Some people have much more trouble with equaisation than others. Some divers need to equalise every meter in the first 10m, others once … One reason can be small Eustachian tubes. What is actually happening to a “small” tube compared to a “bigger” one in depth, which makes equalisation so difficult or impossible? Are the tubes collapsing (sticking together) at some point and can’t be opened by an equalisation maoevre anymore? And is there anything (any exercise) that can particularly help someone who has small Eutachian tubes to facilitate equalisation?
Narrow tubes dont let much air passing efficiently, slowing down the equalization process.
The tubes can collapse and stick together like you said, mainly when you dont equalise fast enough and slowly slowly there is a negative pressure building inside the middle ear, at some point his negative pressure will get the tube’s walls to stick together. technically it is possible to open them again by doing an aggressive equalization manouver but the chances to create an injury by doing so are very high, so the only thing to do in this situation is to turn around and swim to the surface. the block will be gone spontaneously in just a few seconds without you doing anything.
One thing that can help is to use a tool called otovent. originally invented for the treatment of glue ear and middle ear infections it is proving very useful to help freedivers with their equalization. With the right exercises and a lot of practice this can solve the problem completely.