Sleep apnea is a common condition. As many as 26% of all Americans may suffer from this condition, in which there are long pauses between breaths during sleep. Unfortunately, many patients with sleep apnea do not tolerate the most effective current therapy, continuous positive airway pressure, or CPAP. For some of these people, a new approach pacemaker therapy may be an alternative.
Pacemakers for sleep apnea? This must be a “typo,” right? Don’t you really mean heart pacemaker? No, this isn’t a typo. Pacemakers are some of the newest treatments for sleep apnea. Before explaining how they work, a short physiology lesson is necessary.
Normally, when you breathe in, air flows from the nose and mouth, past the back of your tongue, through the trachea and down into your lungs. This occurs because nerve signals from the brain activate the diaphragm to produce inspiration. The resulting negative pressure pulls air in. However, these nerve signals also stimulate muscles surrounding the throat, including the tongue to contract in order to prevent the airway from being suctioned closed with breathing. Sleep apnea occurs when these processes fail during sleep, and consequently air does not enter the lungs.
There are two types of sleep apnea. The most common is obstructive sleep apnea, which occurs when there is repetitive collapse of airway at the back of the throat. In obstructive apnea, the stimulus to the throat muscles is insufficient to prevent their collapse and the airway becomes blocked. Less common is central sleep apnea. In central apnea, nerve signals from the brain are absent for prolonged periods of time, and there is no effort made to breathe during these intervals.
In a recent study, pacing of the hypoglossal nerve in the neck during sleep was effective treatment for people with moderate to severe obstructive sleep apnea. Twelve months after pacemaker insertion, the average number of obstructed breathing events decreased by approximately 50%. In addition, nighttime oxygen levels improved, as did measures of quality of life and daytime sleepiness. There were few side effects.
How does the hypoglossal pacemaker work? The pacemaker has three major components. The first is the stimulation electrode, which is surgically implanted on one hypoglossal nerve (there are two nerves, right and left). The second is a sensing electrode, which is surgically inserted in the chest and detects when a person starts to inhale. The third is the electrical generator, which supplies battery power for the pacemaker. When the sensing electrode identifies the start of a breath, it signals the stimulation electrode to activate the hypoglossal nerve, which is the primary nerve to the tongue. This causes the tongue muscle to stiffen and resist airway closure, thus preventing apnea.
Although the hypoglossal pacemaker sounds like a dream come true for people with obstructive sleep apnea who have trouble using continuous positive airway pressure (CPAP), it has not been used in large numbers of patients to date. Two reasons have hindered widespread use––cost (about $30,000) and lack of data showing effectiveness in patients who are severely obese. This is important because two-thirds of people with obstructive sleep apnea are overweight or obese. The insertion procedure is not complicated, although it requires a brief surgical procedure and follow-up to adjust the pacemaker settings. However, as more experience with it accumulates, usage of this novel therapy may increase.
Central sleep apnea also may be amenable to pacemaker treatment. Central apnea frequently is observed in patients with heart failure, and is difficult to treat. Recent studies show that a pacemaker inserted through a central vein, in a manner similar to placement of a heart pacemaker, can stimulate the phrenic nerve, which controls contraction of the diaphragm. This pacemaker senses the absence of any effort to breathe and then activates the phrenic nerve. The phrenic nerve then causes the diaphragm to contract, initiating inspiration. The studies show that central apneas decrease and sleep quality improves. Although the pacemaker is not yet available in the United States, FDA approval may be forthcoming.