This article previously ran in the Q1 2023 issue of A2Zzz.
An estimated 23 million people in the United States have obstructive sleep apnea (OSA) and an estimated 82% of people with OSA are undiagnosed.1 Some factors that may contribute to a lack of diagnosis are financial issues (e.g., a person’s insurance may be unwilling to pay for a sleep study), physical difficulties (e.g., quadriplegia, mental or communication problems) and lack of access to a sleep center (e.g., the person lives in a rural setting or has transportation issues). To counteract these problems, the development of a device that would allow people to undergo a sleep study in their homes (i.e., home sleep testing [HST]) and allow more people to be diagnosed and treated more cost effectively would be ideal. To this end, various HST devices have been developed as an alternative for screening people for OSA. Much research has focused on the use and efficacy of HST devices as a screening tool for OSA.2,3 However, in recent years, scientists have begun investigating the use of HST for the longterm follow-up of patients treated with non-continuous positive airway pressure (non-CPAP) therapy for OSA — in particular, hypoglossal nerve stimulation.
In OSA, upper airway muscles relax excessively during sleep, which allows structures supported by them to collapse into and block (i.e., obstruct) the upper airway. This restricts airflow and decreases the amount of oxygen in the blood. To compensate for the reduced oxygenation, a person makes increasingly strong efforts to breathe. When the oxygen level falls to a certain point, the respiratory center in the brain triggers a brief arousal (lasting for a few seconds) during which the upper airway muscle tone is restored and the person is able to take some deep, quick breaths. Once the blood oxygen level is restored, the person resumes sleep, which sets the stage for another apnea event.
A physician who suspects a patient has OSA may refer the person to a sleep center for a polysomnographic (PSG) study. In a PSG study, sensors are applied to record a patient’s brainwaves, nasal and oral airflow, thoracic effort, heart rhythm, leg movements and blood oxygen saturation. If the diagnostic study reveals sleep apnea, the person may then undergo another PSG study, which involves a trial of continuous or bilevel positive airway pressure (CPAP or BPAP, respectively) treatment in which pressurized air is applied to the upper airway through a facial or orofacial mask to prevent upper airway collapse. During the CPAP/BPAP treatment PSG study, the pressure is slowly increased (i.e., titrated) to the level that prevents apnea events.
After the titration study, a person comes to a sleep center at regular intervals for a retitration study to determine whether the pressure is effectively preventing apnea episodes or whether the pressure needs adjusting. For many patients, subsequent visits to a sleep center can be problematic because this requires taking days off of work or school, sleeping in a strange bed and environment, and experiencing discomfort because of the sensors.
In addition, some patients are not compliant with positive airway pressure (PAP) treatment because of discomfort with the pressure or mask or feeling constricted (e.g., unable to sleep on stomach) or claustrophobic when wearing the mask. In this situation, a patient may seek non-PAP therapy. One such therapy is hypoglossal nerve stimulation. In this therapy, the hypoglossal nerve (i.e., cranial nerve XII) is stimulated during an OSA episode. The stimulation flattens and protrudes the tongue forward thereby opening the airway and preventing OSA.
Early animal studies4-6 revealed that stimulation of the hypoglossal nerve could protrude the tongue and that long-term stimulation did not damage the nerve. These findings gave scientists the hope of using hypoglossal nerve stimulation to treat OSA.
In 2001, Schwartz and colleagues7 were the first team to report successfully using hypoglossal nerve stimulation to prevent OSA in humans. Until this point, scientists knew that hypoglossal nerve stimulation could briefly relieve upper airway collapsibility but whether this action could be used to treat OSA was unknown.4-6 In their study, Schwartz implanted patients with OSA with a novel device (Inspire I Stimulating System; Medtronic Inc, Minneapolis, Minnesota). The device consisted of an intrathoracic pressure sensor (to sense when an apnea was occurring, based on thoracic movements), a programmable pulse-generating system (to apply a pulse on inspirations during an apnea event) and a stimulating electrode (to relay the signal from the pulse generator to the hypoglossal nerve). The patient’s hypoglossal nerve was stimulated. Patients used a remote device to turn on the hypoglossal nerve stimulator at bedtime to initiate treatment and to turn it off in the morning.
