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A number of questions, intimately related to the way in which the human heart accomplishes its purpose, lack consistent answers. Probably the most important question concerns the general validity of the Frank-Starling relationship for in vivo output and intraventricular output balance regulation. This situation affects a wide range of problems in heart physiology and cardiology. Together with some initial observations with non-invasive heart-imaging techniques, it induced me to reassess the physical action of the heart. This is the main objective of this thesis.
The reader should be aware that such a reassessment must of necessity contain views and interpretations of well-known, or sometimes less well-known, findings by other authors. There is a great complexity of the matter involved, and also an enormous amount of often contradictory evidence gathered up to the present day. Therefore is it extremely difficult to strike a fair balance between what is known, and what is new.
An outline of the historic development of heart physiology is given.
After that an attempt to establish tentative criteria for how to define "current views" on the pumping action and regulating function of the heart is made.
This is followed by an outline of the topographic anatomy of the heart and of some basic physical principles. That is believed to be of particular importance for understanding the pumping action of the heart.
A discussion of the physiology of the working heart in situ links established facts with new ideas. For the sake of clarity, pumping and regulating modes are presented in the form of two basic concepts, which are supported by new experimental evidence:
These results allow prediction, or explanation of, ventricular septum displacement in a number of volume- or pressure-overload-related heart defects usually not encountered as "pure" defects. The elucidation of the proper working and regulating modes of the heart, and the experimental findings with the double pump was essential; these enabled me to design a new self-regulating single pump. It is described, and its action is explained and compared with the pumping action of the heart.
There is a considerable number of monographs in the history of heart physiology and cardiology [165] , as well as chapters in books on the general history of medicine devoted to these topics. But they do not cover development up to the present day. It is thus meaningful to provide the reader with an updated view, which should help in understanding the situation in the field today.
Stenonis [169] was the first to describe the complex anatomy of cardiac muscle 1664.
The 18th century refined the anatomical knowledge of the heart (cf. Haller [64]) but added little to the already established principles. A notable exception is the work of Hales [63] on blood pressure and heart output.
During the last century, interest in this field was revived, first by rapid development of auscultatory techniques and later in a more general way. The concept of active systolic filling of the atria was put forward for the first time in 1843 by Purkinje [137]. His ideas were taken up by Henke [76], Hauffe [71], Böhme [31], Benninghoff [8], Hamilton and Rompf [65] and others.
Another path of investigation was pursued by Starling and his group [129] based on the pioneering work of O. Frank, a pupil of C. F. W. Ludwig (a German scholar, who could be considered as the father of heart physiology of today).
The second world war changed the scientific scene. The center of gravity shifted in this area (as in many others) to the United States (Berglund, Braunwald, Brecher, Gauer, Hamilton, Opdyke, Sarnoff, Rushmer and others). The post-war period experienced a rapid increase of biomedical knowledge. The Starling tradition, which had the appeal of a well-defined theoretical basis and a repertoire of established experimental models, prevailed [17 , 18]. A decisive factor in the success of the Starling school, could well have been its elegant explanation of how intraventricular output balance is maintained. Functional heart anatomy in general did not devote any attention to this important problem.
The basic concept of the heart as a double pump with four chambers and four valves goes back to Harvey [70, 180]. He also recognised the consecutive contraction of the atria and ventricles. Harvey [70] and Lower [106] found that by the contraction of the ventricles the AV-plane and apex move nearer to one another. Ventricular filling is effected by an "in-rush" of blood during diastole [106]. Lower gives an explanation for the walls of the right ventricle being thinner than those of the left. He also had quite a clear conception of the lifting of the tricuspid- and mitral cusps as the mechanism for their closure.
