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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.med,sci.physics,sci.electronics
Subject: Biomedical Measurement "Challenge": Cardiac Output
Keywords: biomedical measurements, cardiac output, instrumentation
Message-ID: <2991@kitty.UUCP>
Date: 14 Feb 89 02:37:03 GMT
Organization: Recognition Research Corp., Clarence, NY
Lines: 56


	I thought I would take a stab at creating some interesting topics
of discussion (and speculation) concerning the application of engineering
to the challenges of biomedical measurement.  I will pose a measurement
problem, and see if anyone can propose a solution.  The problems should
be of interest to those who like to apply physics and electronics to real
world applications.  After a week or so of discussion, I will post the
actual methods used and the rationale behind them.  If this article
results in productive discussion, I will continue to pose these measurement
problems on a regular basis. if not, well, it seemed like an interesting
idea at the time. :-)

	A brief bit of background: I manage the development of scientific
and chemical process measurement and control instrumentation. I am both
an electrical engineer and biochemist, and have worked on a number of
biomedical instrumentation projects in the past 19 years that I have been
in private industry.  I have had firsthand experience with anything that
I may describe on this topic.  In recent years, though, most of my work has
been in the chemical process area, but I am still manage one active
biomedical instrumentation project.

	Some of you reading the Net are physicians or others who may have
intimate knowledge and experience with the subject matter; I would urge
that you sit back for a few days and see what some others have to say.

	Okay, here we go...

	Reduced to simplest terms, the heart is a pump.  As a pump it
therefore has an output rating, which is termed "cardiac output" and
is usually measured in liters/minute.  While the heart is actually a
synchronized dual pump, for the purpose of this discussion we are
dealing with the left side of the heart which pumps oxygenated blood
into the arterial system.  The left side of the heart has one outlet:
the aorta.

	Normal cardiac output ranges between 4 and 8 liters/min.  Cardiac
output is normalized to "cardiac index" which divides cardiac output
by surface area of the skin; normal cardiac index ranges from 2.5 to 5
liters/min/meter^2.  Cardiac output and cardiac index are valuable
measurements used in the diagnosis of cardiovascular disease.

	Now the problem: how can we measure cardiac output without
major surgery to expose the aorta and attach a flowmeter?  There
have been three major techniques used over the years, all of which
share a common principle.  Hint: bear in mind that we are taking a
relatively short-term measurement, so you can assume that cardiac
output is the same as venous return to the right atrium. You may also
assume that the output of the right ventricle into the pulmonary artery
is the same as the pulmonary venous return into the left atrium; i.e.,
both sides of the heart are pumping at the same rate with the blood
volume within the lungs remaining the same.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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