Schwartz assessed the patients’ sleep and breathing patterns pre- and postimplantation at one month, three months, six months and 11 months. They found that unilateral hypoglossal nerve stimulation reduced the apnea-hypopnea index by 58%, rapid eye movement (REM) sleep by 65% (with a trend toward greater amount of the deeper stages of non-REM sleep) and the severity of desaturations. All patients tolerated long-term nocturnal stimulation, and none experienced adverse effects from the nerve stimulation (e.g., tongue deviation, atrophy or hypertrophy; pain; numbness; inflammation; or alterations in speech and swallowing).
In 2004, Penzel et al.8 described a novel ambulatory monitoring system, which combined peripheral artery tomography (PAT), oximetry and wrist actigraphy (i.e., WatchPAT) to noninvasively detect sleep apnea and arousals. PAT is used to measure arterial pulse volume changes in the finger. Extending from the watch-like component was a wire that connected to a finger sensor that detected oxygen saturation and another wire that connected to a finger sensor that detected vascular tone, which is influenced by blood pressure, peripheral vascular resistance, blood volume in the finger and activation of the autonomic nervous system (which regulates involuntary physiologic processes such as heart rate, blood pressure and respiration). (In later versions of the WatchPAT, one finger probe is used that records blood oxygen saturation and PAT data. The WatchPAT data are ultimately transmitted to a webserver and can be downloaded by a physician for review.)
In their study, patients with suspected OSA were recorded simultaneously via PSG and WatchPAT. The WatchPAT device reliably detected apneas and hypopneas and it was very sensitive in detecting arousals. Penzel concluded that continuous monitoring of autonomous nervous functions during sleep could be used for diagnostic purposes.
The findings of later WatchPAT studies supported their findings. For example, Choi et al.3 demonstrated good agreement and a high (94%) correlation in the apneahypopnea index (AHI) and lowest oxygen saturation, and a significantly high concordance in the severity of AHI between PSG and WatchPAT. Zhang and colleagues9 similarly found a significant (93%) correlation in the AHI between the two methods; WatchPAT diagnosing rate was 93% with a sensitivity of 94.7% (i.e., true-positive result) and a specificity of 80.0% (true-negative result). Zhang noted that, at lower AHI levels, WatchPAT tended to overestimate disease severity and, at higher AHI levels, it tended to underestimate disease severity; nevertheless, they suggested it was a reliable ambulatory method for detecting OSA.
As a diagnostic tool, HST seems to be effective. However, whether the same is true for patients undergoing follow-up studies after OSA treatment such as hypoglossal nerve stimulation is not fully clear and has recently begun to be investigated. Some findings have been encouraging. Steffan and colleagues10 investigated whether using HST for the initial OSA evaluation and then follow-up HST studies at five months, 12 months and 24 months would be similar to the results obtained when using follow-up PSG studies at the six-, 12- and 24-month evaluations in patients implanted with a hypoglossal nerve stimulator. They compared two groups of patients: those who were followed with HST after implantation and those who were followed with PSG after implantation. They found no significant differences between the two groups at two months and beyond. The subjective and objective treatment outcomes and compliance were comparable, whether in the shortterm follow-up (i.e., six months) or in long-term follow-up (i.e., one year and two years).
With the advent of increasing use of HST devices, the American Academy of Sleep Medicine11 has made the following recommendations regarding HST:
- PSG or home sleep apnea testing with a technically adequate device can be used for the diagnosis of OSA in uncomplicated adult patients presenting with signs and symptoms that indicate an increased risk of moderate to severe OSA.
