Lung Squeeze vs. Lung Fluid
I have some experience with both.
Fluid ie. plasma filling your lungs is a response to the increased pressure at depth (usually at around 50m but it can vary quite a bit depending how much air you have in your lungs and your residual volume) to protect your lungs and other organs. This is a natural, if not a sometimes unnerving experience, which you can get if you do a negative pressure dive in the pool (with a spotter!). You may cough as if you have fluid in your lungs--which in fact you do.
Lung squeeze aka pulmonary oedema is a response to increased pressure as well, but it is harmful, damages your lungs, and, in extreme cases, can lead to secondary drowning.
I suffered from lung squeeze on a dive to 51 metres for which I had done inadequate warm-up and had not been close to the depth for more than a week (stiff ribcage, body loses adaptibility to pressure with time). The dive itself and my recovery was fine, but after a minute or two on the surface, my throat started to tickle, and then I had one of many coughing fits, spitting up a teaspoon of blood from time to time. Other symptoms later in the day included wheezing, feeling like I couldn't get a full breath, sluggishness and fatigue for the rest of the day.
My understanding of this, as Kirk Krack and a doctor explained it to me, was that as the pressure increased, my rib cage stopped collapsing at a certain point and a negative pressue grew in my lungs. In an ideal dive, plasma equalizes the pressure and the rib cage collapses much more. In a lung squeeze, the aveoli are squeezed (flattened) and bleed to equalize the pressure (liquid being non-compressible). Unfortunately, they remain coated with blood long after the dive is over and are unable to perform their oxygen transfer job. Effectively, they are out of commission, until the blood is coughed up or reabsorbed somehow. This condition is not common enough for Doctor's to recognize it right away, but I'm pretty sure that's what happened to me. I can see how this could lead to secondary drowning. Aveoli coated in blood prevent the gas exchange you need for oxygenated blood.
So my advice to everyone is that as freedivers benefit from the knowledge of deep divers (in my case, Eric Fattah) and realize gains in depth much faster than those before us, is to be aware that there may be problems with going to deep too fast other than shallow water black out. So take it easy, give your body time to acclimatize to each depth. And keep your aveoli healthy.
I took a month off from diving to depths deeper than 30m and even then took it slowly to make sure things were okay. Better to freedive when I'm 64 than to drown or wreck my lungs for every.
By the way, as far as I know, plasma in your lungs is not a "technique" invented by Pipin, it's just a natural adaptation of the body.
Pete
www.holdyourbreath.ca