Posted 16 May 2004 - 04:05 PM
The threads in this section are designed to generate thoughtful discussion on medically related topics, and this thread proves that is happening. These are great comments and discussions from very thoughtful and experienced individuals, and should be read by all.
In terms of the many excellent points made, I will add the following. I agree with Grant that optimal technique (bouancy control, ascent rate, etc) is by far the best that someone can do to protect themselves from a relatively low incidence, but highly significant if it happens, occurrence (getting bent). The newer the diver, the scarier the potential of getting bent, due to the unknowns. The previous comments and suggestions were not necessarily directed to the most experienced, but to those still learning and perfecting their skills. On that note, I believe that giving sound advice, a recipe for success if you will, that can be easily understood and followed, best helps the most people, even if not exact to the experienced or technical diver. The concept of a deliberate slow ascent, multiple stops along the way, safety stop at 20 ft for 1 min, continue for 3-5 min at 15 ft, then a VERY SLOW ascent to the surface were the major points made. Thanks to all for emphasizing the importance of these points.
I likewise agree that it is not the absolute volume of bubbles that develop, but where they are located, that most influences outcome. A small amount of bubbles in the spinal cord area are much worse that more bubbles in the venous bloodstream going to the heart and lungs. However, since we don’t have a bubble monitor with us, we derive indirect information from total bubble measurement with various ascent profiles, then extrapolate. Best condition is that nitrogen stays in solution, off loads in the lungs, and all is well in OZ.
As for the aspirin controversy…. I see things a little differently, Grant. In medicine, we often prescribe treatment if it is known to be beneficial, while at other times we suggest treatment if it doesn’t cause harm, and may help. I agree that firm data on aspirin and bubble formation/ propagation/ platelet activation/ microclot formation is not clear. Probably never will be. Hard to do the study. I do know that platelets get activated by exposure to abnormal surfaces in the blood stream (like a torn blood vessel, cholesterol plaque, and maybe a nitrogen bubble fits here). I know that once activated, platelets attract their buddies, and they set up a sticky platelet commune. This obstructs blood flow in that area. We give supplemental oxygen to someone who may be, or is bent with a goal of increasing oxygen delivery to downstream tissue at risk for hypoxia (lack of oxygen). I feel that “pretreating” someone with a relatively benign drug that may reduce platelet activation and therefore may support better blood flow if bubbles develop in the circulation, is helpful.
When I look around, I see many divers with risk factors for coronary artery disease, organ dysfunction, microvascular perfusion abnormalities, and other related conditions (age > 40, male, smoker, high cholesterol, hypertension, stress, diabetes or kidney conditions, and others). People with risk factors for heart disease are told to take aspirin daily as a prophylactic measure, and those having a heart attack are told to take an aspirin right after they call 911. This is to suppress the platelets from forming a plug in the coronary artery and causing further obstruction to blood (oxygen) flow. Those divers with the above conditions(whether they know it or not) will be somewhat protected from the exertion of diving and the risk of tissue ischemia by aspirin. I think that it makes sense to add protection, especially to these people while doing strenuous work in water. Granted this may or may not have anything to do with developing the bends, but it is a “two-fer”. I see aspirin not as a replacement for optimal diving technique, but as a possible additional safety measure while we all strive to reach that optimal diving technique. I respectfully disagree that the “pain killer” effects of aspirin will mask a clinically significant case of DCS. Given the choice, I choose to believe that aspirin may have more of a potential benefit (suppress platelet activation) than negative effect (delay diagnosis of DCS).
Nitric Oxide has been mentioned. A very cool substance. Brings back memories of “The Abyss”. I actually wrote a proposal for NO use in bubble scavenging many years ago. That proposal was for its use in cardiac bypass procedures as well as decompression treatment. Unfortunately the study went the way of many… back shelf. If not for cost and shelf life, NO would be a great substance to have at all chamber locations. Similar to oxygen (and aspirin), if it doesn’t’ hurt, and may help, why not give it. There are some multi million dollar studies now underway on the east coast investigating NO in hyperbaric medicine. I have read the studies that report exercise 20-24 hours pre-dive being protective, but NO plasma half life is measured in seconds, so I am not convinced that NO is the key to that data. It may have more to do with how the body responds to exercise. Recovery period washes away metabolites, then the rebuilding phase delivers glucose to the cells. Slow vs fast uptake tissues may have blood flow affected around the time of exercise, so store less nitrogen during diving. Nitric Oxide is just a current "hot topic", so if someone mentions it, they increase their chances of getting the article accepted for publication.
What would be really awesome from this thread is to develop a clear, concise guideline for ascent rate for recreational divers, applicable to both new and veteran divers. Many have contributed to that goal, and I deeply appreciate the info. I will take a stab at summarizing, and others can fine tune.
“SingleDivers.com Ascent profile for optimal safe diving”;
1. Before the dive, be rested and hydrated
2. Calculate time/ gas needed for bottom time and ascent
3. Safely go to depth and enjoy yourself.
4. Be aware of gas consumption, ascent requirements and reserve
5. Ascend no faster than 30 ft per minute
6. Stop for 1 minute at ½ max depth
7. Continue to ascend no faster than 30 ft per minute
8. Stop for 1 minute every 15 feet (½ atm)
9. Stop at 20 feet for 1 minute
10. Continue safety stop at 15-20 ft for 3-5 minutes
11. SLOWLY ascend to the surface
12. Replenish fluids while telling dive stories
So for a dive to 100 ft, this would mean;
Ascend at no more than 30 ft/ min to 50 feet, then stop for 1 min.
Ascend at no more than 30 ft/ min to 35 ft, then stop for 1 min
Ascend at no more than 30 ft/ min to 20 ft, then stop for 1 min
Ascend to 15 ft, then stop for 3-5 min
DELIBERATELY SLOWLY ascend to the surface trying to take at least a minute to do so.
This ascent process took 10-12 minutes, not a bad investment for safe diving.
Diving; My zen space.
