Introduction

Sleep apnea is surprisingly common. It affects between 2% and 4% of middle-aged US adults. It's associated with daytime sleepiness, as well as an increased risk of high blood pressure and cardiovascular disease. Most cases are what is called obstructive sleep apnea, where there is partial blockage of the airway by the soft palate during sleep. (The links given below describe obstructive sleep apnea and it's treatment.) The other form, central sleep apnea, is related to decreased regularity of nerve stimulation of the diaphragm.

People with sleep apnea, whether it's obstructive or central, usually have periods of slower or faster heart beats during the night. A recent study from France, reported in the New England Journal of Medicine, was done after it was noticed that some patients who had a pacemaker had reduced nighttime breathing problems. The investigators wanted to test whether setting the heart rate a little faster would help reduce the symptoms of sleep apnea.

What was done

Fifteen patients were selected who had received a pacemaker at least a year earlier and who had problems suggestive of sleep apnea -- e.g. excessive snoring, daytime sleepiness, and frequent waking at night. Polysomnography¹ confirmed the diagnosis.

None of the patients were dependent on their pacemakers, which had been implanted for harmless but symptom-producing episodes of slow heart rate (sinus bradycardia).

The patients spent 3 consecutive nights in the sleep laboratory, undergoing polysomnography. The first night represented a baseline, with their pacemakers set to a rate of between 55 and 60 beats per minute (bpm). The next night they were randomly assigned to one of two procedures, which were reversed on the third night.

The first procedure, called 'no-pacing', involved programming the pacemaker to stimulate only the heart ventricles at a rate of 40 bpm; this meant that for most of the time a spontaneous rhythm, above 40 bpm, was recorded. The other procedure, called 'pacing', involved setting the heart atria to beat at a rate about 15 bpm faster than the patient's average nighttime heart rate at baseline. The number of episodes of apnea and hypopnea (reduced respiratory function) in each phase were counted.

The results of the study

The average age of the 15 patients was 69. There were 11 men and 4 women; 8 patients had the central type of sleep apnea, and 7 the obstructive type.

The results of the breathing disturbances during sleep are given in the table below:

	No-pacing Phase	Pacing Phase
Average heart rate (bpm)	51	72
Total sleep time (min)	321	331
Apnea/hypopnea (number/hr)	28	11
Hypopnea (number/hr)	9	3

The average heart rate in the no-pacing phase represented a natural, spontaneous heart rate for these patients. In the pacing phase, it was 21 bpm higher, due to the atrial pacing set by the program. It can be seen that atrial pacing was not associated with any reduction in total sleep time.

There were significant reductions in the number of apnea and hypopnea episodes with atrial pacing, compared with the no-pacing, or spontaneous heart rhythm, phase.

There were no other relevant differences between the results of no-pacing and pacing in these 15 patients.

What does it mean?

The investigators who conducted this study think that the good results obtained are due to an effect of the atrial pacing on the function of the vagus nerve. Patients with central sleep apnea often have a lowered blood oxygen level, a slow heart rate, and a low blood pressure, all of which are usually associated with increased activity of the vagus nerve. Atrial pacing overcomes this sort of vagal over-activity. The drug theophylline, which has the ability to block vagus nerve activity, has a beneficial effect in central sleep apnea.

The way in which atrial pacing benefits obstructive sleep apnea is not yet explained. However, the beneficial effects were present equally in this group of patients, so that further work is clearly needed.

Putting in a pacemaker is hardly likely to become an acceptable treatment for sleep apnea. However, these findings, provided they can be confirmed, clearly suggest that there may be other, simpler, ways to get the same sort of results, perhaps with a new medication. This offers new hope to sleep apnea sufferers.