The mother in this case has pink nipples after breastfeeding.
Assuming the babies are suckling effectively, I would put forth the
following explanation for why her nipples turn purple with pumping.

Pumping involves alternating suction and absence of suction.  Normal,
physiologic breastfeeding involves both suction and peristaltic tongue
massage of the breast.  For every 'pull' there is a 'push': negative
pressure alternates with positive pressure, so you don't see this kind
of edema during the course of an effective breastfeeding session.
The color is of course because the tissue is filled with venous blood
unable to return into circulation.   This is in accordance with
ultrasound studies of the mechanics of breastfeeding.  Medela like to
emphasize the importance of the negative pressure part of the suckling
cycle because they, like all other pump manufacturers, have yet to
launch a breast pump on the market that is capable of reproducing an
infant's peristaltic tongue motion.

My dairy farmer friend was horrified when he became a father and saw
what kind of 'milking machines' were available for humans.  The ones
they make for dairy animals are worlds ahead, with peristaltic massage
coupled with suction so that the teats are treated almost the way they
are in a calf's (or goat kid's) mouth.   It is probably easier
technology to develop because of the anatomy of a cow's or goat's
udder and teats, contrasted with the shape of human breasts.

Since this mother seems not to be in pain despite the purple color,
and the babies are at breast at least sometimes now, perhaps the
solution is to live with it until she no longer needs the pump.  Hand
expression would also avoid the problem of vacuum-caused color
changes.

Rachel Myr
Kristiansand, Norway

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