I think Yael and Jack are right in clarifying that negative pressure per se
won't make a mom's nipples traumatized.  What I took Jack's comment to mean
was that the original question was just another foolish excuse to impose
time limits on bfg, and it is, as he suggests, ridiculous.

 Woolridge cites excessive neg. pressure causing trauma  in cases where
there is a problem with very low milk supply.  Additionally, other authors
describe that there is a dynamic interplay between negative and positive
pressure to extract milk. (The Breastfeeding Atlas has more discussion and
full citations).  Negative pressure holds the nipple in the mouth.  But
there is another role for negative pressure which is directly influential in
feeding. When the lower jaw opens wide, the sealed intra oral space slightly
enlarges.  Remembering  physics helps us see that enlarging a sealed cavity
will create a vacuum.  The milk in the breast is being pushed toward the
nipple by the positive pressure created by the contractions of let-down.  So
the fluid dynamics are that milk flow is facilitated when liquid flows from
a positive source towards a negative receiver.  So bottom line: creation of
negative pressure is important for flow and the pressure differential keeps
milk efficiently entering the chamber of the mouth.

Now what happens when a baby is impaired in some way?  For one example, say
you have a tongue-tied baby whose tongue mobility is so poor it can't come
forward to help the lips seal off the oral chamber.  This baby has to try
harder to create negative pressure.  So, since the baby is a brilliant
compensator, it may suck overly hard trying to achieve the same thing a
normal baby would do effortlessly. (The tongue-tied baby may also compensate
by increasing the amount of POSITIVE pressure too --i.e. by rolling in the
lips and by clamping down with the jaws to hold the breast in its mouth, but
that's another form of trauma).

Most of us have seen women whose nipple tissue has been damaged by cheap,
commercial grade pumps that create negative pressure in excess of safe
levels (vis a vis E. Egnell's research in the 50's).  The same phenomenon is
what I am talking about that can happen at breast, and what I understand
Woolridge to be addressing.  There is a reason for this, whether it be a low
supply with a slow flow rate that has a hungry baby desperately trying to
access milk, or whether it is a compensatory move baby uses to make up for a
deficit in another area of oral function.  Breastfeeding is a dynamic
interplay between positive and negative pressures, and it is interesting to
try to understand how it all works.  In the normal baby it is merely an
intellectual exercise because they don't need to try hard to make anything
work.  For the abnormal situation, we can be more useful if we understand
what the issues are.  This allows us to help substitute compensations that
may be less traumatic for the mother and more successful for the poorly
feeding infant.

Just a comment:  I don't think we have to be so attached to who is "wrong"
or who is "right" in these discussions.  We are colleagues trying to
understand a field of thought that is only now beginning to be elucidated.
The creativity of the debate is easily inhibited by taking "sides".


Barbara Wilson-Clay, BSEd, IBCLC
Austin Lactation Associates, Austin, Texas
http://www.lactnews.com

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