The 1970's saw a renewed interest in basic problems of heart physiology - an interest which subsided again in about 1980. Thus, much of the relevant newer work cited in this thesis comes from that period. Access to new non-invasive techniques did not alleviate the fragmented situation. A large number of variables (with combinations), are still used to characterise the state of the heart (normal and diseased) in a wide range of models and experimental conditions (cf. [97]). The prevailing situation is manifest in some of the most influential textbooks and surveys on heart physiology and cardiology [2, 4, 5, 11, 15, 16, 25, 43, 91, 128, 166].
There has been sporadic criticism of the established main line of teaching [101, 120, 124], especially for lack of relevance with respect to pertinent clinical questions in cardiology [37, 88, 146]. This criticism does not encompass the tremendous increase of knowledge about the neural and humoral regulation of the heart; within the last 25 years, an accumulation which is of great and uncontested clinical and scientific value have been done.
Modern textbooks and surveys in the field, differ among themselves about the importance they ascribe to various events. For example events as:
Usually, the physical pumping action of the heart and its topographic anatomy are either treated rather cursorily, or are entirely omitted. The biology, biochemistry and biophysics of the single heart muscle fibre are accorded a central explanatory role. That does not bridge the gap between what is observed at the macroscopic and the microscopic levels, especially regarding the pumping action of the heart as a whole.
The pumping heart may be seen as the solution of two separate bioengineering problems:
Although these problems are intimately linked, I will refer to them separately when possible.
There is no disagreement about basic anatomical facts, although they are most often treated rather superficially. The heart is a cyclically moving muscle. There is no single configuration that adequately describes the three-dimensional relationship between its parts. Its pumping function is usually characterised by ventricular pressure/volume diagrams [153], ejection fractions [123] and the like. Little attention is paid to changes in its three-dimensional shape over the cardiac cycle.
It is obvious that the heart muscle contracts when pumping and that there is a change of volume in the chamber.
The view that the heart muscle is pumping by contraction with ensuing volume changes of its chambers, is trivial. However, the working mode of the heart is not obvious due to anatomic complexity of the heart muscle syncytium (in fact a pseudo-syncytium [170]); neither due to its interplay with surrounding tissue, nervous and humoral control, the influence of static and dynamic pressure components of the incoming and ejected blood etc.
Many recent texts (e.g. [6, 11, 15, 16, 25, 60, 61, 62, 69, 73, 91, 128, 144, 147, 159, 161, 166, 170]) either describe ventricular systole as a rather uniform
contraction, or do not dwell on this matter at all. Other authors [2, 5, 43] give
a more complete description i.e., by assigning physiological significance to ventricular
contraction in the direction of the major heart axis. Few (e.g. [4, 49])
refer to classic studies [8, 31] in physiological heart anatomy.
There is considerable divergence of opinion regarding ventricular diastole - for example,
on the role of venous pressure, ventricular compliance, diastolic suction, the role of the
pericardium, etc. The function of atrial systole is also a matter of discordance.
The Frank-Starling law1 [129]
governing the extension of sarcomeres/contractile force relationship, usually occupies a
central place in the interpretation of experimental results, although some authors think
its importance is more limited.
1 For convenience, this term will be used, although it does not give due credit to the discoverers of the relationship between presystolic muscle fibre length and responsiveness (Schlant et al. [159]).
One should discern between short- and long-term regulation. Long-term regulation is on the whole well understood. The same cannot be said of short-term regulation. The present situation is described by Sokolow and McIlroy (p.19 [166]):
"The circulatory control mechanisms respond to any change in cardiac output within a couple of beats and act to modify cardiac performance and change the hemodynamic state. It is thus difficult to determine the cause of changes in cardiac output on a beat to beat basis, and clear relationships between cardiac filling and stroke volume, which can be seen in isolated heart preparations in the laboratory, tend to be masked in patients. It is possible, however, to recognise the directions of change and, if there is an increase in cardiac output with a decrease in filling pressure, this can be clearly seen to be beneficial whether it results from the Frank-Starling mechanism, from increased intensity of excitation-contraction coupling, or from both".
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