Search results

  1. Dr Simon Mitchell

    Question Deserved DCS hit even with deco cleared due to high exertion during the dive?

    Hello Crofrog, These are all very good questions. In relation to 'always grade 4 bubblers', we have known for some time that there some divers who consistently bubble a lot and some who don't. The short answer is that we don't know why this is. There are some hypotheses, but none proven...
  2. Dr Simon Mitchell

    NASA's solid state CO2 detector: suitable for rebreathers?

    Hello Mr V, Unfortunately this is not true. You are assuming that the only cause of CO2 problems is scrubber failure or bypass leading to CO2 inhalation. That is one way in which hypercapnia can occur, but its certainly not the only or even the most important one. It is also possible to become...
  3. Dr Simon Mitchell

    Question Deserved DCS hit even with deco cleared due to high exertion during the dive?

    Hello, Great thread. After the publication of a landmark study (arguably the most important in the last 20 years) by David Doolette and Greg Murphy less than 3 months ago, events like this should no longer surprise us, and we should definitely stop referring to 'deserved' vs 'undeserved' DCS...
  4. Dr Simon Mitchell

    Long term stored oxygen in Ali80 still safe to use?

    Hi Eric, At least some degree of caution is warranted, especially if you are dealing with a steel cylinder. I had previously heard stories of this nature and always wondered if they were apocryphal, but then this (see below) got submitted, and we published it just a three months ago...
  5. Dr Simon Mitchell

    Why doesn't oxygen cause decompression sickness?

    Hello Joebob, Yes, that's exactly what it means. Indeed, it has been done with animals breathing oxygen at 3 ATA. You can see a description of this famous old experiment here. Hello Smache, Yes, pretty much. Basically, the partial pressure of oxygen in a tissue never rises enough for oxygen...
  6. Dr Simon Mitchell

    Why doesn't oxygen cause decompression sickness?

    Hello, Lots of good comments in this thread, but this question comes closest to pointing at the complete answer to the OP's question. It is actually quite a tricky one to get one's head around, but if you're interested, here it is. To understand it, you need to understand some fundamental...
  7. Dr Simon Mitchell

    Do very deep freedives risk hyperoxia (ppO2>>1.6)?

    Hello, A great question by the OP, though the prediction calculations are slightly off. We don't have 21% oxygen in our lung alveoli during normal breathing; it is about 13%. That's because there are gases other than nitrogen and oxygen present (including CO2 and water vapor). A bit of...
  8. Dr Simon Mitchell

    Question Change sorb between dives

    Hello, If changing sorb between two dives on the same day the key elements are to: Make sure you actually change the sorb Make sure you install the canister (forgetting it entirely it has happened at least twice that I know of) Make sure you install the canister correctly (e.g. O ring and...
  9. Dr Simon Mitchell

    Anyone have experience with Eustachian tube balloon dilation?

    Hello, Diving and Hyperbaric Medicine Journal published a series of 20 divers who underwent this procedure because of ear equalizing problems. 15 improved with 10 completely cured of problems. The paper is available on pubmed central and can be downloaded for free here. As far as I am aware...
  10. Dr Simon Mitchell

    Confused on AGE; holding breath OK if lungs are near-empty?

    Hello, Diaphragmatic movement is not the only avenue for lung expansion. Upward and outward movement of the chest wall would also accommodate lung expansion. With that said, all involved structures (chest wall and diaphragm) incorporate skeletal muscle which would have to not be actively...
  11. Dr Simon Mitchell

    Confused on AGE; holding breath OK if lungs are near-empty?

    Hello, Gelirfella, while it is true that the exact mechanism by which alveolar gas enters the pulmonary circulation during pulmonary barotrauma is not well defined, there is overwhelming (essentially incontrovertible) evidence that it occurs. Specifically, in arterial gas embolism occurring in...
  12. Dr Simon Mitchell

    Question Decreasing the Breathing Reflex....Possible?

    Hello, There certainly is one way: if there is severe hypoxia oxygen certainly becomes the "dominant factor in the respiratory drive" - at least in some subjects. We are currently demonstrating this in a series of experiments in which we make subjects hypoxic, but we are not the first to have...
  13. Dr Simon Mitchell

    Question Decreasing the Breathing Reflex....Possible?

    Hello, In fact, it does. Several other commentators on this thread have correctly pointed out that the most important influence on the drive to breathe is generated by carbon dioxide levels in the arterial blood - higher CO2 = greater drive to breathe. However, if you have a higher arterial...
  14. Dr Simon Mitchell

    Is it safe to take acetaminophen or a Nsaid after diving?

    Hello, Just to put some perspective on this, the only published randomized double-blind trial of any intervention in decompression sickness (DCS) was an NSAID (as an adjunct to recompression). I have attached the paper. We showed that divers who received the NSAID had equivalent final outcomes...
  15. Dr Simon Mitchell

    Helium prices and shortage

    Hello, Yes, we came out of the Pearse on Thursday, and yes, Harry and Craig completed a 13.5-hour dive to 230m during which hydrogen was introduced below 200m as diluent in a meg rebreather. The goal is not so much to eliminate helium, but rather to eliminate the small amount of dense nitrogen...
  16. Dr Simon Mitchell

    Timeframe for diving post covid +

    Yes, of course. Entirely correct. If the risk in COVID cases were dramatically higher than baseline then you would not need such a large study to demonstrate a difference from the (low) baseline risk. Under those circumstances a randomised or cluster randomised study might even be plausible...
  17. Dr Simon Mitchell

    Timeframe for diving post covid +

    Kinoons, My main objection to your posting in this thread is your nihilistic portrayal ("failure of academic medicine" "guesswork" etc) of a diving medicine community trying to do the right thing in a difficult situation. This has been laced with an authoritative voice (you imply you are a...
  18. Dr Simon Mitchell

    Timeframe for diving post covid +

    Hello Kinoons, I have been reading your criticism of the UCSD guidelines and your confident assertions about COVID-19, diving and appropriate levels of evidence with increasing concern. In the context of a discussion about return to diving this statement is incorrect. SARS-CoV-2 can produce a...
  19. Dr Simon Mitchell

    DOWN CURRENTS -Any with true real-life experience?

    Hello, Arguably one of the most spectacular down-current accidents ever - a triple fatality when 7 scuba air divers were sucked down from 30' to ~300'. See published description attached here, also downloadable at...
  20. Dr Simon Mitchell

    Timeframe for diving post covid +

    Hello, Yes we do. There is absolutely no doubt about it. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6704005/pdf/DHMJ-49-141.pdf There are also multiple published cases of pulmonary barotrauma and arterial gas embolism just by ascending to altitude in an aircraft if you have a gas trapping...
Back
Top Bottom