simulation program

RWSamsel rwsamsel at aol.com
Fri Dec 16 09:49:33 EST 1994


>>> For our student courses in human physiology we are looking for
interactive software programs (windows preferred) for simulation
of cardiovascular regulation. Students should be able to vary specific
parameters of circulation and learn the effects of their manipulations.
<<<

Dr. Conradt:

My group has been working on such a program, although a number of the
features you describe have yet to be developed.  The system we have is
essentially a group of coupled differential equations, solved in real time
under a Windows interface, allowing students to change any parameter.  The
source of the work is a group of academic investigators who are trying to
"do it right" by providing relatively up-to-date models rather than merely
animating.  We have called the program SimBioSys (short for Simulation of
Biological Systems) and are expending considerable effort to bring it up
to date.

At present, we describe four cardiac chambers, interacting with peripheral
and pulmonary circulations with central arterial, arteriolar and venous
resistances and compliances, and include realistic activation curves and
dynamics for muscle action.  We have coupled it to lung inflation and
deflation dynamics, gas exchange, acid-base balance, renal function,
compartmental fluid transfer, and elementary control systems.  Since it is
a real time simulation, one second of simulated time is one second of real
time.  This has the consequence that one can't (yet) study long term
changes effectively, without running the simulation for days or weeks.

Even so, we have used it with some success to teach cardiovascular
physiology at the University of Chicago.  We reported an initial
experience in Advances in Physiology Education, (see Samsel et al., June
1994 issue).  It is equally applicable to respiratory physiology, although
we have not used it in as much detail there.

The phenomena you are interested in (orthostatic responses, adjustment to
exercise, erythrocyte shear stress) are beyond the current limitations. 
Orthostatic responses require a distributed parameter system, including
effects of gravity (although one should be able to do an adequate job
short of requiring partial differential equations).  Adjustment to
exercise should be a natural component, but we haven't worked it enough
yet.  Erythrocyte shear stress is more subtle, because it is so critically
dependent on the position of the cells within the flow stream.  Thus,
working it out demands a PDE analysis, which doesn't fit in a general
program.  Accordingly, apart from average lumped parameter measures of
(for example) Casson rheologic systems, correct analysis on a continuing
basis is outside the scope of a real time simulator.  

I am now working primarily for the company that is developing the
simulator as a commercial product, so this is a blatantly commercial
response.  For this I apologize.  To make up for my sin, let me at least
tell you about our serious competition.  The only other really serious
attempt I know of that is generally available is by Tom Coleman, at
Mississippi.  His system is called QCP (Quantitative Cardiovascular
Physiology).  His company is selling it inexpensively, and it is
unquestionably worth getting.  Tom is at tcoleman at fiona.umsmed.edu.  

His program differs substantially from ours: in his case, you tell the
computer what experiment to perform, and it calculates the answers and
plots them.  It uses steady state analysis of the cardiovascular systems,
rather than real-time physics, and gives answers describing minutes to
hours of evolution, with no description of the waveforms.  In contrast, we
provide real time waveforms for respiratory and cardiovascular systems,
but can't describe long term changes as well.  His system is more
sophisticated than ours with respect to cardiovascular reflex control.  We
are more sophisticated in integrating cardiopulmonary mechanical
interaction, tissue and pulmonary oxygen and carbon dioxide transport,
renal function, fluid balance, and so forth. 

Specific topic simulators exist for teaching specific systems -- I don't
know much about these but have seen a few good, focused projects. 

We have a demo version of our system; please send private email if you
want it.

-- Dick

Richard W. Samsel, MD
Scientific Director
Critical Concepts, Incorporated
Chicago, Illinois, USA




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