Medical Issues of Diving at Altitude

[Duke Dive Medicine]

Here's what I am wondering about. I have seen enough people go to the chamber in Cozumel due to sloppy profiles, skipping deco stops and too many days of repetitive diving that my question is from the emergency responder point of view. If they dive up here at at altitude (I just found out we have a lake at 7,500 feet with a max depth of 350ft.) Are they in any WORSE trouble than the same guy who is sloppy at sea level? My gut says that even if the deco tables on their computer takes the altitude into consideration...when they surface...they aren't at sea level and most of them are going to stay at altitude. I wasn't asking what the computer adjusts for... What I am wondering is, if things go south...is the fact that you don't come out of the water at sea level a factor that makes things significantly worse or does it not matter?

Hi Cougar, sorry it took so long to respond to this, very busy week with multiple inpatient treatments here. It sounds like what you're asking is whether DCS symptoms present more quickly and/or more seriously after an altitude dive than after a dive at sea level. To really give a solid answer to that you'd have to have a sizable number of DCS cases that fit those circumstances, and I'm not sure that there are. From a physiologic perspective, it would depend in part on how long the individual had been at altitude. The Navy diving manual actually assigns repetitive group designations based on the altitude and the time spent there. The higher the initial ascent, the higher the residual nitrogen level, so it follows that someone who makes a significant ascent to altitude then dives right after would be at a theoretically higher risk of DCS. That's hard to translate to reality, though. My best answer would be to treat the symptoms as they occur and ensure that you have a good emergency action plan for diving injuries. I'm happy to work with you on the specifics of that if you'd like, so PM me if I can be of any assistance.

Best regards,
DDM

Actually i was wondering about that too.

If you finish a dive at 3000ft altitude and the dive had max depth 65 ft is it safe to return after the dive at sea level or it is dengerous?

Lambroskol,

It's quite safe to return to sea level after an altitude dive because you're increasing the ambient pressure and so reducing the pressure gradient between the dissolved gas in the tissues and the ambient air.

Best regards,
DDM

 

[Agility]

It's quite safe to return to sea level after an altitude dive because you're increasing the ambient pressure and so reducing the pressure gradient between the dissolved gas in the tissues and the ambient air.

You only have to make sure you do not go uphill first to get over a pass (as is often necessary in the alps) before going down.

 

[Duke Dive Medicine]

True that. Good point.

 

[theduckguru]

Suunto suggests the diver should allow a 3 hour interval at altitude to off gas nitrogen before diving.

 

[TheAvatar]

Last time I checked, which was a while ago, none of the computers were taking nitrogen preload from pre-dive-ascent from lower altitude. I didn't see any that gave a time-to-safe ascent either, usually just flying timers. This information is necessary, particularly if the way home is over a pass. In these situations, tables are very useful.

Suunto suggests the diver should allow a 3 hour interval at altitude to off gas nitrogen before diving.

The tables presume that you have fully saturated all tissue compartments to the ambient ppN2 at the lower altitude... while the difference is not huge, even going from 5,000ft to 9,300ft, 3 hours seems a bit short to write off the preload with no regard the actual change in altitude. The Navy recommends 12 hours. I dunno what the Sunnto would give on the OP's example of a 68ft dive time 9000something dive site coming from 5000ft, but if you use the tables it drops the max bottom time from 20min to 7min, which is quite a large difference.

Then say you do another dive, and you wanted to drive home over a 11,500ft pass, you'd need to look at the tables which could easily tell you that you ought to wait 5 or 6 hours before you drive over that pass.

Oh, one last thing, don't forget you adjust your actual safety stop depths shallower for altitude (there is a table for that too).