The article, "Impedance defined flow: generalization
of William Harvey's concept of the circulation - 370 years later" by Moser
M, Huang J W, Schwarz G S, Kenner T, and Noordergraaf A, in the International
Journal of Cardiovascular Medicine and Science, Vol. 1, No. 3/4, 205-211
1998, provides some light on the issue of how circulation takes place in
the circulatory system of embryos before the development of the heart.
Full article [683K].
It discusses the relation between flow and the
existence of valves in circulatory systems and points to and demonstrates
the existence of valve free circulation in both mechanical and biological
systems.
ABSTRACT:
"William Harvey (1628) attributed the flow of blood
through the cardiovascular system to the heart, providing the energy, and
to its valves, ensuring the preferential direction of flow. This report
presents a flow generating mechanism free of valves, dubbed impedance defined
flow.
"Nature offers examples where impedance defined
flow appears to be the sole perfusion mechanism. These include the human
foetus by the end of the third week of gestation. It proposes that addition
of valves in specific locations is a later development in evolution and
amounts to a special case of impedance flow, a suggestion that may profoundly
impact our current concept of the circulation.
SUMMARY:
"It is shown that the impedance defined flow principle,
introduced in this paper, is capable of producing average flow. Any compliant
fluid conducting system of which a part is subject to pressure oscillation,
and which displays assymetric flow impedances tends to produce unidirectional
flow. This constitutes a generalization on Harvey's view that blood moves
around the circuit solely by the pumping action of the heart, thereby creating
a new field of research within and without the cardiovascular system. Judicial
placement of the valve can improve the pumping efficiency of the system.
"The fact that valveless circulatory systems can
be found predominantly in simpler animals suggests that valves constitute
a refinement developed later in the evolutionary process. Also, in early
development, valves appear only after the creation of flow in the embryonic
circulation giving rise to the suggestion, that flow contributes to the
location and formation of the valves." Copyright 1998: Medical
and Engineering Publishers, Inc.
In general this article supports, as one example,
what was pointed to already in 1894 by an Austrian physician, who described
the hydraulic ram as a more appropriate model of the function of the heart
than the pump model.
Twenty-six years later, this view was brought forward
again by Rudolf Steiner in a lecture
as part of a series
of lectures on medicine, leading to the foundation of anthroposophical
medicine, pointing in the direction of the understanding of Aristotle
of the heart, not primarily as a "will" organ, but as a "sense" organ.
The general intermediary nature of the heart in
the human organism points to a degree of onesidedness in both perspectives.
For more on Rudolf Steiner's view of the heart
in the human being, see a
lecture.
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2004-2006: Robert Mays and Sune Nordwall
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