Neurophysiological monitoring of tongue muscle activation during hypoglossal nerve stimulation

Exploring hypoglossal nerve stimulation therapy for obstructive sleep apnea: A comprehensive review of clinical and physiological upper airway outcomes

Obstructive sleep apnea (OSA) is a chronic disorder characterized by recurrent episodes of upper airway collapse during sleep, which can lead to serious health issues like cardiovascular disease and neurocognitive impairments. While positive airway pressure serves as the standard treatment, intolerance in some individuals necessitates exploration of alternative therapies. Hypoglossal nerve stimulation (HGNS) promises to mitigate OSA morbidity by stimulating the tongue muscles to maintain airway patency. However, its effectiveness varies, prompting research for optimization. This review summarizes the effects of HGNS on upper airway obstruction from human and animal studies. It examines physiological responses including critical closing pressure, maximal airflow, nasal and upper airway resistance, compliance, stiffness, and geometry. Interactions among these parameters and discrepant findings in animal and human studies are explored. Additionally, the review summarizes the impact of HGNS on established OSA metrics, such as the apnea-hypopnea index, oxygen desaturation index, and sleep arousals. Various therapeutic modalities, including selective unilateral or bilateral HGNS, targeted unilateral HGNS, and whole unilateral or bilateral HGNS, are discussed. This review consolidates our understanding of HGNS mechanisms, fostering exploration of under-investigated outcomes and approaches to drive advancements in HGNS therapy.

Obstructive sleep apnea improves with non-invasive hypoglossal nerve stimulation using temporal interference

BACKGROUND

Peripheral nerve stimulation is used in both clinical and fundamental research for therapy and exploration. At present, non-invasive peripheral nerve stimulation still lacks the penetration depth to reach deep nerve targets and the stimulation focality to offer selectivity. It is therefore rarely employed as the primary selected nerve stimulation method. We have previously demonstrated that a new stimulation technique, temporal interference stimulation, can overcome depth and focality issues.

METHODS

Here, we implement a novel form of temporal interference, bilateral temporal interference stimulation, for bilateral hypoglossal nerve stimulation in rodents and humans. Pairs of electrodes are placed alongside both hypoglossal nerves to stimulate them synchronously and thus decrease the stimulation amplitude required to activate hypoglossal-nerve-controlled tongue movement.

RESULTS

Comparing bilateral temporal interference stimulation with unilateral temporal interference stimulation, we show that it can elicit the same behavioral and electrophysiological responses at a reduced stimulation amplitude. Traditional transcutaneous stimulation evokes no response with equivalent amplitudes of stimulation.

CONCLUSIONS

During first-in-man studies, temporal interference stimulation was found to be well-tolerated, and to clinically reduce apnea-hypopnea events in a subgroup of female patients with obstructive sleep apnea. These results suggest a high clinical potential for the use of temporal interference in the treatment of obstructive sleep apnea and other diseases as a safe, effective, and patient-friendly approach.

TRIAL REGISTRATION

The protocol was conducted with the agreement of the International Conference on Harmonisation Good Clinical Practice (ICH GCP), applicable United States Code of Federal Regulations (CFR) and followed the approved BRANY IRB File # 22-02-636-1279.

Beyond CPAP: modifying upper airway output for the treatment of OSA

Obstructive Sleep Apnea (OSA) is exceedingly common but often under-treated. Continuous positive airway pressure (CPAP) has long been considered the gold standard of OSA therapy. Limitations to CPAP therapy include adherence and availability. The 2021 global CPAP shortage highlighted the need to tailor patient treatments beyond CPAP alone. Common CPAP alternative approaches include positional therapy, mandibular advancement devices, and upper airway surgery. Upper airway training consists of a variety of therapies, including exercise regimens, external neuromuscular electrical stimulation, and woodwind instruments. More invasive approaches include hypoglossal nerve stimulation devices. This review will focus on the approaches for modifying upper airway muscle behavior as a therapeutic modality in OSA.

Hypoglossal nerve stimulation in adolescents with down syndrome and obstructive sleep apnea: A systematic review and meta-analysis

Objective

To evaluate the efficacy and adverse effects of hypoglossal nerve stimulation in adolescents with down syndrome and obstructive sleep apnea.

Methods

A systematic search was conducted using PubMed, Web of Science, Embase, and Scopus databases. The systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A comprehensive search strategy used a combination of Medical Subject Headings and free words with “OR” and “AND.” Articles were screened to extract data reporting apnea-hypopnea index, quality of life, voltage, follow-up duration, and complications. All included participants were adolescents with down syndrome and obstructive sleep apnea.

Results

A total of 92 articles were identified, of which 9 articles met the inclusion criteria. A total of 106 patients were included. All the studies showed that patients receiving hypoglossal nerve stimulation experienced a significant decrease in apnea-hypopnea index (at least 50%). The pooled AHI was significantly lower in patients following treatment (mean AHI reduction 17.43 events/h, 95% confidence interval 13.98–20.88 events/h, P < 0.001) after 2 case reports were excluded. The pooled OSA-18 were significantly decreased in 88 patients after treatment (mean OSA-18 reduction 1.67, 95% confidence interval 1.27–2.08, P < 0.001) after excluding 5 studies. Four investigations examined the necessity to optimize stimulation voltage for arousal during treatment. The most common complication was pain or discomfort in the tongue or mouth. Most studies had relatively short patient follow-up periods, with the most extended follow-up being 44–58 months.

