Background information concerning the topics of the Second Symposium
of the IIfTC
Epistemology and the heart beat: Some foundational problems in electrocardiology
Jochen Schaefer*, Wolfgang Deppert**, Reidar K. Lie***
* International Institute for Theoretical Cardiology, Bad Orb, FRG
** Philosophisches Seminar der Christian-Albrechts-Universität zu
*** Department of Medical Humanities, East Carolina University, Greenville
Duration, shape and constancy of the action potential under defined conditions
are thought to reflect (the occurrence of) ionic processes across cellular
membrane structures (and within myocardial cells). Talking about biological
processes one usually is inclined to think that they occur with a certain
variance (Streubreite) and it is, therefore, somewhat surprising that
the underlying biochemical and biophysical processes seem to occur in
such a well-established fashion that depolarisation as well as repolarisation
of the action potential take place (all other conditions kept constant)
with a precision of less than a few milliseconds deviation. Particularly
the upstroke of the action potential is, compared to other phases of the
action potential, of extremely short duration (E. Carmeliet and J. Vereecke,
1979). This precision is also apparent under the conditions of induced
or spontaneous changes of rate and rhythm where shape and duration of
the action-potential show the phenomenon of electrical restitution in
a higly reproducible and mathematically treatable form.
Another remarkable and still mysterious property of heart muscle is its
repetitive self-excitation. This endows the heart with its intrinsic pacemaker,
allowing the regular excitation and contraction that is necessary for
maintenance of the circulation (H. Fozzard and M.F. Arnsdorf, 1986).
Most of the knowledge acquisition process in cardiac electrophysiology
has been devoted to the elucidation and the description of the mechanisms
which form the basis of rhythmic activity and which underlie the genesis
of the action potential and its various phases. In the past decades many
elegant experiments have been performed and various ingenious hypotheses
and theories of the field have been developed to explain the observed
(and produced) phenomena (see Denis Noble recent review article, 1984,
which he entitled: the surprising heart).
There are, however, some other fascinating aspects in this field of research.
We would here like to point out only two of them.
- Currently the Hodgkin-Huxley theory of the membrane potential is the
generally accepted theory in the scientific field. All experimental
findings are interpreted in light of this theory. However, an interesting
rival to this theory has been in existence for a long time (G. Ling
and R.W. Gerard, 1949; for a discussion, see also M.I.M. Noble and A.J.
Drake-Holland, 1986, and U. Ravens, 1983). The existence of two
such rival theories raises interesting epistemological questions. For
example, can we point to definite experimental evidence which refutes
Ling's theory? If not, why has this theory been almost universally rejected?
Are there any anomalies which can not be explained by the Hodgkin-Huxley
theory, but which can easily be explained by its rival? An examination
of these questions should be fruitful also for experimental research.
- The rhythmic contraction of the cardiac muscle cell is but one of
the periodic events in the human body. During recent years a body of
empirical knowledge has been accumulated on the importance of periodic
events for human health and disease. There also has been an interest
in the question of what it is that makes an organism aware of time itself
(W. Deppert, 1983). The question we would like to raise is whether it
is possible to model the heart in such a way that the periodic events
taking place there can reveal their importance for an understanding
of both normal and diseased cardiac function. Above we also have pointed
out the precision by which timed events occur at the molecular level.
This is in contrast with an "imprecision" at a higher level
(for example, it is probably not important for keeping up cardiac output
whether there are 69 or 71 heartbeats per minute). We would like to
ask whether an examination of these differences at different levels
can give us important insight into an understanding of cardiac function.
This may be another important example of a reduction problem.
Carmeliet E., and Vereecke, J.,
Electrogenesis of the action potential, in Handbook of Physiology, Volume
I, The Heart, 1979, 269-334.
Outline of a theory of system times
in Space, Time, and Mechanics, 1983, pp. 195-224, D. Reidel Publishing
Company, Dordrecht, Boston.
Fozzard, H.A., Arnsdorf, M.F.,
Cardiac Electrophysiology, in The Heart and Cardiovascular System, Scientific
Foundations, Volume 1, Raven Press, New York, 1986, pp. 1-30.
Ling, G., Gerard, R.W.,
The normal membrane potential of frog sartorius fibers
Journal cell. comp. Physiol. (1949) 34, 383-396.
The surprising heart: A review of the recent progress in cardiac electrophysiology
J. Physiol. (1984) 353, 1-50.
Noble, M.I.M., Drake Holland, Angela J.,
Discrepancies between scientific theory and practice in relation to physiological
Theoretical Medicine (1986) 7, 219-231.
Aktionspotentialform, Kontraktionskraft und Frequenz
Untersuchungen an Warmblüterherzen
Thieme Copythek, Georg Thieme Verlag Stuttgart, New York, 1983