silent bubbles

[edylchtims]

In a conversation with a tech diver regarding extreme depth dives on air, the guy mentioned silent bubbles as a possible effect of a deep dive. I have never heard of silent bubbles. Can you explain?

 

[SteveAD]

Silent Bubbles are also known as asymptomatic bubbles. There has been significant research done using doppler ultrasound equipment to detect bubbles in a divers bloodstream post dive. These bubbles appear in upwards of 60% of divers after multiple dives without any symptoms of DCS. Further research has shown that the 15 foot safety stop seemed to reduce the incidence of silent bubbles, and deeper stops while still on a "no deco" profile reduced them even more.

 

[TSandM]

As Steve said, one of the surprises of Doppler investigation of divers was that many divers have detectable bubbles after a dive, without reporting symptoms, or certainly not clear-cut symptoms of classic DCS. This has led to the idea of "subclinical" DCS, manifested by fatigue, "flu-like symptoms" and other vague complaints that suggest that decompression stress exists even before obvious joint pain or neurological complaints occur. It is clear from research that there is not a one-to-one correlation between degree of bubbling and degree of symptoms. Some patients with a lot of bubbles remain asymptomatic. If I remember my reading correctly, however, no diver with no detectable bubbles was ever found to be symptomatic of DCS (although AGE is something quite different).

Silent bubbles are a big part of the reason why most modeling of decompression nowadays takes bubble mechanics into consideration, and why most people are now recommending some form of deep stops to control bubble growth.

 

[Mr Carcharodon]

As noted, by TSandM, fatigue is a symptom of sub-clinical DCS. Richard Pyle who empirically introduced deep stops based on observations from his dives noticed reduced fatigue on dives that used deep stops. Please do note this type of leading indicator and then act upon it to reduce your risk. Things you can do to reduce your risk are: deep stops, ascents of 10 feet per minute from half max depth to the surface, longer hangs at between 30 feet and the surface, and reducing the NDL times for a given depth.

Safety stops are of course decompression stops that were renamed out of some sort of perverse caution. Assuming you have run up to or past the NDL extending the hang at 15 fsw is highly advised. Also note that the NDL limits on the PADI/DSAT and NAUI tables are significantly shorter than the older US Navy tables based on doppler ultrasound studies that were done that showed measurable bubbling in divers that were diving within the older limits. Beyond time limits, slower ascent rates reduces bubbling.

 

[Dr Deco]

Hello edylchtims:

Silent Bubbles

"Silent" is a termed used in clinical medicine to denote disease without symptoms. These include diabetes, hypertension, osteoporosis, ischemic heart disease, and chronic kidney disease. In the mid 1940s, Dr Albert Behnke, thin in the US Navy, suggested that decompression gas bubbles might be present in humans following decompression that did not result in DCS.

With the advent of Doppler ultrasonic detectors, gas bubbles were indeed detected. Since the US Navy tables had been applied for decades, it was not though that these sounds could really be bubbles. In the early 1970s, these were called by many "Doppler events" in deference to the ambiguity.

My studies with visual and ultrasound monitoring in animals were the first to demonstrate that these "events" were actual bubbles. References below.

Slow ascents, deep stops and safety stops will work to reduce the impact of "Silent bubbles."

Dr Deco :doctor:

The next class in Decompression Physiology for 2009 is April 4 and 5. This class is on Catalina Island at the USC Marine Laboratory. Contact Karl Huggins at the web site: Advanced Decompression Physiology Seminar Information

References

Powell, M. R. 1971. Decompression from pressure: monitoring by ultrasound. Union Carbide Corporation Technical Memo, Tarrytown, New York

Powell, M. R. 1972. Leg pain and gas bubbles in the rat following decompression from pressure: monitoring by ultrasound. Aerospace Med.,43, 168.

MR Powell. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring: Aerospace Med., 43, 1240-1244, 1972.

 

[edylchtims]

Thanks to all for the information. As a follow-up question- what exactly is the impact of silent bubbles? Besides fatigue, are there long term problems if there are no deep dives for a while ?

 

[DA Aquamaster]

When I started diving in 1985 we used US navy tables and a few years later PADI and others modified their US Navy based tables to incorporate reduced NDL's (for example 60' for 50 minutes rather than the time honored 60' for 60 minutes), slower ascent rates (30 fpm rather than 60 fpm) and safety stops for dives deper than 60' or within 1 increment of an NDL, all of which were based on doppler ultrasound research and efforts to reduce "silent bubbles".

In my personal experience, I used to dive with the newer tables and computers based on similar models and would do 2-4 dives per day 2-3 days in a row and then feel very flu like on Monday morning after a long diving weekend. I found that a combination of accellerated deco, deep stops and a slow ascent (10-20' per minute) from the deep stop to a 3 minute safety stop made a 100% improvement with no more fatigue or flu like symptoms.

Two weeks ago, I made 2-3 dives per day for 7 days straight nearly all of them involving mandatory decompression with stops up to 20 minutes in lenght. Doing it conservatively in terms of stops, acent rates and O2, let me do it all week with no ill effects.

I don't know what you consider "long term problems", but I have been diving nearly 25 years and plan on about 25 more so I have and will continue to adjust my deco so that I feel good afterwards. Better not to have a subclinical DCS sysptoms than to worry about the long term impact of subclinical DCS symptoms.

 

[W8less]

Question for Dr. Deco! Can silent bubbles lead to aseptic bone necrosis? I spent most of my 20's deep air wreck diving. Mostly NDL all Navy table and "safety" stops. KOW I have never been bent (to my knowledge). I am very healthy/strong for my age, but joints are prematurely shot. Total knee replacement at age 56. Any potential correlation??

 

[Riger]

As Steve said, one of the surprises of Doppler investigation of divers was that many divers have detectable bubbles after a dive, without reporting symptoms, .......

Firstly, this is a hugely interesting subject for me (does that make me a deek [Dive Geek]?), and references to any additional modern reference material are appreciated.

[-]TSandM, when you say many, do you have the data to say what sort of percentage of divers studied?[/-] Next time I will more carefully I promise. 60% is the answer... :doh2:

Also, Is it possible that these bubbles exist in the bloodstream and not in the other compartments? If so, could that be why they do not present to the subject?

I am an Air Traffic Controller, not a doctor, so please excuse any naive questions.

Best Regards

Richard

 

[Dr Deco]

The silent bubbles might produce fatigue, but they will not produce bone necrosis in recreational divers.