Thanks for the input.  This is a puzzling question.   The thing I wonder
about the IV analogy is that an IV is gravity fed and the reason that the
piggy-back IV is fed first is that the driving head behind it is higher and
of course, the flow control point (the restriction) is less than the
original IV (since it's flow is opened up more).

However, I would think that breastfeeding is primarily suction-based, with
more milk flowing as the baby evacuates the milk from the aereola and the
tube.  Of course breastmilk flow is highly complex from a hydraulics
standpoint since there is a MER and the action of the milk ducts and aveoli
that involve much more than gravity or simple pressure flow.  On the other
hand, the hydraulics of the SNS are more straightforward.  Basically there
is some gravity flow, whose magnitude varies based on tube diameter (if the
SNS is hung above the discharge point) and suction flow (from baby's action)
or just suction flow (if SNS is hung below the discharge point).  I don't
know exactly what would flow first - based on hydraulics, whatever has the
least resistance to flow would flow first.  It would probably vary from mom
to mom, depending on MER... and absolutely on the tube diameter and location
of the SNS tube in the baby's mouth (the efficiency of sucking is probably
less at the corner of the mouth then if it is located on the roof of the
mouth) and the elevation of the SNS with respect to the breast.

I would guess, if breastmilk supply was increased and MER was good and the
SNS was hung low with a small tube, the baby would first extract the
breastmilk and then begin to extract the fluid in the SNS.  However, hung
high, with a larger tube the SNS would definately flow before mom's letdown
started and may even exceed the natural flow of breastmilk.

What a fun question to ponder!

Elizabeth Bialek
Not a lactation professional, just a mom and an engineer


----- Original Message -----
From: Pat Bull <[log in to unmask]>
Sent: Friday, June 23, 2000 8:07 AM
Subject: Physics of SNS


Message text written by Lactation Information and Discussion
>physics of the sns, the milk comes
from the breast FIRST, whatever is there, and THEN from the sns.  This
has been an encouraging, reassuring fact for many mothers.        Anybody
out there care to explain/confirm this?
Hello Susan and Netters,
I try to use the analogy of the IV and a piggy-back IV.  Those not in the
medical field
let me try to explain.  An IV is hung high on a pole that solution flows
into mother's
arm/vein.  A piggy-back antibiotic bag of solution is then attached to the
same IV
already running and hung at a higher level.  The flow is opened up so it
flows into the
patients arm/vein at a faster flow than the larger IV.  After it is in, the
other IV will flow.  Of
course then a nurse will open that IV up to the flow that Dr. ordered.
Well, now imagine
having the SNS secured on the breast and tube opened up.  Mother's let down
comes
and it will flow at a faster pace than the SNS flow.  Also as mother's milk
increases, that
milk will flow at a faster pace than the SNS flow.  That is how you know
when mother's milk
has increased.  (one of the ways).  She will complain that the baby is not
taking as much
milk from the SNS.  That is usually a good sign.  Hope that is helpful.
Let me know if you
have any questions or concern.  Have a wonderful weekend.  Nice and sunny,
over 80, and
we are heading out to" veg" out in a place secluded in trees and a lake for
the weekend.
Pat Bull, RN,, IBCLC
The Breastfeeding Connection/Medela, Inc.
Naperville, IL



__________________________________________________
Do You Yahoo!?
Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com

             ***********************************************
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(TM)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html