May 072014

Image: Inspire Med Systems
Hypoglossal Nerve Stimulation for Sleep Apnea Wins FDA Approval

The U.S. Food and Drug Administration approved Inspire Medical Systems' pacemaker-like hypoglossal nerve stimulator for patients with moderate to severe obstructive sleep apnea (OSA) who cannot tolerate continuous positive airway pressure (CPAP). The Inspire device stimulates key airway muscles controlled by the hypoglossal nerve, and the maintained muscle tone prevents airway occlusion and apneic events during sleep. As PulmCCM reported earlier this year, the STAR trial demonstrated the Inspire device could cut apnea events and hypoxemia by almost 70% after one year of use, in highly selected patients with OSA.

The surgically-implanted device includes a small generator in the upper chest like a defibrillator or pacemaker (Inspire is a spinoff from device behemoth Medtronic). An electrical stimulator lead is tunneled from the generator to the back of the throat. Sensors detect when the patient is making inspiratory efforts, and stimulate the hypoglossal nerve in synchronized fashion. Patients activate the device upon going to sleep, with a hand-held remote, and turn it off upon waking.

About 15 million people in the U.S are believed to have sleep apnea. CPAP is the most effective and well established treatment, but only about half of patients prescribed CPAP actually use it. Common complaints are poor-fitting masks, claustrophobia, oral or nasal secretions that build up in the mask, or pulling the mask off while asleep. The FDA's advisory panel voted 12-0 in February to recommend approving the device, based almost totally on the STAR trial.

Will Hypoglossal Nerve Stimulation Work in the Obese with OSA?

The news media stimulated its own buzz, reporting Americans have a "new option" for treating OSA -- but almost all news reports failed to mention that the STAR trial demonstrated Inspire's benefit mainly in a relatively atypical population: people with sleep apnea who are not obese.  The mean body mass index of enrolled patients was 28, and those with BMI > 32 were excluded. Obesity is the most common cause and comorbidity in people with obstructive sleep apnea, and correlates with severity of OSA. Patients also had to undergo endoscopy during drug-induced sleep to verify they did not have complete concentric collapse of their airway with sleep (which the device cannot easily remedy; it was present in ~30% of endoscoped patients). Patients with an apnea-hypopnea index > 50 were also excluded. Investigators had to recruit 1,050 patients to enroll 126 meeting the criteria.

Why so selective? As the authors of the original paper put it, "The feasibility studies conducted by our team identified a BMI of 32 or lower or an AHI score of 50 events per hour or less as phenotypic risk factors that favorably affect the success of upper-airway stimulation."

In other words, investigators knew they were more likely to demonstrate a benefit in less-overweight or obese patients. That's certainly an appropriate way to design a clinical trial. But it's also an acknowledgement that they knew the therapy would probably not work as well, or possibly at all, in more obese patients who might carry much of the burden of OSA in the U.S. Yet no statement like "These results may not apply to more obese patients" or "These results should be replicated in a larger population more representative of the total population with obstructive sleep apnea before widespread adoption of this therapy is considered" appears in the discussion, nor in 5 news reports I read.

Innocent oversight, or advantageous omission?

The Inspire device is expected to be commercially available later in 2014. Inspire's chief executive told reporters the device will cost $30,000 including the cost of surgery. Adverse effects were few and included local discomfort, tongue weakness and having one more remote to keep track of.

Read more: STAR trial demonstrates benefit of hypoglossal nerve stimulation for obstructive sleep apnea

How hypoglossal nerve stimulation works (from Inspire's website):


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