Excessive MicroBubbles

[SM Diver]

I made four shallow dives on Sunday, and didn't realize until later that I dove through three alarms on that day. I found out when I uploaded my COBRA dives into Dive Manager, and the alarms showed up as the "Diver Alert Symbol" on the graph.

None of the dives were past 22ft, so after each dive I came up and checked my computer, stayed out of the water for about 15-20 minutes, and dove again. Obviuosly, at those depths, even on quick, repetitive dives, my no deco time was off the chart, and greater than my air supply.

I did some reading on this small "Diver Alert Symbol" used by Suunto, and it is an alarm for excessive microbubbles. All dives but my first had that symbol.

That seems very conservative, to have to wait more than 15 minutes when I am going down 21 feet, even doing four dives in a day. Is there a generally accepted minimim surface interval for even very shallow dives?

 

[Dr Deco]

Dear tampascott:

Surface Interval

To my knowledge, there is not a prescribed minimum surface interval other than what is indicated in the dive tables. In the case of very shallow dives, this would certainly exceed the air supply for anything but a surface–supplied diver. While bubbles have been monitored and found in shallow dives, this was for a saturation dive in a habitat. The record for precordial bubbles is about 18 feet. {Eckenhoff RG, et al. Direct ascent from shallow air saturation exposures. Undersea Biomed Res 1986 Sep; 13(3): 305-16; Eckenhoff RG, et al. Human dose-response relationship for decompression and endogenous bubble formation. J Appl Physiol 1990 Sep; 69(3): 914-8}

Microbubble Warning Signal

Why this would appear on your computer with this exposure is a mystery to me. The truth is, why it is there at all on any computer, I do not know (on the basis of physiology). Here are some comments:

• The presence of microbubbles can only be told by direct monitoring (with an ultrasound device, for example);
• If microbubbles were known to be present before hand, and the table designer believed that it made a difference, the decompression limits should be modified; and
• We have checked on this aspect (NASA study), and sufficient microbubbles are not present in actual human decompressions to modify the gas exchange characteristics in the lungs.

I believe that manufacturers like to add things because they are thought to be of value, but the physiology behind this is dubious (in my 30+ years of research experience).

Dr Deco :doctor:

 

[rcohn]

I've run into the same thing. You can see my previous post and the "expert" advice I received here:http://www.scubaboard.com/showthread.php?s=&postid=117432&highlight=mosquito#post117432

Ralph

 

[Zept]

Not sure if it applies in your case, but in my experience, if you trigger the ascent alarm during the dive, Suunto computers will often (possibly always) encourage you to 1) do a safety stop and/or 2) extend your surface interval.

If the alarms you're seeing on the graph are ascent alarms, that could explain the appearance of the 'diver attention' symbol during your surface intervals.

Zept

 

[Genesis]

I have a Vyper and know EXACTLY how you did this - 'cause I've done it too

Basically, what happened is that you violated the ascent rules at some point in your profile. This is VERY EASY to do on a very shallow dive (as you were doing), since there isn't a lot of time for the computer to average things out over, and particularly if you grab the console, raising it 2-3' as you start up - you violate the ascent rate yet you've hardly moved! With no time for things to average out and calm down, you get a STOP that you never even see. I've gotten this a couple of times diving the jetties around here - its a 40' profile, but when you swim back to the boat before surfacing you're only in about 15-20' of water, and simply going from prone (swimming) to head-up can trigger the alarm on my Vytek when the water is that shallow if I'm looking at the computer at the time (since it then has a fairly serious "swing radius" in terms of depth.)

(I've managed to get this once while swimming up the side of a wreck about 10' high and dropping over the other side exactly the same way - I looked at the console on the way up, which added to the "ascent rate" and gave me a momentary warning which I never knew happened until I got to the surface!)

If you do come to the surface with one of these ascent violations in the computer for the current dive, when the dive times out (5 minutes after you surface) the attention symbol (A "!" in a triangle on the left side of the display) comes on.

(The other way to make it show up is to blow off the safety stop. That'll turn it on too, but I don't do that....)

After a "suitable" surface interval, it will shut that off. If you go in the water and dive again with it still lit, then you get that warning for the entire (next) repetitive dive, and the computer penalizes your available bottom time.

Typically, it takes at least an hour for the attention symbol to disappear. You can go into the PLAN mode and add surface interval to the current amount to figure out if the symbol will be on or not when you intend to start the next dive; it will come on in the plan mode if your intended surface interval will be insufficient for it to go away.

If you have the Dive Manager and go into the graph for the dive, you'll see where the STOP came on. It could have been anywhere and only for a second or so - if it happens, you get the attention symbol - period. Depth of the dive is irrelavent. You can also see it if you go back through the logbook (it will "reply" the dive for you) but you have to look sharp, because if it was a transient the "STOP" will flash only momentarily when that particular recorded segment comes up.

