See additional response at the end of the quoted message.
| -----Original Message-----
| John Gastineau wrote:
| >I recently asked an emergency physician about the
| necessity of taking
| >blood pressures while the patient is in a particular
| position.
|
| >The original discussion included many laments about
| the poor physics
| >understanding of physicians. While true, that many
| don't know as much
| >physics as they should (see laser story below) they
| do seem to have a
| >thorough knowledge of what works.
|
| After finishing giving blood to the Red Cross (while in a
| prone position), I have always been asked to raise the
| donation arm straight up (while still lying prone) and hold a
| piece of gauze over the puncture until all bleeding has
| stopped. Never have they asked me to lower my arm or rest it
| on the cot that I am lying on. Presumably, the lower blood
| pressure in the elevated arm makes it easier for the body to
| seal the still open wound.
In looking back I realized I omitted an important part of my comment:
Blood is donated from a vein, not an artery. What we call "blood
pressure" is arterial pressure. The behavior of the veinous system is
completely different--it is barely pressurized, compared to the arterial
system. Thus this blood donation example is irrelevant to the
discussion.
Thus to my point, that real world systems, particularly biological
systems, are sometimes a lot more complicated than the simplified models
we physicists like to use. There's a lot more to them than we might
conclude using a simple model, and so when we see an apparent conflict
between the physics explanation of a system, and practice in another
field, we might want to also look at the validity of our model, in
addition to questioning the practice.
I'm reminded of a workshop I gave recently. The data a teacher collected
did not quite fit the model in use. She was very troubled, and concluded
that there must be something wrong with the data collection equipment.
What was actually going on was that the model was only approximate. The
data were correct. She had a hard time accepting this. I'm currently
editing a new book for TI. Perhaps I should insert a few labs where the
goal is for the student to exclaim "This model stinks!"