As many as 60-80% of clusterheads have apnea and routinely stop breathing in their sleep according to this study (cache) and this other study (cache). Sleep apnea is most likely to occur in REM sleep, which is also the most likely time for a cluster headache to occur during sleep. In apnea, oxygen levels in the blood may drop to 80% of normal (sometimes lower). Breathing Oxygen at a high flow rate is one of the more effective ways to abort a cluster headache attack; while oxygen is a vasoconstrictor, it may also act by reversing the effects of apnea or poor oxygenation from other causes.

The use of CPAP machines to treat apnea has a limited effect on cluster headaches; reports from online message boards indicate that some patients experience relief, while others do not improve. Some sufferers also report that sleeping in a semi-upright position (reclining chair) can be of benefit, presumably this helps keep the airways open while asleep. It is possible that the apnea that many clusterheads suffer from is not Obstructive Apnea (caused by physical blockage of airways) but is caused by a neurological mechanism (Central Apnea). Serotonin and other neurotransmitters are involved in the regulation of breathing, and it is widely accepted that clusterheads have a disorder in serotonin regulation.

Nitric Oxide and Apnea

One study of obstructive sleep Apnea found that Nitric Oxide levels are lower in people with sleep apnea (abstract (cache)).

Alcohol consumption is considered a risk factor for sleep apnea, and is a well known trigger of cluster headache (probably through the stimulation of Nitric Oxide production. This is a curious contrast to the fact that Nitric Oxide is often cited as a bad actor in the triggering of clusters, and suggests a more complex dynamic - perhaps low NO contributes to apnea, and apnea triggers an alarm mechanism that leads to the emergency release of NO.

CGRP

Calcitonin Gene Releasing Peptide CGRP is also linked to apnea.

A Neglected Disease in Clusterheads?

Apnea increases the risk of heart attack and other serious problems. If the research is correct and 60-80% of clusterheads do have apnea, then it is a seriously under-treated problem. It is not clear if Preventive medicines reduce apnea in clusterheads ... the ideal treatment would reduce or eliminate apnea and keep people breathing steadily through the night.

Most doctors reccomend that overweight patients with apnea lose weight - even losing a few pounds has been associated with a reduction of apnea. Sleeping on your side (instead of back or stomach) also lowers the risk of apnea (abstract (cache)).

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