From: rhatcher@fnala.fnal.gov
Newsgroups: sci.skeptic
Subject: Re: Well known scientific facts
Date: 30 Sep 92 08:08:41 GMT
Article-I.D.: fnala.1992Sep30.140841.1
Organization: Fermi National Accelerator Lab
NNTP-Posting-Host: fnala.fnal.gov

In article <1992Sep29.185129.31476@mp.cs.niu.edu>, rickert@mp.cs.niu.edu (Neil Rickert) writes:
> In article <1aa443INNe2l@gap.caltech.edu> carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick) writes:
>>In article <1992Sep29.150200.31779@mp.cs.niu.edu>, you write:
[discussion on whether interior body temperature is a better measure of
"fever" than the rate of change of temperature of a thermometer]

> Your mistake is to think of the thermometer as the sink and the tongue
> as the source.  Actually the sink includes the tongue and other parts
> of the mouth, as well as the thermometer, and the source is the interior
> of the body.  

True.  That just means that *ANY* measurement of rate of change is
dependant on:
   1) mass of the thermometer (heat reservoirs ...)
   2) construction material of thermometer (heat conductivity ...)
   3) size/shape/construction/salivativity (to coin a word)
      of mouth (reservoir/conductivity)
   4) how good the person is at keeping the mouth closed :-)
      I think this is the kicker ... 

I think it's pretty obvious that it is damn near impossible to
calibrate a rate of change measurement into something reproducible
or even meaningful.  On the other hand the final temperature (for
any decently constructed thermometer) will be consistent.

My physics text would indicate that this is a differential equation
with boundary and initial conditions well describe by heat flow.
Intermediate solutions are going to be sensitive to the initial
condition everywhere in the system; while in the end (evolve (oops
probably bad word choice there :-) the system to T=infinty or
some approximation thereof), and the final thermometer temperture
will be independent of said conditions.

>      ...  The rate at which heat is being transferred from the
> interior to the periphery through the blood stream is the essential
> factor.  This is not a static conduction problem, but a problem with
> forced warm fluid flow.

I haven't been convinced that blood flow is a measure of anything 
important in the determination of a "fever".  Guess it depend on
your definition of fever:

fever: n. 1. Abnormally high body temperature.  2. A disease marked
by an abnormally high body temperature. 
[3. and 4. characterize "excitement" type fever]

Now this definition doesn't define "abnormally"; and I guess what
the new studies of "normal" body temperatures are saying is that
"abnormal" depends on the individual, their prior circumstances
(exercise for instance), time of day....  

> The rapidity of rise of the thermometer is not measuring the body
> temperature, but the rate at which blood is being pumped to the periphery.
> As the earlier discussion on sci.skeptic indicated, body temperature is
> not a very reliable measure of fever, particularly when it is a low
> grade fever.  

No.  I take the earlier discussion to mean that one can't rely on some
generic (possibly not well defined) "normal" temperature to be a good
indication on where to set the threshold for low grade fever for every
individual.  Now, if people came in generic brands with black and white
labels...

> I was answering a question about better measures.  And I
> was suggesting that the blood flow rate to the periphery, as indicated
> by the rapidity of the temperature rise in the thermometer, is a more
> reliable measure than is the temperature alone.

It may be that blood flow rate to the periphery is *some* indication
of a health problem.  But I think attempts to measure this using a
thermometer are doomed to failure.

>  -NWR

-robert (hatcher@msupa.pa.msu.edu)

(as for *my* physics background ... A.B's in Physics and Astronomy 
from UC. Berkeley; MS in Physics from Michigan State Univ; and *almost*
a PhD from MSU, sooner if I read less netnews :-)