The troll is going to post some objective info on pulmonary embolism and DCS... Which confirms most of what we have discussed so far....
http://www.mtsinai.org/pulmonary/books/scuba/sectionj.htm
SCUBA DIVING EXPLAINED
Questions and Answers on
Physiology and Medical Aspects of Scuba Diving
WHY DOES PULMONARY BAROTRAUMA OCCUR?
There is no doubt that pulmonary barotrauma results from unequal air pressures across the lung. But why does it occur in some people and not others. Is it always from a breath-hold ascent?
Although breath-hold ascents account for some cases, there are also cases of barotrauma where the divers are certain they never held their breath. There are two explanations for this latter group. First, some divers probably have abnormal lungs and don't know it. Such changes as subpleural blebs and bullae (abnormal air pockets in the lungs) can often be demonstrated by chest CT scanning or even a plain chest x-ray in people with no respiratory symptoms or problems. After one diver suffered major barotrauma, a chest x-ray that was done before the dive was reviewed; it showed a large bulla, or abnormal air space with thin walls. Probably a certain percentage of people have such "weak lungs" (for want of a better term); these weak lungs may cause them no difficulty except when exposed to slight pressure changes that would not affect normal lungs.
Still, there are apparently other divers with completely normal lungs, who are confident breath was not held, yet who still suffered pulmonary barotrauma. These events are difficult to explain, and are fortunately rare (as is pulmonary barotrauma in general). Pulmonary barotrauma remains a definite, albeit small, risk of scuba diving.
Greatest Risk of Expansion Barotrauma is Near the Surface.
Barotrauma correlates with both increase in pressure in the lungs and 'over stretching' of the lung tissue. Experiments in dogs undergoing rapid ascent in a chamber showed that the lungs can withstand much higher pressures (before barotrauma occurs) if the chest cavity is bound and 'over stretching' is prevented (Schaefer 1958).
Although both over stretching of lung tissue and the pressure of expanding air are factors favoring lung trauma, pressure seems to be the major one. The pressure difference across the lungs (from inside to outside) that is the threshold for experimental barotrauma is about 80 mm Hg; this can occur with a breath-hold ascent from only four feet! The pressure difference (and risk of barotrauma) is obviously much greater with breath-hold from greater depths. During a breath-hold ascent from 33 feet the lung volume would try to double, almost guaranteeing barotrauma if breath were held at or near the diver's total lung capacity (Figure 3).
CONCERNING DIVE TABLES
Understand then, this is just a for the real world. What really happens is far more complex than any , which is one reason why any should be tested as widely as possible. By assuming uptake and excretion times for the various compartments, Haldane and others were able to arrive at tables for avoiding the bends which work in practice. And keep in mind that "work in practice" means most of the time, not all the time.
CONCERNING DCS
The mechanisms that cause DCS are not well understood, and bubble detection is simply a technique to monitor one aspect of the problem in a group of volunteer divers. That the tables work when tested on a small group does not, of course, guarantee that they will work for everyone, all the time. The population of recreational scuba divers is simply too diverse for any table to be tested for all the varying characteristics of people (age, weight, percentage of body fat, level of fitness) and dives (depth, time, rate of ascent, water temperature, visibility levels, etc.) that will encompass all situations.
Since different people can react differently to decompression, no table can be considered 100% safe. The standard dive table is thus only a conservative guide to safe diving for the whole population, and not a personal safety guide for each diver. It is a fact that some people diving within standard dive table limits have developed DCS.
There is no perfect table, nor will there ever be. Nonetheless, years of experience with available dive tables shows they are far better than nothing and, miraculously, seem to keep most divers from ever getting bent. Only a few hundred DCS cases are reported to DAN every year, which is a small number for such a potentially hazardous activity that is practiced millions of times a year. (See Section P.)
