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Speeding the heartbeat with
a pacemaker relieves some cases of sleep apnea.
How a pacemaker might reduce the severity of the sleep disorder is uncertain,
but the study's authors suspect that the implanted device counteracts
the "decelerating" part of the nervous system.
People with sleep apnea stop
breathing dozens of times each night, causing them to gasp for breath.
The condition is conservatively estimated to affect from 2%
to 4% of middle-aged Americans, and is particularly common
among obese people. Sleep apnea has been linked to daytime sleepiness,
as well as an increased risk of high blood pressure and cardiovascular
disease.
There are several treatments
available for sleep apnea, including surgery and a therapy called CPAP,
or continuous positive airway pressure, in which a facemask is used to
introduce a gentle stream of air to keep the airways open during the night.
Researchers noticed that breathing
disorders improved in several patients who had received a pacemaker to
correct an abnormal heartbeat. The researchers decided to see whether
setting a pacemaker to speed the heartbeat might improve sleep apnea.
The study included 15 patients
who had a pacemaker implanted to correct a slow heartbeat called symptomatic
sinus bradycardia.
Investigators found that episodes
of sleep apnea decreased significantly when the pacemaker was set to 15
beats per minute faster than the patient's average nighttime heart rate.
In 13 of the 15 patients, the apnea-hypopnea index -- a measure of the
frequency of slow or stopped breathing at night -- declined by more than
50%.
The observations are compatible
with their hypothesis so that patients with low heart rate during sleep
and sleep apnea syndrome could potentially benefit from a pacemaker for
sleep apnea episodes.
The researchers found that
a pacemaker relieved both types of sleep apnea -- central and obstructive
apnea. Obstructive apnea occurs when the airway becomes blocked by tissue,
such as the tonsils or the base of the tongue. Central apnea, in contrast,
occurs when the respiratory system stops working in the absence of a blockage.
The researchers speculate that
speeding the heartbeat with a pacemaker might improve central apnea by
counteracting increases in so-called vagal tone -- the part of the nervous
system that tends to slow down the body's activities.
Obstructive sleep apnea and
central sleep apnea are by and large different conditions. What is interesting
about the results is that the pacemaker seems to improve both types of
apnea.
The results are very surprising
as there is no clear prior hypothesis to explain why pacing should work.
The New England Journal
of Medicine February 7, 2002;346:390, 404-412, 444-445
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