightened when combined with other factors that lead to airway collapse, such as obesity.[7]

A hypoglossal nerve stimulator senses inspiratory effort via a pressure lead placed between the intercostal muscles. Changes in P_ins trigger stimulation of the hypoglossal nerve resulting in contraction of the genioglossus muscle, anterior movement of the tongue, widening of the airway, a reduction in the P_crit, and prevention of airway collapse.

Indications

Candidates for HGNS must be 18 years or older, have moderate or severe OSA by AHI standards, have failed or cannot tolerate CPAP therapy, and have no complete concentric collapse (CCC) of the soft palate.

Contraindications

The HGNS procedure is contraindicated for patients with a BMI ≥32, specific anatomic abnormalities, severe obstructive or restrictive lung disease, neurologic conditions that limit upper airway control, or have >25% central or mixed apnea on the AHI. Additionally, patients with an inability to operate the HGNS system, who are pregnant, or who plan to become pregnant are not candidates for the HGNS procedure.