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From: asuvax!stjhmc!f81.n129.z1.fidonet.org!Rob.Carr@ncar.UCAR.EDU (Rob Carr)
Newsgroups: sci.med.aids
Subject: HIV Infection and Chaos
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Date: 2 Oct 89 15:54:36 GMT
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Pardon me while I think out loud for a few moments.  Hopefully this will get
someone else thinking

One of the big areas in biology for the past 5 years has been chaos theory.
Stated simply, systems that are easily described may have very unpredictable
consequences.  A common example is the water faucet drip. At very low drip
rates, the drops are uniform and the time between drops remains the same.  When
the flow rate is speeded up, there may be differences in the drops as they
form, resulting in different time periods between the drops.  While the time
periods may be random, there are patterns that may be seen if the data is
represented properly.

Biological systems, since they are non-linear, tend to be fertile grounds for
chaos theory.  Already, the heart and the brain have shown that they may be
evaluated on this basis quite successfuly.  What is most important is that
chaos theory allows you to examine the transition from regular to chaotic
behavior while pointing out the crucial steps in the transition. For example,
for atrial fibrillation, the behavior of the T wave, which originates in the
other part of the heart, is actually more critical for the onset of AFIB.  So
now people are studying drugs that affect the ventricles to help with AFIB,
whereas before they only studied the atria.

If you've followed me so far, you've probably already guessed what's coming.
There are several chaotic periods or linear systems with chaotic regions nearby
involved in the progression of HIV.  I think.

First, there is infection itself.  If a person were injected with one HIV, it
is extremely doubtful that the person would become infected. Only when the
"stress" (i.e. # of viruses) is turned up does infection become more probable.

In at least some people, there is then a quiet phase where the virus is not
expressed.  This would be a linear period.  Yet this phase seems to progress
into a chaotic phase where antibodies become apparent and the virus replicates.

What pushes the system outside the envelope?

The course of HIV does not appear uniformly linear.  There are periods of
remission and periods of catastrophic system failure.  It sounds random. In
biology, there doesn't seem to be anything random, just chaotic.

If continuous p24 antigen levels, #s of infected cells, case histories, etc.
were available, it might be possible to draw the strange attractors (as they
are called) for AIDS.  We might learn very quickly some important facets of the
disease.  Perhaps steps we are now looking at are unimportant.  Perhaps there
are ultimate times to give AZT or DDI.  I think I can give an example here,
although it probably doesn't rely on chaos theory.  If someone were acutely
exposed to HIV, by say a blood transfusion or needle stick from a grossly
contaminated sample, an immediate regimine of AZT may prevent the body's
leaving the initial chaotic region, giving the system sufficient time to drop
to zero. Perhaps there are "constellations" of values that indicate the
potential for future improvement or collapse which would permit the altteration
of drug dosages.

One of the stranger things about chaotic systems is that they do not always
behave as expected.  For example, values of certain measurements which would be
considered "bad" may actually be indications to cut BACK on drugs.

--
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