The sinuses are hollow spaces inside the bones of the
head. There is 1 over each eye, 1 in the cheek bone under each eye, and more
inside the head adjoining the nasal cavity. Since they are hollow they contain
gas and are subjected to the affects of Boyle's law. If you scuba dive and
the pressure in the sinuses does not change as you descend, the crushing
affect results in extremely sharp pain. The pain increases as descent is
continued until bleeding occurs. The blood will enter the sinus and may relieve
the pain to some extent. The diver may blow bloody strands of mucus from
the nose for several days after the dive.
The Skull showing some of the sinuses
The tubes to the sinuses are larger and shorter than
the eustachian tubes to the ears. Pressure is usually changed in the sinuses
automatically as the diver descends and ascends. If the tubes are blocked
by mucus due to a cold, allergy, or sinus condition, then a pressure differential
may occur. The sinuses will not collapse before they bleeding because the
bone is too strong for that to happen.
When you have a "head cold" it is the result of the sinuses
being stuffed with mucus from forcefully blowing the nose. The dull pain
in the cheeks and/or forehead is minute when compared to the pain caused
by a sinus squeeze. A sinus squeeze pain is super-sharp and usually prevents
the diver from descending further. Interestingly, if the squeeze is
to the sinuses at the rear of the nasal cavity (Submaxiliary) the diver will
be convinced there is something wrong with their teeth. The pain signal from
those sinuses are connected to the same nerves coming from the
teeth! Divers usually swear up and down they have to see their dentist
following a dive when a submaxiliary sinus squeeze is encountered.
Reverse blocks in the sinuses are rare because the tubes
are so large. If mucus started to block the exit of gas from a sinus upon
ascent, the mucus plug would simply be blown into the nasal cavity. There
may be slight discomfort as one ascends but the sinuses will usually clear
by themselves.
The biggest problem this author has with the sinuses
is when very cold water hits the the forehead. The brain freeze! Sometimes
a gloved hand has to be placed on the forehead to relieve the pain. It happens
if the wet suit hood does not meet the mask and there is a gap between the
two.
