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dive computers with Doppler ultrasond bubble monitors

Discussion in 'Ask Dr. Decompression' started by rcohn, Jan 12, 2001.

  1. rcohn

    rcohn Manta Ray

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    Dr. Deco,

    I was curious to hear what comments you might have on the following article. From your past posts I think I can guess what they might be, lets see if I'm right.

    Ralph


    From: http://www.cnn.com/2001/HEALTH/01/10/health.bends.reut/index.html

     
  2. Dr Deco

    Dr Deco Medical Moderator Staff Member

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    A device such as the one described is doubtlessly a Doppler bubble detector, though where the ultrasound transducer would be placed is not derivable from the description.

    In my opinion, these devices would only be of practical value for determining that repet surface intervals should be lengthened. That would be a practical addition, however.

    I would be curious to follow this idea, as some aspects of this have been discussed in this FORUM.

    I am not exactly certain how much I would want to say publically about a medical and commercial device such as this at this juncture in time.
     
  3. BillP

    BillP Senior Member

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    Another version of the news release is available on the BBC's website at http://news.bbc.co.uk/hi/english/health/newsid_1110000/1110678.stm .

    That story calls it "a wrist mounted ultrasound device" and says that it "uses ultrasound to work out how many gas bubbles are in the blood vessels at the wrist". I think that you're probably right that it's a doppler. The device is designed to be worn at depth while diving and on surface intervals.

    Dr. Deco, I can see where a doppler could be of some utility on the surface to see if you might want to lengthen your surface interval, but would it be of any significant help to a recreational diver to have a waterproof doppler at depth? Do not most ultrasonically detectable bubbles in non-saturation divers form after ascent? Would a device that detects bubbles in the circulation at the wrist help you detect that you're developing "Type I DCS" from bubbles in the knee? Even if bubbles were detected at depth, would not the typical recreational diver's gas supply be too limited to extend their stop at the end of the dive to make much difference? If you wanted to follow your bubble status would you be just as well served by having a surface doppler (like has been available for decades) to check yourself on the surface interval?

    TIA,

    Bill
     
  4. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
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    Bill:
    The story is beginning to unfold:
    • It appears to be a Doppler flowmeter at the wrist. This would indeed not give information on the locus of bubble formation/growth in the body as a whole. That aspect of the bubble-detection theory has a flaw.
    • For the recreational diver (always unsaturated), the gas bubble appearance in the venous return at the surface. It is possible that in some cases involving decompression (and more of this is occurring in rec diving today), bubble formation/growth with movement into the venous return, could occur at the 10-foot stop. This would then give an indication that the “stay time” should be extended at ten feet.
    • It is my understanding tht the individuals developing this deco device are performing dives for commercial purposes (e.g., filming), and are not recreational SCUBA divers.
    • Certainly, if bubbles appeared on the surface in the venous return, one might want to decide if the surface interval should be extended. This could well depend on the Bubble Grade (= amount of bubbles). Precordial gas bubbles (Spencer Grade 0-II) were detected in the laboratory and sea trails of the PADI RDP dives and thus were not totally eliminated or unexpected.
    • One problem of these devices lies in the testing of them. Simple test programs virtually never involve cross-over trails of competing conditions. It is seldom acknowledged that PADI was the only organization to pay for the testing of tables. Virtually all computers on the market today simply insert theoretical models with little data to back them up, unless they have a simple Haldanian algorithm. Testing is expensive!
    • There exists a fairly high degree of variability among individuals in their response to decompression and their propensity to gas bubbles formation. That fact that some divers (or aviators) will acquire decompression sickness in the absence of any venous return bubbles while the incidence rate for those with a Spencer Grade four is about 50% illustrates that the correspondence is not extremely good. All good research groups in the world today labor under the principle that few to no bubbles in the group as a whole is the harbinger for good deco procedures. The use of a device for real-time deco is not envisioned in the near future. This is even true at NASA where the consequences of a bad deco procedure could be very costly.
    • It is true that a device such as Doppler bubble detectors can be purchased for surface use for three thousand dollars (one is based on a NASA design) that would give the necessary information. The signal does require interpretation.
    • People have discussed the desirability of using Doppler bubble detection in the community as a whole since the mid 1970s. There has never been any type of agreement on the desirability of this practice.
    [sp]I am attempting to be candid in my response, although one must recognize that I am not at complete liberty to say all. Partly, this will be a consequence of not knowing all information “except what I read in the newspapers.” Partly, this is the fact that much of the day-to-day workings of NASA are not for public disclosure on an hour-by-hour basis. We all can recognize that would not be possible.
    [sp] Let us see how this plays out in the future......

