Can using a CPAP machine cause decompression sickness (aka. the “bends”)?
No. The following discussion outlines why.
As they descend underwater, scuba divers breath air compressed to the same pressure as the surrounding water. For example, at sea level they breathe air at a pressure of 1 atm, while at a depth of 33 ft. they breathe air compressed to 2 atm.
While breathing this higher pressure air, some of the nitrogen in the air gets absorbed into body tissues at the high pressure due to Henry’s law. When the diver ascends, this nitrogen must be removed from the tissues or it will expand within them as pressure drops, causing decompression sickness. By limiting the amount of time the body is exposed to the high pressure nitrogen, divers limit the amount of nitrogen absorbed, ensuring the nitrogen content is such that it can be exhaled during ascent and between dives. They calculate and follow a “theoretical No Decompression Limit” that specifies how long they can remain at specified depth before absorbing too much nitrogen.
Continuous Positive Airway Pressure (CPAP) is a therapy for obstructive sleep apnea. Users of the therapy wear a mask that supplies slightly compressed air while they sleep. This compressed air forces their airway open to enable unobstructed breathing.
Because CPAP machines deliver compressed air, excess nitrogen might get absorbed into users’ tissue. But is it enough nitrogen to cause concern?
Infinite No Decompression Limit
To arrive at this answer, I first modeled a CPAP user as a scuba diver diving to the depth that their CPAP machine’s pressure is set to, and then calculated the theoretical No Decompression Limit in minutes for that depth using the Haldane decompression model.
I used R’s “scuba” package for a simulated dive to 12 cm, which is the pressure of air delivered by a friend’s CPAP machine:
At a depth of 12 cm, the reported No Decompression Limit is infinite. Therefore we conclude that CPAP users are not at risk for decompression sickness.