I am still thinking about Jean Cotterman's very interesting theorizing about
forces at work on the nipple, and I compliment her on initiating this
discussion. This discussion, and the ideological discussions are part of  what
makes Lactnet come alive for me.  Anyway, I want to add into the discussion the
work of Smith et al, Imaging Evaluation of the human nipple during
breastfeeding, Am J Dis Child 1988, 142:76-8. It is fascinating reading.  Their
visualiztions in real time, using ultrasound, found that the nipple extend to
2-3 times resting length, and that maximal milk ejection occurs at the point of
maximal thinning of the nipple during compression from jaws and tongue.  They
identified the tongue and jaws working rather more as a piston, with less
emphasis on a peristaltic wave.  So creation of negative pressure would be
important to get the nipple elongated, and the positive pressure componant would
be essential to get the nipple compressed to elicit maximal milk ejection.  The
dynamic interplay between creation of positive and negative pressure presupposes
several things:  a healthy baby who is strong enough to perform those functions,
a nipple that "fits" the baby's mouth and matches the baby's strength in terms
of ability to elongate and thin. If the baby can't manage the nipple due to
nipples' size, lack of elasticity, or due to weakness or oral cavity
restrictions (tongue-tie for instance) or if mom's milk supply is so low that no
amount of pulling and pressing results in milk expression, then the system
fails.  I think it is important to try to  understand  all these forces because
if you can identify where the system is failing and how, maybe you have a shot
at a correction.  I think babies are brilliant compensators, and often alter
their use of suction and compression to try to make things work when the
"normal" way doesn't produce results.
Some of those compensations doubtless create distortions of the shape of the
nipple.  I rather suspect that the shear forces may be more of an issue in flat
and inverting nipples which tend to telescope in when compressed.  They may pull
out very differently from non-tethered nipples.

Barbara Wilson-Clay, BSEd, IBCLC
Austin Lactation Associates, Austin, Texas
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http://www.jump.net/~bwc/lactnews.html

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