Hello,
Regarding the Vacuum Effect, it is more related to pressure rather than gas imbalances.
from my manual:
Gas levels, mainly oxygen and carbon dioxide are continously balancing themselves in the body, between the lungs and body tissues. The body draws 02 fro the lungs, as it requires. The 02 concentration (partial pressure) in the lungs of a descending diver increases due to the increasing hydrostatic pressure. As the brain and tissues use 02, more 02 is available from the lungs while he is still descending. This all works well as long as there is 02 in the lungs and the diver remains at his descended level. The problem is in the ascent. The re-expanding lungs of the ascending diver increase in volume as the hydrostatic pressure decreases, resulting in a rapid decrease of 02 concentration (partial pressure) in the lungs to critical levels. The balance or gradient that forced 02 into the body is now reversed. Thus, the vacuum effect is really a net flow of 02 from the body back to the lungs. It is most pronounced in the last 33ft below the surface, where the greatest relative lung expansion occurs due to the greatest relative change in pressure. This is the danger zone where unconsciousness frequently happens. The blackout is instantaneous and without warning. It is the result of critically low level of 02 which, in effect, switches off the brain.
About the Garas, they do get more flexible with age but you also get stronger... They are a good fin and the Super Ochio is a good mask.
The Sphera mask is not the best made mask on the market. It has plastic lenses that scratch easily and you need to treat it carefully. However, it has great view and is very low volume. I use it for performance dives that are deep and long duration and I use my Omer Alien for everything else.
The fluid filled goggles are usually filled with contact lens fluid but you can use salt water, its almost the same material as tears.... They work very well, you can see amazingly well. Eric Fattah has a line of fluid filled goggles and nose clips...
A wetsuit and weights - 3mm and about 6lbs. Why? its your safety net. If you find yourself deep and needing to bail out of the dive you can throw away your $45 belt and gain some bouyancy from the suit. If you are way, way deep you are already negatively bouyant and will need everything working for you. The wetsuit, and the other gear I described are all part of your safety kit. You wouldn't go to the moon without all your gear and your space suit..... At 100ft plus deep you might as well be on the Moon. It is a very specialized place and you are just visiting - it is hostile and can kill you if you stay to long or aren't correctly prepared.....
Breathing up - Basic Breathup
deep full inhale about 3secs
Pause while holding 2secs
Long, slow release for 15 secs
Why? Heart rate increases on inhale, decreases on exhale. So concentration on slowing heartrate (bradycardia) while being inactive and breathing fully will saturate blood and tissues with 02.
So, after doing the above cycle for 2-2.5 times the duration of the previous dive you peak inhale and dive.
Why 2-2.5 times? You need to "normalize" gas imbalances including Nitrogen (!) as you do your 02 saturation.
Packing is something you build up to. You can stress your intercostal muscles if you don't go slowly and get used to it. Through packing you are trying to hold up to 2liters of pressurized "extra" air in your lungs. You start by sitting down and doing a peak inhale, then gulp 2-3 extra bits of air - hold and stretch your ribcage (arms over head) gently for a few moments, and release. Build up over a couple of days to ten packs.....
Of course, now you feel like a balloon on the surface after a full breath up and packed lungs so you need to get down to 1ATA to start compressing all that air and make it manageable....
Along with all this technical stuff comes the practice of 02/C02 tolerance tables to increase your durations.
The single most important aspect to freediving that you can internalize is the Mammalian Diving Reflex. If you understand how one initiates that altered state of physical and mental being, the very specific process of getting into that state of reduced heart rate and heightened mental awareness, one can apply it at will and get very, very comfortable with long deep swims.
The diver who is enhanced through Tolerance training and technical awareness when the "Reflex" is initiated will have incredible performance....
Lungfish