flying after diving

[HammerNoMore]

rmediver2002 once bubbled...
I know DAN is working on this issue for the Navy right now, and from what I heard the delay before flying time will be decreasing not increasing.

Yes, they are working on it and being very vague about the results so far. They have already decreased their suggestion to 18 hours from 24 after multiple days, but I sort of interpret their vage statement as:

"We can't find prove that there is any reason to wait 18 hours, we just feel it is better to be safe than sorry."

It is clear that once bubbles have formed, altitude will do nothing but make them bigger, but I've never really seen any proof that flying causes DCI.

Looking at it logically, I can see that if you were close to DCI and jumped immediatly out of the water and on to a plane, the extra decompression could cause problems. But in reality, it would be be extremely unlikely to be on a plane within an hour of your last dive.

Others have pointed out that even without a pressurized cabin the pressure change when flying is equivalent to the last 15 feet in the water column. So FAD would be equivalent to takeing a 1+ hour safety stop and then doing a slow ascent.

One real concern is the affect of a sudden cabin depressurization. I think, however, you have a much better chance of getting killed on the way to the airport, especially at most Carribean destinations.

Now before Charlie, Big Jet Driver, and Dr. Deco get all worked up about this. I am not recomending or using the "wet hair" approach. I too believe in better safe than sorry. I think the facts need to be found out and DAN is working on it, though I don't really expect to see any recomendations from them that don't have a CYA factor built in.

This issue smaks of the whole diving while pregnant thing. I.E. We just don't know what will happen so were gonna say don't do it.

James

 

[Saturation]

James Goddard once bubbled...
I'm curious. Can anyone point to any statistics/studies on actual DCI rates caused by FAD? Not people who had DCI on the ground that got worse after flying but people who actually developed symptoms of DCI in the air...

The stats are legion, the quality of the data, variable. A recent analysis of most existing data summarized as:

The relative risk of decompression sickness during and after air travel following diving.

Freiberger JJ, Denoble PJ, Pieper CF, Uguccioni DM, Pollock NW, Vann RD.

Diver's Alert Network, and Duke University Medical Center, Center for Hyperbaric Medicine and Environmental Physiology, Department of Anesthesiology, Durham, NC 27710, USA. jfreiberger@dan.duke.edu


http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=12398259&dopt=Abstract

 

[Saturation]

James Goddard once bubbled...

It is clear that once bubbles have formed, altitude will do nothing but make them bigger, but I've never really seen any proof that flying causes DCI.
Now before Charlie, Big Jet Driver, and Dr. Deco get all worked up about this. I am not recomending or using the "wet hair" approach. I too believe in better safe than sorry. I think the facts need to be found out and DAN is working on it, though I don't really expect to see any recomendations from them that don't have a CYA factor built in.
James

Hi All:

The issue with FAD is a human body is at inert gas saturation at ASL=0 or 1 ATA, and flying to a cabin pressure of 0.6 ATA puts a RISK of DCI even without diving. This is well known for military pilots trained in hypobaric exposures. The risk for DCI can be reduced by prebreathing 02 before flight but it doesn't eliminate it.

With diving, tissue inert gases are higher than at 1 ATA, not to mention the potential for micronuclei of sufficient size agitated by the dive. As Dr Freiberger mentions, the risk is not just the FAD time, but also the depth and time spent at depth for the dives prior to flight.

Dr. Frieberger puts the issue in perspective as 'relative risk', in the study I posted he calculates an 8x increase for someone flying within 20h period compared to someone flying after 28h.

Note, these are for recreational dives without 02 decompression or mandatory stops.

 

[BigJetDriver]

James Goddard once bubbled...
Now before Charlie, Big Jet Driver, and Dr. Deco get all worked up about this. I am not recomending or using the "wet hair" approach. I too believe in better safe than sorry. I think the facts need to be found out and DAN is working on it, though I don't really expect to see any recomendations from them that don't have a CYA factor built in. James [/B]

James,

Thanks for the mention! I'm glad you're not part of the "wet hair" school of thought. We'd like to have you back on board for many other trips to great dive destinations!

 

[Dr Deco]

Dear SCUBA SOURCE Readers:

Flying and DCS

At NASA and at the Air Force laboratory at Brooks AFB, there is a considerable amount of information on DCS that is encountered during exposure to altitude without previous exposure to increased pressures. These experiments are rather straightforward to conduct.

If, however, you add a prior exposure to pressure, the combinations begin to mount. We could take exposure to the NDLs and then excursion to 8,000 ft (cabin altitude) following a nine-hour surface interval. From 40 to 130 feet (by tens) that is 10 sets. Lets us put 20 subjects in each. We will then move on to a surface interval of 12 hours; that is 10 more sets. We progress to 15 and 18 and 21 hours as the surface interval. Some of these might be removed as a pattern is [possibly] becoming apparent. That very large series might be performed with all subjects at relative rest between the pressure exposure and the “flight.” [I do not know what is involved in the DAN test program so this is simply an illustration of what I might consider a complete test.]

