I suggest you guys look up the definitions at
http://www.ux1.eiu.edu/~cfklm/zoo3100/lung31.html

and then use the numbers at
http://views.vcu.edu/~mikuleck/courses/resp/tsld023.htm

and do the math.

Jean-Marc

David Strike wrote:
>
> On Monday, March 12, 2001 2:45 PM, Lee Bell wrote:
>
> (snip)
> > I've deleted that
> > which we've both read to get to the points that seemed to be
> contradictory.
>
> > > Lung volumes obviously differ between individuals  based on size, sex,
> > > race, age, etc., so the figures that I've used are only approximate.
> > > However - and for discussion's sake - lets call the lung's total
> capacity
> > > (TLC) 6 litres:  the vital capacity (VC)- that amount of gas that can be
> > > breathed out after maximum forcible exhalation - say 4 litres:  And the
> > > residual volume(RV) - the amount of gas still remaining in the lung even
> > > after a forcible exhalation - 1.5 litres.  (The RV is usually about 25%
> of
> > > the TLC).
> > >
> > > The Tidal Volume (TV) is the volume of gas moved in and out of the lungs
> > > during a normal resting breathing cycle and is about 0.5 litres.  This
> is
> > > the figure that we really need to concern ourselves with.
>
> > Lee> If, at the end of an exhale, when is where you normally discover you
> > are
> > Lee> out of air, you have 2 liters of air in your lungs at 50 feet, 2.5
> ata
> > Lee> (atmospheres absolute, including the one atmosphere at the surface
> for
> > Lee> those not familiar with the terminology), if I have my math right,
> this
> > amount
> > Lee > of gas will expand to 5 liters at the surface.  If the lungs will
> hold
> > 6.5
> > Lee> liters on the surface, they are still within capacity.  No over
> > expansion
> > Lee> injury occurs, correct?
>
> > > Strike:
> > > I tend to disagree!  :-)
>
> > Stopping briefly at this point, there should be no disagreement on the
> > statements I made.
>
> Only if you're asking me to accept that a diver - instead of breathing
> normally - forcibly exhales all of the air from their lungs leaving only the
> residual volume remaining.
>
> > There are a lot of ifs there, but IF they are accepted,
> > then the conclusion is correct, right?
>
> Only IF we ignore the real world workings of the lungs.
>
> > Or am I still overlooking something?
> > If you have only 2 liters of gas in the lungs at the end of the exhale and
> > if you ascend from 2.5 ata, then you do wind up with 5 liters at the
> > surface, less than the capacity you suggest we use for discussion
> purposes.
>
> True.  But see my above comment.
>
> > > Let's be generous and assume that the diver, although swimming, is
> relaxed
> > > and has developed a rhythmic breathing pattern with a tidal volume of 1
> > > litre.  They only notice that they are out of air as they go to breathe
> > back
> > > in  after a normal exhalation cycle.  That still leaves - in this
> model -
> > 5
> > > litres of gas remaining.
>
> > Here's where the conflict arose.  You previously stated that the total
> > capacity we were going ot use is 6 liters, ie the largest volume one could
> > inhale.
>
> I spoke about total capacity being 6 litres - not a single inhalation.
> Re-read Tidal Volume.
>
> >On a normal inhale, one does not reach the maxumum.  In fact, one
> > is unlikely to come any closer to the maximum than they come to the
> minimum.
> > You've used 5 liters of gas at the end of an exhale when it is unlikely
> that
> > a person with a 6 liter capacity would have 5 liters of gas in their lungs
> > at the end of the inhale cycle.  Starting with what I can't accept as the
> > end of the exhale cycle means I can't accept the resulting volume at the
> > surface, even though we agree on the math.
>
> > > Ascending from a depth of 15-metres, (2.5 ata) the remaining volume of
> gas
> > > in the lungs would expand to 12.5 litres!!  (Needless to say that excess
> > > volume would have found some sneaky way of escaping the lungs!) :-)
>
> > No argument on this if you start with 5 liters.  It's beginning to come
> back
> > to me.  The inconsistencies went beyond my finding it hard to believe that
> 5
> > liters was the end of the exhale cycle to information that had been
> provided
> > from others and I'm going to have to go back and find that information.
> In
> > other words, I'm not as ready to resolve this as I thought.
>
> > I have a pretty good idea where I got my original volume and tidal
> movement
> > information and I can get it again, but it's not going to be immediate.
> I'm
> > going to have to contact my original source who may, in turn, have to
> track
> > down their source before providing it.
>
> > I know you've heard this before, but I'll be back.  In the interim, please
> > review your gas volumes to make sure you really meant that an individual
> > with a 6 liter total capacity has a volume of 5 liters remaining at the
> end
> > of the normal diving exhale cycle, a cycle that is generally a bit deeper
> at
> > both ends than a resting land cycle.
>
> > > I continue to believe that it is possible for someone to ascend from 50
> > feet without
> > > venting and without injury provided the initial volume was small enough
> > and that it is
> > > possible and even "not unlikely" that it was.  Having said this, it's
> > prudent to add
> > > that I don't recommend failure to vent to anyone.  The rule against
> > ascending while
> > > holding one's breath, later changed to breathe continuously, has a firm
> > basis in theory
> > > and practice.
>
> > This is still my belief, but it's important to me, for me to look further.
> > As I've mentioned, your volume at the end of the exhale cycle do not seem
> > logically correct or consistent with my recollection of information from
> > other sources (very sketchy at this point).  To satisfy my own curiosity,
> > I'll have to get the data again.  If you're interested in continuing, I'll
> > bring it back for your review, one way or the other.
>
> I'm perfectly willing to discuss diving issues with anyone.
>
> > > Granted that you have added a final disclaimer, but I still maintain
> that
> > it
> > > is impossible for a diver in a normal breathing situation and who
> suddenly
> > > discovers that they are out of air to do, as you state, and "ascend from
> > 50
> > > ft without venting".
>
> > I invited you to rejoin this discussion to resolve issues and for now
> other
> > reason.  If you are unwilling to participate on this basis, we can stop
> any
> > time you like.  One way or the other, I'm going to confirm or refute my
> own
> > opinions on this and you're welcome to help as much or as little as you
> > like.
>
> I accept you graciously made offer.
>
> Strike