We apply different kind of breathing in kata. The other methods introduced concentrate on exhaling but this breathing concentrates on "holding the air".
Luckily, I found a website explaining the kata breathing in detail, which quotes from Komorizono Masao Kendo Kojutsuroku (Oral Statements of Masao Komorizono).
Unfortunately, this is only available in Japanese on the web, but Kendo World Vol. 4.1 also introduces this in one of the articles called "Breathing in kata".
This is the outline of the kata breathing.
* Seika-tanden: It is a part of our body where it is said that the source of energy (ki) is located (or created). It is at about three fingers below the belly button.
Basically, when we get close to your opponent, we do not want to show our opponent when we breathe in and when we breathe out. Why?
We are very vulnerable when we breathe in and out. That is why we breathe in when we are far away from our opponent and breathe out very slowly.
I suggest that you should worry about the breathing in kata when your kata is improved. At the beginning of learning kata, you are too busy to remember the forms. My suggestion is to concentrate on learning the forms first.
Hope this helps.