Conclusion

Hypoglossal nerve stimulation significantly reduces apnea-hypopnea index and improves the quality of life; and thus, could be a potential alternative therapy for obstructive sleep apnea in adolescents with down syndrome. The adolescent's age, potential complications, adverse events, long-term efficacy, and comfort, needs to be considered while performing hypoglossal nerve stimulation.

Neurophysiological profiles of responders and non-responders to hypoglossal nerve stimulation: a single institution study

STUDY OBJECTIVES

Hypoglossal nerve stimulation (HGNS) is an effective alternative treatment for obstructive sleep apnea (OSA) that acts by opening the airway via selective stimulation of nerve fibers that innervate tongue muscles that protrude (genioglossus) and stiffen the tongue (transverse and vertical) while avoiding nerve fibers that innervate tongue muscles that retract the tongue (styloglossus and hyoglossus). There remains a subset of post-operative patients who fail to adequately respond to HGNS, in some cases due to simultaneous mixed activation of muscles that protrude and retract the tongue. This study aims to characterize the relationship between neurophysiological data from individual tongue muscle activation during intraoperative electromyographic (EMG) recordings and post-operative AHI responses to HGNS..

METHODS

A single institution review of 46 patients undergoing unilateral HGNS implantation for OSA. Patients were separated into responders and non-responders through comparison of pre and postoperative AHI. Neurophysiological data included EMG responses of the genioglossus, styloglossus/hyoglossus, intrinsic/vertical, and hyoglossus (neck) muscles to intraoperative stimulation using unipolar (--- and o-o) and bipolar (+-+) settings.

RESULTS

The overall treatment success rate was 61% as determined by a post-operative AHI <20 events/hr with a greater than 50% AHI reduction. We observed no statistically significant relationships between treatment response and individual muscle responses. However, we did note that increasing BMI was correlated with worse post-operative responses.

CONCLUSIONS

Although we noted a significant sub-group of clinical non-responders to HGNS post-operatively, these patients were not found to exhibit significant inclusion of tongue retractors intraoperatively on neurophysiological analysis. Further research is needed to delineate additional phenotypic factors that may contribute to HGNS treatment responses.

Non-Instrumental Test for the Evaluation of Tongue Function

The tongue undergoes various negative adaptations in the presence of local or systemic pathologies, adversely its behavior within the body context. Tongue assessments to correctly diagnose its functions are carried out using instrumentation, such as ultrasonography, magnetic resonance imaging, electromyography and different intraoral devices (swallowing, strength, posture, phonesis). Currently, there is no dynamic non-instrumental test in the scientific literature to highlight any lingual dysfunctions. The article describes a non-instrumental test for the assessment of lingual function in the body context, to obtain preliminary information on the quality of the neurological activities of the tongue, with respect to the balance and muscle strength that the patient expresses. The text briefly reviews the anatomy of the tongue and describes a clinical case to better understand how to use this test. Further studies will be needed for the validation of the test.

A Missing Voice: The Lingual Complex and Osteopathic Manual Medicine in the Context of Five Osteopathic Models

The five osteopathic models recognized by the American Association of Colleges of Osteopathic Medicine guide clinicians in the evaluation and therapeutic choice which must be the most appropriate concerning the patient's needs. Skeletal muscles represent an important interpretation, such as screening and treatment, on which these models are based. A muscle district that is not considered by the usual osteopathic practice is the tongue. The lingual complex has numerous functions, both local and systemic; it can adapt negatively in the presence of pathology, just as it can influence the body system in a non-physiological manner if it is a source of dysfunctions. This paper, the first of its kind in the panorama of scientific literature, briefly reviews the anatomy and neurophysiology of the tongue, trying to highlight the logic and the need to insert this muscle in the context of the five osteopathic models. The clinician's goal is to restore the patient's homeostasis, and we believe that this task is more concrete if the patient is approached after understanding all the contractile districts, including the tongue.

Intraoperative identification of mixed activation profiles during hypoglossal nerve stimulation

STUDY OBJECTIVES

The effectiveness of hypoglossal nerve stimulation (HGNS) in the treatment of obstructive sleep apnea (OSA) depends on the selective stimulation of nerve fibers that innervate the tongue muscles that produce tongue protrusion (genioglossus) and stiffening (transverse/vertical) while avoiding fibers that innervate muscles that produce tongue retraction (styloglossus/hyoglossus). Postoperative treatment failures can be related to mixed activation of retractor and protrusor muscles, despite intraoperative efforts to identify and avoid nerve fibers that innervate the retractor muscles. This study describes a novel intraoperative protocol that more optimally identifies mixed activation by utilizing an expanded set of stimulation/recording parameters.

METHODS

This study was a case series in a university hospital setting of patients undergoing unilateral hypoglossal nerve stimulation implantation for obstructive sleep apnea. Data included electromyographic responses in the genioglossus and styloglossus/hyoglossus to intraoperative stimulation with an implantable pulse generator using unipolar (- - -, o-o) and bipolar (+-+) settings.

RESULTS

In a subset of patients (3/55), low-intensity unipolar implantable pulse generator stimulation revealed significant mixed activation of the styloglossus/hyoglossus and genioglossus muscles that was not evident under standard bipolar implantable pulse generator stimulation conditions. Additional surgical dissection and repositioning of the electrode stimulation cuff reduced mixed activation.

CONCLUSIONS

A novel intraoperative neurophysiological monitoring protocol was able to detect significant mixed activation during hypoglossal nerve stimulation that was otherwise absent using standard parameters. This enabled successful electrode cuff repositioning and a dramatic reduction of mixed activation.