We might then repeat much of the series, again abbreviated because some pattern is probably evident, with subjects who perform some type of simulated activity suggestive of individuals preparing for a trip. This might include some lifting following the dive. Some walking every 30 minutes, and, prior to the “flight,” exercise suggestive of hauling luggage to the airport and boarding.

Cost

I have no idea what are the costs of the chamber exposures at DAN so I will leave that out. I do know that for the longer surface intervals, it will be necessary to provide food and overnight lodging for the participants. I know from my days when I was the head of the DSAT (PADI) Recreational Dive Tables, that this round-the-clock supervision was expensive. For medical reasons, all participants were continually observed, taken to and from housing, and to and from meals. This is a medical requirement.

It does not take a CPA to see that this requires time and considerable money to perform in a rigorous fashion. Even as extensive as this would be, it would include only 20 test subjects at each exposure – a “drop in the bucket” in terms of a real week of diving around the world. If we factor in the possibility of lawsuits, it is clear that organizations will be conservative. Yes, they will add a CYA factor.

Dr Deco :doctor:

 

[HammerNoMore]

Saturation once bubbled...

Dr. Frieberger puts the issue in perspective as 'relative risk', in the study I posted he calculates an 8x increase for someone flying within 20h period compared to someone flying after 28h.

Can you explain these figures a bit more? I see where you come up with your 8x increase from:

Relative to flying > 28 h after diving, the odds of DCS (95% CI) were: 1.02 (0.61, 1.7) 24-28 h; 1.84 (1.0, 3.3) 20-24 h; and 8.5 (3.85, 18.9) < 20 h.

.

What I am not clear on is what do the numbers (1.02, 1.84 and 8.5) represent? Surely this is not a 1.02% chance of developing DCS by flying 28 hours after diving.

 

[HammerNoMore]

Dr Deco once bubbled...
At NASA and at the Air Force laboratory at Brooks AFB, there is a considerable amount of information on DCS that is encountered during exposure to altitude without previous exposure to increased pressures. These experiments are rather straightforward to conduct.

I guess I should have been more clear. I understand that you can get DCI from any drop in pressure. My questions lend more to the likelyhood of such occurances.

[I do not know what is involved in the DAN test program so this is simply an illustration of what I might consider a complete test.]

If we factor in the possibility of lawsuits, it is clear that organizations will be conservative. Yes, they will add a CYA factor.

I do hope that we get a complete test from DAN am optimistic about it. The question of CYA will hopefully be represented simply in the the recomendations, and the data will be presented so we can really begin to have fun picking it apart

 

[Saturation]

James Goddard once bubbled...

Can you explain these figures a bit more? I see where you come up with your 8x increase from:

What I am not clear on is what do the numbers (1.02, 1.84 and 8.5) represent? Surely this is not a 1.02% chance of developing DCS by flying 28 hours after diving.

My pleasure. Relative risk refers to risk compared to a baseline, in this case being a "28h FAD" risk for DCI. Whatever the real risk is for DCI maybe unknown or uncertain, but whatever the value lets make it the baseline and call it 1.0. Thus, all risk is then referenced to this value. The "1.02" exists from the way the statistician chose to combine the data from various studies.

Risk is not static, in actual calculations the risk is a continuous value [1,2,3,4,5,6, etc.,] the shorter the interval between flying and diving.

"Relative to a baseline" must be interpreted cautiously. Without knowing the actual risk for diving at >28h it may give an alarming figure, it could be very small and say as example its zero, in which case 8 x 0 = 0, and is moot, isn't it?

 

[HammerNoMore]

Saturation once bubbled...

My pleasure. Relative risk refers to risk compared to a baseline, in this case being a "28h FAD" risk for DCI.

Crystal clear. Thanks!

Without knowing the actual risk for diving at >28h it may give an alarming figure, it could be very small and say as example its zero, in which case 8 x 0 = 0, and is moot, isn't it?

Yes, this is the important part of the puzzle that is missing.

Another study from the same site mentioned looking at a little over 1000 cases of scuba related DCI. This study showed that in 5.6% of the cases the symptoms first presented during or after flight. While it might seem sigificant, there is no data on how many of these people would have developed symptoms had they elected not to fly.

The other missing factor is, as you pointed out, what percentage of total dives do these 1000 incidents represent.

Again, I hope to see some more useful data come out of the current DAN study. Untill then we just have to guess...

James

 

[sealkie]

24 hours

I see no point in pushing the limits

I don`t want DCS ... thank you !


the 12 / 24 hour rules are based on table dives whihc are generally much more conservative than computer dives

I have had my computer showing 28 hours no fly on a week long intense trip