Here's an article I wrote for some magazine a few years back- a good refresher for us, and maybe new info for some. We wont be diving that deep necessarily, but this technique is really the best way to dive, even from the surface.
How to Equalize at Depth
This is (hopefully) an easy to understand description of 1: why it becomes hard and/or impossible to equalize at greater depths, and 2: how to overcome this barrier.
As freedivers, we descend with our heads down, and the air in our lungs above the areas that we need to equalize: our sinuses, mask, and eustachian tubes. Most of us start out using the Valsalva technique, in which we push air down into our head with our diaphragms (since air rises in water). This works to approximately 30 metres, then the diaphragm is not capable of pushing the air down beyond this point (there are individual exceptions, but this applies to most people). The result is that the diver has a few choices; continue deeper and rupture the eardrums and sinuses and get a mask squeeze, turn head-up so that air will rise into those airspaces, or abort the dive. Since we want to dive deeper and with the least expending of effort, none of those are good options.
There is a combination of techniques developed by Eric Fattah called “The Frenzel-Fattah” which is a much more efficient method of equalizing, and will also allow us to dive extremely deep.
After your breathe-up, just before you tuck and dive, pull your head back, lower your chin (keeping your mouth closed) and blow into your mouth until your cheeks are full and stretched. Close your epiglottis (the valve in your throat that leads to your lungs), relax your head into proper profile, then dive. The valve stays closed until later. Use the air in your cheeks to equalize your ears, mask and sinuses. If done properly, you will easily dive to 20+ metres using only this air in your mouth. If this is as deep as you want to go, then fine.
If you want to go deeper, then there will be a point where there is no air left in your mouth with which to equalize, so you must fill your mouth again. This depth varies among individuals, but most of us need to refill our mouths at approximately 25 metres. The important point is that it is done at a depth where you can still fill your mouth to the max, using your diaphragm. If you wait until deeper, you may not be able to fill your mouth, and this will result in a shallower max depth. If you do it too shallow, you will also limit your max depth. There is a way to pull air out of your lungs using your mouth like a plunger (reverse packing), but it will not fill your mouth properly and it takes effort, so it is much less efficient.
Once you are at the depth where you will refill your mouth, arch your head back, lower your jaw (mouth closed of course) and blow into your mouth until your cheeks are full. Relax you neck back into it’s normal profile and continue your dive. If you are physically capable, there will be enough air in your mouth to equalize 80+ metres! An added benefit is that you have initiated a faster dive reflex by shunting blood out of your limbs and into your chest cavity earlier in the dive.
This is an advanced technique that takes practice. Practice using the surface mouth-fill first to get comfortable, then work your way down. You can try a refill at 10 metres to get a feel for it at depth. Also, since you are shunting blood earlier in the dive, you must be careful with the possibility of lung squeeze. If your chest compresses beyond it’s ability, you can get hurt, so work your way down the ladder slowly. Don’t go from a PB of 42 metres to an attempt at 50 metres (as I did in my first contest). Even if your PB is 42 metres and you haven’t dived to beyond 30 metres in 3 months, don’t attempt to hit that PB again for a while (as I did in my first competition). Your lungs’ flexibility will come back, but not necessarily in one or two days. Go slowly and listen to your body….feel what’s happening during the dive. It becomes more difficult to fell what’s happening in our bodies beyond 30 metres, due to narcosis and CO2 levels.