- If a single home sleep apnea test (HSAT) is negative, inconclusive or technically inadequate, then a PSG study should be performed to determine a diagnosis of OSA.
- Clinical tools, questionnaires and prediction algorithms should not be used to diagnose OSA in adults without PSG or HST.
- PSG rather than HSAT should be used for the diagnosis of OSA in patients with significant complications such as cardiorespiratory disease, potential respiratory muscle weakness due to neuromuscular condition, awake hypoventilation or suspicion of sleep-related hypoventilation, chronic opioid medication use, history of stroke or severe insomnia.
HST has several advantages, including the ability to be performed in the comfort of a patient's home environment and it is less expensive than traditional PSG. However, HST has limits. While it is more effective as a screening test for OSA but not for other sleep disorders such as periodic leg movement disorder (PLMD) and it is not currently recommended for all patients (e.g., patients with central and mixed apneas, patients who are unable to operate the remote, patients with implantable devices that may interfere with the HST device or vice versa). For now, research continues to determine how to best utilize HST to make sleep testing more available to patients and more effective for follow-up.
- American Sleep Apnea Association (ASAA). Sleep apnea information for clinicians. ASAA: Washington, DC. Accessed on Jan 16, 2023. https://www.sleephealth.org/asaa/sleep-apnea-information-for-clinicians/#:~:text=A%20very%20short%20course%20on%20sleep%20
- Kirsch DB. Pro: Sliding into home: Portable sleep testing is effective for diagnosis of obstructive sleep apnea. Journal of Clinical Sleep Medicine. 2013;9:5-7.
- Choi JH, Kim EJ, Kim YS, et al. Validation study of portable device for the diagnosis of obstructive sleep apnea according to the new aasm scoring criteria: Watch-pat 100. Acta Otolaryngologica. 2010;130:838-843. doi:10.3109/00016480903431139
- Eisele DW, Schwartz AR, Hari A, et al. The effects of selective nerve stimulation on upper airway airflow mechanics. Archives of Otolaryngology — Head and Neck Surgery. 1995;121:1361-1364. doi:10.1001/archotol.1995.01890120021004
- Hida W, Kurosawa H, Okabe S, et al. Hypoglossal nerve stimulation affects the pressure-volume behavior of the upper airway. American Journal of Respiratory and Critical Care Medicine. 1995;151(2 Pt 1):455-460. doi:10.1164/ajrccm.151.2.7842206
- Goding GJ, Eisele DW, Testerman R, et al. Relief of upper airway obstruction with hypoglossal nerve stimulation in the canine. Laryngoscope. 1998;108:162-169. doi:10.1097/00005537-199802000-00003
- Schwartz AR, Bennett ML, Smith PL, et al. Therapeutic electrical stimulation of the hypoglossal nerve in obstructive sleep apnea. Archives of Otolaryngology — Head and Neck Surgery. 2001;127:1216-1223. doi:10.1001/ archotol.127.10.1216
- Penzel T, Kesper K, Pinnow I, et al. Peripheral arterial tonometry, oximetry and actigraphy for ambulatory recording of sleep apnea. Physiol Meas. Aug 2004;25(4):1025-1036. doi:10.1088/0967-3334/25/4/019
- Zhang J, Wang CY, Wang NY, et al. Evaluation of a portable device based on peripheral arterial tone in the detection of obstructive sleep apnea. Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Zhi (Chinese Journal of Otorhinolaryngology Head and Neck Surgery). Feb 2012;47:112-116. In Chinese.
- Steffen A, Konig IR, Baptista PM, et al. Home sleep testing to direct upper airway stimulation therapy optimization for sleep apnea. Laryngoscope. Apr 2021;131(4):E1375-E1379. doi:10.1002/ lary.29043
- Kapur VK, Auckley DH, Chowdhuri S, et al. Clinical practice guideline for diagnostic testing for adult obstructive sleep apnea: An american academy of sleep medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2017;13:479-504. doi:10.5664/jcsm.6506