Well I'm by no means an expert, but I'll give a couple of these a shot - feel free anyone to add anything, change anything or just plain make fun of me
4. Q:What are co2/o2 tables?
A: A table is set sequence of apnea events, lasting for a certain duration with a certain rest time in between. For example, a basic table may consist of five breath holds lasting 2 minutes, with a rest time in between each hold of three minutes.
CO2 tables are designed to build up the levels of CO2 in your body (called "hypercapnia"). CO2 levels are your primary trigger for the urge to breathe, and also determine when you start getting contractions. A typical CO2 table has a constant hold time (usually half your maximum static, say two minutes) with a decreasing rest time (say, starting with 2 minutes rest, then halving the rest in between each static). This table may then be carried out as:
Breathe up
Hold 2:00
Rest/Breathe Up 2:00
Hold 2:00
Rest/Breathe Up 1:00
Hold 2:00
Rest/Breathe Up 0:30
Hold 2:00
Rest/Breathe Up 0:15
Hold 2:00
This would be called a "two minute CO2 table". There are also other variations on the table (ie hold until a certain number of contractions, take one breath, then hold until the same number, take one breath, etc).
An O2 table is designed to lower the levels of oxygen in your body, that is, to get you hypoxic. In contrast to a CO2 table, the rest periods are ususally constant (say two minutes) where the hold time increases (say starting at two minutes, and then adding a minute each time). For example:
Breathe Up
Hold 2:00
Rest/Breathe Up 2:00
Hold 3:00
Rest/Breathe Up 2:00
Hold 4:00
Rest/Breathe Up 2:00
Hold 5:00
is an example of an O2 table. Variations on O2 tables include "negative tables", which consist of an O2 table done after a full exhale (ie on "empty lungs").
11. Q:What is equalizing? What are Frenzel technique, BTV, Valsalva? How often should I equalize?
A: As a diver descends, the pressure changes experienced cause the ends of the Eustacian tubes (contained in the inner ear) to seal up. If further pressure changes are experienced, this cause cause severe pain and a rupturing of the ear drum. To compensate for this, the pressure in the Eustacian tubes must be equalised - conciously on the descent, and generally automatically on the ascent.
Basic equalisation (known as the "Valsalva" method, after its invetor) is carried out by pinching the nose, then trying to forcibly exhale through the nose. A "popping" feeling should be felt in the ears if this occurs properly.
Many people (especially beginners) find equalisation a hurdle to cross when they first start freediving. This is due to individual differences in physiology. Because of this, there are multiple known techniques for equalising the ears. BTV or "hands free equalisation" is exactly that - a way to equalise without pinching the nose. Frenzel equalisation is another method (involving placement of the tongue) which is generally considered more effective than Valsalva.
Equalisation should occur
before any pain is felt. This means (generally) every few meters in shallow depth, then less as the pressure changes are more acute at depth.
When significant depths are reached, the volume of air in the lungs is compressed to the size that they would be on land if all the air was forcibly exhaled from them. In this instance, it is not possible to get the required pressure into the mouth to equalise. Because of this, another technique known as the "mouth fill" technique was devised. At a shallower depth than where residual volume is reached, the mouth is filled up with air from the lungs. The diver then closes off the soft palate (located in the back of the throat) to hold this air in the mouth (which is at a higer pressure than in the lungs). Using a mouthfill like this at an appropriate depth has enabled many divers to still equalise to extreme depths.