Earlier this month, the US Food and Drug Administration expanded the approved indications for the Inspire Upper Airway Stimulation system, raising the upper limit for body mass index from 32 to 40 kg/m2 and increasing the upper limit for the apnea hypopnea index to 100 events/hour. This has been met with some surprise by colleagues, given what we know about outcomes.
Are the results of Inspire Upper Airway Stimulation poorer with greater body mass index and greater apnea-hypopnea index?
In a word, yes. Multiple large research studies have shown that Upper Airway Stimulation treatment outcomes are better in those with lesser body mass index and lesser apnea-hypopnea index. A study from the University of Kansas published earlier this month in the Journal of Clinical Sleep Medicine showed that weight loss, even after implantation of the Upper Airway Stimulation system, was associated with better outcomes.
For apnea-hypopnea index, the answer may be as simple as the fact that, if your sleep apnea is worse, it is less likely that any treatment will meet the threshold for success: at least a 50% reduction in the apnea-hypopnea index AND a post-treatment level below 15 or 20 events/hour. I have never found that it made sense to limit the indications for hypoglossal nerve stimulation based on apnea-hypopnea index, as taking a patient from an apnea-hypopnea index of 90 to 25 is a pretty big improvement in their sleep apnea and a good outcome for someone who cannot tolerate positive airway pressure. I will not discuss apnea-hypopnea index further here.
Body mass index is a crude measure of body weight, but, in general, those with greater body mass index have more muscle and/or fat weight. What may be more important is the likely genetic basis for body weight distribution. Some people store more body weight – muscle and/or fat – in their head and neck, and it is likely this weight that is the key when it comes to obstructive sleep apnea. While hypoglossal nerve stimulation moves the tongue forward, greater body weight in the head and neck likely means that there is more tissue (greater volume) in the tongue and all other structures surrounding the throat. Based on findings of drug-induced sleep endoscopy, this suggests that moving the tongue forward may be less able to keep the throat open for breathing because the tongue or other structures (soft palate or the sides of the throat) may still block breathing.
Why would it make sense to expand the body mass index indications for Upper Airway Stimulation?
Patients with greater body mass index who do not tolerate positive airway pressure therapy (e.g., CPAP or BPAP) may not have other great options. In general, in patients with body mass index above 35 kg/m2 in particular, treatment outcomes are poorer for ALL alternative treatments besides positive airway pressure therapy. Many of these patients have two main options: weight loss or maxillomandibular advancement, although even this procedure has poorer outcomes in these patients than in those with lesser body mass index. Weight loss will likely become more important in obstructive sleep apnea treatment because of the GLP-1 agonists and other medications in clinical trials, but there are many patients who are not candidates for weight loss.
For patients with greater body mass index (for example, in the range of 35-40 kg/m2), hypoglossal nerve stimulation approaches (like Upper Airway Stimulation) may be a great option, specifically because they may offer outcomes that, while imperfect, may be much better than other alternatives to positive airway pressure.
What is the next step forward?
Because relatively little research has been done on those with body mass index above 32 kg/m2 – and even less on those with body mass index above 35 kg/m2, clearly we need to learn more. I have led or been involved with multiple studies evaluating how we can choose the best possible candidates for Upper Airway Stimulation or other similar technologies. These treatments are expensive but important treatment options. It is essential that we know as much as we can about how to use them wisely.
We have learned much in those with body mass index up to 32 kg/m2, but there is more to learn. This is even more striking for potential candidates with body mass index above 32 kg/m2. I look forward to learning more. I look forward to being part of the effort to do so.