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RE: [RC] Question for RC. - heidi"Thumps" is the common term for a condition more specifically known
as Synchronous Diaphragmatic Flutter, or SDF.
Anatomically, the phrenic nerve (which serves the diaphragm) runs
right across the heart. Nerves are normally "insulated" by a
myelin sheath--a sheath of living cells that contain an insulating
substance called myelin. Every time the heart beats, there is an
electrical discharge as electrolytes travel in and out of the heart
muscle cells triggering the cells to contract. Normally, because
of the myelin sheath, this has no effect whatsoever on the phrenic
nerve.
However, when certain e-lytes are way out of whack (usually calcium
and/or magnesium), the cells containing the myelin become unable to fend
off the electrical impulse that triggers the heart to beat, as e-lytes
begin to leak through the sheath. When that happens, each
heartbeat triggers an electrical impulse on the phrenic nerve as well,
causing the diaphragm to contract.
This can range in severity from a very mild tic with each
heartbeat to a great huge contraction. It is seen in the
flank--the flank looks like it is "pulsing" and if you put a
stethoscope on the horse and listen to the heart, you will find that
the "pulsing" of the flank is in rythm with the heartbeat. More
severe cases are what inspired the name of "thumping"--because that is
exactly what it looks like when you stand back and watch the flank
"thump."
Heidi
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