From: story@sgi.com (David (Duis) Story)
Newsgroups: rec.scuba
Subject: Re: ?diuretics and diving
Date: 9 Sep 92 19:34:13 GMT
Organization: Silicon Graphics, Inc.

In article <1992Sep9.012557.21801@mailer.cc.fsu.edu> mayne@cs.fsu.edu writes:
>In article <pk0rt8k@twilight.wpd.sgi.com> story@sgi.com (David (Duis) Story) writes:
>>
>>The reduction in tiredness after using Enriched Air is believed to be
>>due to the reduction in asymptomatic DCS, not increased O2 (which your
>>body can't use anyways.)
>
>If it is true that using Enriched Air (aka nitrox) is reducing
>"asymptomatic DCS" and this explains why some people feel better
>after a dive using nitrox than they would have after the same
>dive on air, I question whether the DCS is, strictly speaking,
>"asymptomatic." Is tiredness just an unrecognized symptom?

Yes.  It's not really "asymptomatic", if you recognize the symptoms.
But folks are really really bad at recognizing the symptoms -- or is
it admitting that they are DCS symptoms?  As proof, witness the
incredibly long average delay between the last dive and treatment for
DCS, as reported by DAN.

>It is truely scary to think that we are routinely suffering
>unrecognized DCS like that.

Yup.  Makes safety margins a big deal.  Also makes me wonder about the
1/2 of the day boat passengers who are sleeping on board instead of
making that last dive of the day....

>Are there long term consequences to such "asymptomatic" DCS?

Commercial divers have shown long-term consequences of routine extreme
exposures.  No such database exists for sport divers, though a few
post-mortem studies of folks who were bent once or more showed
scarring in key areas, believed to be the result of the bends.

>This would seem to be an extremely strong argument for nitrox.
>But why wouldn't just backing off a couple of stops on the tables
>give the same benefit, if the well accepted theory of equivalent
>air depths is correct? Of course we can't back off a couple of
>stops on no-decompression dives.

Sure, backing off is a good idea.  And you CAN actually back off a
couple of stops on a no-STOP dive by making a "safety" stop.

Remember, EVERY dive is a decompression dive!  You are decompressing
when you surface, aren't you?  You were supersaturated, weren't you?

>At what partial pressure of O_2 is it true that your body can't
>benefit from more? 

One way to define this might be to consider this the pressure of O2 at
which your hemoglobin is 100% saturated, which is really low, about
100mmHg: approximately the *normal atmospheric partial pressure of 02.*

>Obviously it is higher than .21 ATA, or we
>wouldn't use pure oxygen for first aid (except possibly for
>DCS hits to wash out nitrogen). 

I think that the mechanism you mentioned in an earlier post, the
diffusion of O2 past blockages, applies to normal injuries as well --
often your circulation is greatly compromised from simply adrenaline
rushes, excessive bleeding, or shock and corresponding blood pooling,
and O2 may be cut off to areas that need it.

>>Did you know that you lose heat as quickly in 80F water
>>as you do in 42F air?
>
>Thanks for reminding me to thank Oztotl for 70F spring water.

Yes, but Oztotl withheld giant kelp from your diving diet!  :(

>But what does this 80F to 42F figure mean? Does it assume you are
>naked, with no wind or current in either case?

Swimtrunks, no wind or current.  Yes.  Still pretty amazing, eh?  From
_Diving Medicine_, 1990, by Bove and (RIP) Davis.

Cheers,

Dave Story@bent.wpd.sgi.com           NAUI AI Z9588, PADI DM 43922, EMT
    Spearfishing on SCUBA is like hunting bears from a helicopter.