I suppose the theory is based on the fact that it is damned difficult to
get your shoes back on after a long-haul flight - we do, in practice,
swell up, even if it is not immediately obvious why - indeed a balloon
full of water would not swell up.

Theorising: Lowering the lymph pressure might reduce the drainage rate
but it wouldn't lead to swelling per se, as the volume built up the
pressure would rise and increase the drainage rate again.  So I wonder
whether it is due to the skin's inability to retain the pressure
differential between the lymph and the air.  Or perhaps it might be a
dynamic effect due to *changes* in pressure, eg the lymph volume grows
while the pressure is low, but causes trouble when the pressure rises
again. Or a final theory, the flow of lymph is a diffusion process and I
know it takes a hours for pressure changes to diffuse through the tissue
and reflect in pressures within the tissues, so perhaps tissues swell
because of high pressure of absorbed fluid.  In which case it would as
Sandy says have no implications for ductal lymph and drainage.  But that
still doesn't explain why it acts like there is a compressible fluid, a
gas, present in the first place.

I don't know whether this helps, but I understand that the pressure in
an airliner cabin is roughly equivalent to that of an unpressurised
cabin at about 8000 feet altitude.

I don't know if the problem is real or imagined but if it is real I
imagine that the duration of the flight would also be relevant factor.

If you are worried, you could wear a compression sleeve on the arm as a
prophylaxis during the flight.

Tim Jackson

What makes you think I am a little nervous, Alan??  In fact, I never
thought about the altitude of some cities.  Well!  You just canceled
that trip for me!  But thanks anyway.  I know you just want to be
helpful.  I need to give up on those mountains anyway.  I'm just
grateful I saw most of the places with mountains before bc.

Bea