    ______________
    [sp]Dr Deco
     
  5. John Reinertson

    John Reinertson Barracuda

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    I'm not in Dr Deco's league, but have some background in Doppler research and engineering before I settled into family practice.
    Fortunately, I'm not employed by any one connected with the industry, so I can present my SWAG's freely. (scientific wild-a__ guesses)
    No bubbles indicates decreased deco risk. Once the bubbles are present, however, it would be necessary to recompress to stop bubble growth and slow formation of new bubbles or possibly switch to 100% Oxygen to affect risk by much.
    If you're bubbling at 15 feet, shrinking the bubbles by recompression would require going substantially deeper. There are a number of technical reasons why in-water recompression for DCS is not real feasible. (Look at a Navy Treatment Table 6 and try to complete that underwater!)
    The same thing would apply to shrinking bubbles by slowing ascent, I would think. The most effective treatment for DCS is getting out of the water, on to 100 pct Oxygen, and get to the nearest chamber.
    Should asymptomatic bubbling be treated with 100 pct Oxygen? There's no research, but if i knew I was bubbling after a dive and had Oxygen available, I'd probably consider it myself. Would such a computer be useful to gather data about asymptomatic bubbling? The best place to find bubbles is in the largest veins or the right side of the heart. I wouldn't be real excited about the likelihood of accurate data from the vessels at the wrist, at least not without some convincing studies. If it involves a chest probe for the doppler device and I were a commercial or navy diver doing saturation or aggressive profiles, I might want to detect and treat silent bubbling at least until we get data that shows it can be safely ignored, but I'd want to treat it with Oxygen at the surface and possibly a chamber ride if the bubbling were severe.
    Until we get clearer data, treat bubbles as something to blow in the water, but not get in your blood. Dive safely. I'd rather shorten one dive than my life.
    John Reinertson
     
  6. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
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    The latest “traffic” on this issue from Mr. Forbes seems to indicate that it is a bit of dreaming on the part of the magazine editors. :bonk:

    The comment was made by him that they were looking at improved methods of discriminating gas bubble signals in the blood. This information could be applied to the improvement of decompression techniques and equipment (such as deco meters) in the future. He states that the editors apparently pasted together the idea of the bubble detector and the wrist-worn deco meter and gathered that the devices were an single, physical reality. :wink:

    What has been written in the past couple of days in this FORUM is still correct regard decompression theory. Yes, it would be difficult to develop a real-time device. I would certainly like to be a part of the team trying to do it, however!!! :idea:

    Possibly a merciful God will allow me the opportunity one day.....
    ________________________
    Michael R. Powell, PhD Dr Deco

     
  7. rcohn

    rcohn Manta Ray

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    Dr Deco,

    What alternative sensing techniques have been tried? From what you're saying Doppler bubble monitoring in the blood doesn't sound too useful. It seems to be relatively easy to measure, but the correlations with DCS appear to be too low for a useful device.

    I'm guessing that monitoring bubble development in the tissues (possibly the fat) might be more useful. Have the researchers investigated things like ultrasonic or optical attenuation and scattering; spectroscopic changes; conductivity; etc. to try to detect increases in the free phase? Clearly without the Doppler component it is a much more difficult task to identify signal changes due to bubbles. I seem to remember a Navy SBIR topic from around 8 or 9 years ago for a DCS monitor, obviously nothing seems to have come of that.

    Thanks for the information.

    Ralph
     
  8. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
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    The search for a good device to detect a gas phase has been a long one. It reaches back to pre WW II when x-rays were tried. This only works for larger pockets of gas.

    There have been several attempts over the years to employ ultrasound. I joined Ocean Systems in 1969, and U/S was one of my first projects (a though-transmission system).

    I can describe what systems have been tried, but the result is always the same, viz, movement artifacts always produce a change in the signal that exceeds that from bubbles. The only system to date where motion artifacts can be sufficient suppressed is with the Doppler flowmeter.
    • Through transmission systems where U/S is sent across tissue from one transducer to another.
    • A harmonic approach where the bubble is made to oscillate in the U/S field and the scattering of the ultrasound beam increases.
    • A double frequency, harmonic approach where the bubbles are “pumped” with a high frequency U/S and the movement of the bubble surface is detected with another U/S beam that is scattered.
    • An electrical method whereby the impedance of the tissue increases when bubbles (resistances) are in the circuit.
    • Acoustic holography was tried where U/S and laser beams were made to interact to produce an image of tissue and bubbles.
    • Direct observation by the use of small microscopes that can be inserted into tissue.
    • Various biochemical markers have been investigated, but success has been had only in very severe decompressions in animals.
    One advantage of Doppler systems is that you can have a final focus for the whole body, namely, the right heart. All other systems would require that every tissue is interrogated individually, a very difficult task in a moving subject.
     
  9. Michael White

    Michael White Guest

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    This addition to the thread may get technical and therefore may be better taken off-line, but I have some questions.

    There is a continuing solicitation from the US Navy for non-invasive methods for prediction and detection of DCS. Being a research scientist at a company which subsists on technological challenges like this one I am interested in this subject. However, some key information eludes me which someone, or perhaps Dr. Deco himself may elucidate for me:

    Do you know of any studies which include the bubble size, or population of bubble sizes in the blood stream vs pressure and time? In particular I am interested in bubbles smaller than are typically considered detectable by acoustic Doppler.

    Similarly, the connection between DCS and microbubbles is not obvious to me. Certainly there is some contribution of bubbles growing as gas precipitates out of the blood and some contribution from the coelescence of many small bubbles at restrictions in the blood stream, perhaps due to flow shear at joints etc.

    Do microbubbles appear throughout the bloodstream during decompression? Are these bubbles an indicator of DCS or are other factors required to create the larger bubbles which lead to DCS symptoms? If such bubbles are detected in small vessels away from the heart (in the eye for example)is there a correspondence to later formation of larger bubbles in the joints or near the heart? And if such bubbles are detected during decompression underwater, is there the possibility of reversal of the gas precipitation or is it just to the surface and to the nearest treatment center?

    Somewhat coincidentally I am taking a diving certification course now, and I consider this a fascinating problem. My background is laser remote sensing, not medicine or anatomy, so I have a lot to catch up on.

    Thanks in advance for any information you can offer.

    Michael White, Ph.D.
    Research Scientist
    Physical Sciences Inc.
     
  10. Green_Manelishi

    Green_Manelishi Solo Diver

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    nooooooooooo, don't take it off-line. if it is technical
    so be it.

     

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