From: Bill Bowden <BBOWDEN@co*.vo*.fl*.us*>
To: dlv@ga*.ne* <dlv@ga*.ne*>
Date: Tuesday, February 24, 1998 11:20 AM




>Dan,
>
>I appreciate you and others keeping this information coming.  Would you
>post the medical requirments for deep trimix diving?  I'm especially
>interested in any testing (esp. pulmonary function) that should be done
>either before diving, or on an annual basis.  Could you please explain the
>relationship of weight to gas transfer?  Thanks.
>
>Bill

From a physiological standpoint, there are enormous differences
which would occur between an overweight , sedentary diver, and a worldclass
cross country skier ( elite level Cross country skiers are known for having
the highest VO2 max levels among sports requiring aerobic power). While the
differences could be dramatic here, in the real world, there are people who
dive, who represent shifts from the average model, in each direction. As a
diver gets closer to either extreme, the relevance of the issue becomes much
greater.
In this example, our Olympic Cross county skier / diver, has a HUGE VO2 Max.
This means that he can process  over twice as much oxygen per kilo of
bodyweight, than the "average diver", which the tables are based on.  What
this also means, is that all gas exchanges can  be drastically increased in
this athlete's body, if his heart and breathing rate get elevated by
exertion. If he is exerting, in addition to much more oxygen uptake....CO2
will exit much faster ( this is good); Nitrogen will enter much faster
nitrogen enters the blood by gradient, at the alveoli....if this gradient
exposes twice as much blood , because this man can move twice as much blood
through his body and lungs as can Joe Public , more nitrogen will be
ingassed---a lot more. This can be bad---BUT, the skier  can also offgass
much faster at a deco stop ...so if our skier spends enough time at a deco
stop, he can very efficiently rid his body of nitrogen gradient.

Before we get to the overweight diver, there is still more to the skier's
issues----he CAN do an easy relaxed dive,  or maybe being towed by a
scooter, in which case his heart rate drops to about 45 beats per minute.
His breathing rate drops to about half of the breathing rate of the "average
diver", maybe even one fourth of it. While he is still exposing himself to
nitrogen gradient at depth, much less blood is being pumped now ( volume of
blood pumped is based on the number of beats per minute of the heart--- and
on how much blood the heart pumps per beat. Some athletes pump large amounts
per beat, others pump more normal amounts per beat, but their hearts can
pump at rates far higher than normal people---some can hit 240 beats per
minute.) Bottom line here is that this athlete is able to move
considerably less blood through his body and lungs, if he relaxes and slows
his heart,, due to his ability to efficiently power his body with a very low
heart rate and low volume of blood moved. So he is capable of
ingassing MUCH LESS nitrogen than the average diver, if he takes it very
easy on the dive ( as would say, a macro photographer, or a cave diver being
towed by a scooter).
Now we are looking at a person who has a huge range of decompression
obligation, which is based heavily on his own exertion rate, and his fitness
level. He might need quite less than the PADI tables may suggest on a macro
photo dive, or he might need a great deal more deco than the tables suggest,
if he does a fast spearfishing dive, or if he goes crazy during lobster
mini-season.

Now the heavy guy. Unlike some heavy guys who swim, cycle, or at least try
to train themselves aerobically, this guy works 10 hours per day, and has no
interest in aerobics. But he likes to dive.
Since VO2 max will be his ability to process oxygen, per kilo of body
weight, he has TWO strikes against him---One--his high body weight would
dilute any chance of having a high score if he trained aerobically , and
TWO, since he does NO aerobics, he has no peripheral adaptation, no
cardiovascular efficiency, and he starts off with a very low value for the
amount of oxygen he can take in---when this gets divided by his large body
weight, you can see how poor his gas exchange is going to be. This guy would
breath heavy doing a fast walk to the end of his driveway.  However, for 60
foot dives, he will ingass slower than the PADI tables would suggest.  But
he will also out-gass slower, meaning if his safety or deco stop is not
longer than the normal 3 minute stop most "average" divers perform, he will
not be able to rid himself of as much nitrogen as the average divers will.
And his high fat level will retain nitrogen longer than the average model
will predict for , since this is such a large area, with poor
vascularization--poor bloodflow. If he does multiple dives like this, he
will get into greater and greater trouble, as the table fails worse and
worse in representing his true off-gassing rate. Or , if the heavily
overweight diver goes to extreme duration on a deep dive, the deco model
will not protect him from his much slower offgassing performance.

The ultra fit diver, will have the tremendous safety advantage of keeping
their heart rate at a very low rate during the working portion of their
dive, through use of a scooter, or by attention to slow , efficient
movemement.  Additional advantage to these elite athletes will accrue
through knowledge of deep breathing techniques, which anyone on this list
can obtain by taking a good Yoga course. This will create better gas
exchange, and lower CO2 levels before they can reach levels which could
become uncomfortable. On the deco portion of the dive, heart rate can be
accelerated, and blood flow can be doubled, even tripled  easily. This will
provide them with a tremendous advantage in off-gassing, over the "average"
or "gas exchange challenged"  divers.   This is just one of the reasons that
a population of divers like the WKPP team, each with  the VO2 max levels of
a competitive athlete, will have no incidence of DCS, in a run of 1000 deep
penetration dives, while another population of fat, aerobically unfit divers
will have a HIGH rate of DCS incidents, and or other more serious
complications.

Since I and others have
condemned various individuals in the TDI and IANTD camps, for smoking
cigarettes and or pot, carrying huge ( I MEAN HUGE!!)  slabs of adipose
tissue around proudly,  for their lack of aerobic conditioning, and for
their failure to admit that  many of their top people are dangerously unfit
for technical diving, and potentially so far off the recreational tables by
their poor fitness, that they should not even dive normal recreational
profiles----It is with this in mind that this post runs long, but also
covers the physiological basis for many who we have condemned.

Testing for VO2 Max, can easily be done on a bicycle ergometer. Many gyms
with good personal trainiers can do this for you quite inexpensively. a
better measure still, would be to set up an ergometer in a chamber, simulate
250 or 300 feet, and see the DRAMATIC gas exchange   differences which will
occur between the 100 pound overweight diver, and the elite level athletic
diver. Underwater, this would be the difference between a fit diver being
slightly uncomfortable, having to pull themself upcurrent for half a minute,
and a dangerously overweight diver seeing a cool looking shipwreck, and the
increased heart rate alone,creating so much extra CO2 , that they get close
to toxic levels---even without trying to exert . The sooner someone starts
testing this as mandatory medical screening,  the sooner we will save the
lives of divers who have been IANTD or TDI certified to do something they
are ABSOLUTELY UNFIT for, and which puts them at EXTREME RISK.

Regards,
Dan Volker


--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]