Re: re: Cabin pressure controls

From:         Pete Mellor <pm@csr.city.ac.uk>
Date:         13 Oct 95 02:06:33 
References:   1 2 3
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Robert D. Seals" <rob@csc.albany.edu> wrote on Fri Sep  8 10:47:10 1995:-

> Normally, small openings inside the head (like the eustachian tube)
> allow fluids to pass back and forth to allow the pressure to
> equalize with cabin pressure. When you get some kinds of infections,
> maybe a cold, the tubes swell to the point that the fluids cannot pass.
> The result is unbelievable pain.
> ...
> So, maybe some planes have pressure problems, or maybe you are prone to
> colds.

Having any kind of upper respiratory tract infection is a good reason
for cancelling your flight, I have heard.

I used to suffer on the way down until I discovered scuba diving, and
the instructor explained the physics and biology of equalising pressure
in the various head cavities (particularly the middle ear).

Basically, the eustachian tube connects the middle ear (the space
immediately inside the ear-drum) with the back of the throat. Generally
(in the absence of serious blockage as might occur if you have a cold)
it allows air or fluid under excess pressure out quite readily, but
needs some persuasion to allow air back in, hence most discomfort is
experienced during descent rather than ascent.

The regulator on an aqualung delivers air to the mouth of a diver at
the same pressure as the surrounding water. Otherwise the pressure would
make it impossible to inflate the rib-cage, as I discovered in an abortive
experiment in the local swimming pool at the age of 12 with a new design
of snorkel using a flexible tube whose end was kept above water by a float.
At a mere 6 feet, both the tube and my chest were squashed flat! :-)

The diver's problem is to equalize the varying pressure in the mouth
and lungs with that in the ear and sinus cavities. Going up is no problem:
the eustachian tubes vent the pressure quite happily. While descending,
however, it is necessary to practise the equalisation drill for every
few feet of increased depth. The diver pinches his or her nostrils with
the thumb and forefinger using the grooves designed into the face-mask,
blocks the throat by placing the tongue against the soft palate (the mouth,
of course, is held open by the regulator mouthpiece) and blows out through
the nose. To the accompaniment of much loud squeaking of air in the
eustachian tubes the ears eventually "pop" and the pressure differential
vanishes, along with all the pain from external pressure on the ear-drums.

Without this, the pain below a few feet would be unbearable and the
pressure at even a fairly modest depth would rupture the ear-drum.
The equalisation manoeuvre is more difficult the greater the pressure
differential (which tends to flatten the the eustachian tubes) so the
rule is to descend slowly, and equalize often.

Since I learned this drill I have found both flying, and ordinary surface
diving while snorkelling, very much more comfortable. During the climb
just swallow. If necessary suck a boiled sweet or try turning your
head from side to side. During descent, practise the equalisation drill
every few minutes and don't give up until you feel your ears "pop".
People differ, and some will find this easier than others. A friend of
mine told me that he had never experienced discomfort while flying and
could "pop" his ears without even holding his nose. I have not found it
so easy, and for some reason my left ear is more reluctant to "pop" than
my right.

A problem from which young children frequently suffer is known as "gluey
ear". It is caused by blockage of the eustachian tubes and results in a
build-up of mucous in the middle ear. If not corrected it can lead to
temporary partial deafness and in severe cases could cause permanent damage
including burst eardrums. The treatment is a simple surgical procedure
to insert a grommet in the eardrum to allow the mucous to vent itself
externally. After a few months, the grommet is either surgically removed,
or drops out spontaneously and the tiny aperture in the eardrum heals.
Gluey ear normally disappears during mid-teens, and seems to be due to
the imaturity of the plumbing in childrens' heads.

It might be worth bearing this in mind if you want to take your kids on
a 'plane.

Pete
----

Peter Mellor, Centre for Software Reliability,
City University, Northampton Square, London EC1V 0HB
Tel: +44 (171) 477-8422, Fax.: +44 (171) 477-8585,
E-mail (JANET): p.mellor@csr.city.ac.uk
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