The lesson here is to ascend SLOWLY, particularly during the last 20' or so. That's a good idea anyway for reasons we all know - the Suuntos reinforce the rule by penalizing you if you don't!

The Suuntos are VERY conservative on microbubble formation - which at least from my point of view is a GOOD thing, since microbubbles seem to be implicated in an awful lot of "undeserved" DCS hits.

 

[SM Diver]

Guys, the rapid ascent issue is one of the first things I looked into. I use every ascent as a practice session, even when coming up from only 20 ft. I like to practice suspending myself for a few seconds at every one foot interval, just to practice buoyancy control, and conservative diving skills.

In looking at the graph, there is no "slow warnings" on any dive (which is a seperate symbol than the diver alert). In fact, I never even got the first "bar", indicating rate of ascent. Furthermore, I never got even a recommended safety stop, which is very rare for a Suunto computer.

I dive redundant computers, with COBRA and VYPER. Presumably, both of the computers run off the same mathematical models. There were both set to the default diver profile. I only got one micro alarm from VYPER, three from COBRA.

When I went back and reviewed the manual, Suunto gives very little attention to this diver alert, and what it even means. There's a small reference to microbubbles, but my guess is that it's so theoretical, that they can't explain.

My final guess would be that Suunto ignores the depth altogether, and gives you a microbubble alert if your surface interval is less than "x" minutes. I know there are a lot of Suunto users, so I'll see if I can get more on this from the manufacturer.

 

[Genesis]

is not just conditioned on short SIs. I've done that before and not gotten it on shallow dives....

 

[SM Diver]

Q: Sometimes a warning triangle appears in my dive computer that means I should not dive right now. Does it appear because the medium tissues are still saturated?

A: The warning triangle indicates "extend surface triangle". This is prompted when you are subject to excessible amount of micro bubbles and does not necessarily relate to tissue saturation levels.

That's from their website. Until Suunto explains this better, there will continue to be confusion.

rcohn, just saw your thread, and it looks like we had identical issues.

Dr. Deco: Thanks for your input on that.

 

[Dr Deco]

Dear Scott:

Tissue Bubbles and Gas Exchange

Having read the small piece in the SUUNTO FAQ section that was given, I see what the algorithm designers have in mind. They are saying that the perfusion (= capillary blood flow) through a tissue will be reduced by gas bubbles in the capillary system and hinder the wash out of dissolved nitrogen from that tissue volume. This is not reflected in normal algorithms because the half times are “state independent” (= not modified by the condition of the diver).

In the ATTACHMENT we see a slide that I have used for about the last fifteen years from my Decompression Physiology class. (In fact, one class actually made this into a tee shirt and gave it to me at the end of class. They had seen it too much.)

“Before the first dive” illustrates the condition with all capillaries patent. The on gassing during the dive will be normal. This is the condition or state normally expected in the deco algorithms.

“During the first surface interval” illustrates that a free gas phase has formed in some of the capillaries. This has blocked the blood from flowing and dissolved nitrogen washout is hindered. This is what SUUNTO means (I believe) when they say that something has occurred in the tissue that is not reflected in the customary halftimes.

After the second dive” shows that the microbubble has regrown even larger. This is because we had essentially an “injection” of nitrogen (from the capillary bubble) into the tissue, and now, during the subsequent depress, we have a “giant micronucleus” (an oxymoron, somewhat analogous to jumbo shrimp).

Dr Deco :doctor:

 

[rcohn]

Since it has been suggested that the problem is caused by ascent rate errors I thought try out the attachment thing and post my actual dive profiles, direct from Suunto Dive Manager that resulted in a diver attention symbol violation after a 1 hour and 3 minute surface interval. The only ascent rate violation occured on the first dive of the series when surfacing to assist a student. This was over 25 hours before the start of the fifth dive. Also the dive log shows a new dive series on Sunday, indicating the computer had desaturated (no fly interval completed) prior to the start of dive 4.

Diver statisitics were:
Saturday:
Dive 1 Surface int. >99 hr, Max depth 16 ft, Ave depth 14 ft, duration 1min:20s
Dive 2 Surface int. 8 min, Max depth 13 ft, Ave depth 10 ft, duration 10min:40s
Dive 3 Surface int. 1hr:27min, Max depth 25 ft, Ave depth 15 ft, duration 27min:0s

Sunday:
Dive 4 Surface int. 21hr:37min, Max depth 31 ft, Ave depth 20 ft, duration 19min:20s
Dive 5 Surface int. 1hr:3min, Max depth 41 ft, Ave depth 23 ft, duration 25min:0s

Ralph