The molecular pump in the inner ear?

2012 March 14
by Daniel Lakeland

My previous post on Otitis media explains how the cause of ear pain is usually reduced pressure in the middle ear resulting in the external pressure pushing the eardrum inward and causing pain.

The question then arose in my mind, "what causes the reduced air pressure?". In the context of an inanimate pipe or tube, the pressure in the interior stays constant unless you have a pump that sucks out the contents. I noticed as I was clearing my ears multiple times per day that it didn't take long before a cleared ear became a painful one.  This suggests that something is pumping down the pressure in my ear at a relatively rapid rate (a significant fraction of an atmosphere per hour or so perhaps).

So far, I don't have the answer, but I can imagine some hypotheses. Perhaps some blog reader knows the right answer?

Candidate Hypotheses:

  1. The inner ear epithelia respirate through direct absorption of gas from the inner ear rather than primarily through oxygen absorbed from capillary beds. This uses up the oxygen, and could cause up to a 20% decrease in pressure (from the 20% oxygen content of air).
  2. There are capillary beds in the inner ear, but they are actually absorbing oxygen onto the hemaglobin and carrying it away (again up to 20% reduction in pressure).
  3. Everyday actions such as chewing, swallowing, drinking, sniffing and soforth both pressurize and depressurize the ear, but when the eustachian tube is swollen, the depressurization direction becomes like a ratchet as lowered pressure squeezes the tube closed, causing progressive depressurization.

Of course, it could be a combination of these, but I have a tendency to think that something is actually chemically pumping out the gas molecules and that this mechanism contributes nontrivially to the depressurization.


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