General Summary

Summary[top]

The aim of this work, has been to reassess the way the human heart regulates the physical pumping and circulation balancing modes.Two concepts have been proposed:

Concept 1

• The heart strives to do its pumping, with a fairly constant total volume and outer contour, in an environment conferring a substantial moment of inertia.

Concept 2

• The interventricular septum regulates ventricular stroke volumes to maintain proper balance between systemic- and pulmonic circulation.

The use of modern techniques, together with a thorough evaluation of ideas and experimental evidence in earlier published research, has provided the basis for this reassessment. The techniques were non-invasive (echocardiography) and invasive (gated thallium scintigraphy and coronary cineangiography).

The proposed pumping mode (the "gripping heart", Concept 1) is primarily characterised by a dominant force vector in the direction of the major heart axis. The old "Ventilebene" mechanism has been revived, and linked to the constancy of the outer heart contour, and thus to the environment in which the heart is working.

In the present study, it was found that the left ventricular wall outer contour displacement, on the average is less than 2 mm near the heart base. The displacement is diminishing in apical direction.

Atrio-ventricular valve plane displacement in the direction of the major heart axis at rest, was observed to be 19-22 mm.

These findings imply that left ventricle shrinks in systole by an approximately cylindrical segment, 19-22 mm in height, and with a radius of 34 mm. (The radius was obtained as a mean value from the left ventricle outer diameter, measured 2 to 3 cm below the atrio-ventricular valve plane.)

The cylindrical segment has a volume of 69-80 cm³, which coincides with the findings in young healthy persons 70-120 cm³, depending on body position [12, 25].

Contribution of atrial systole at rest, was found to be about 25 %.

The balancing mode by ventricular interference, Concept 2, is new.

It enables the heart to balance between right- and left ventricle, by a working principle different from that of a displacement pump. It is closely linked to the pumping mode, Concept 1. The comparative rigidity of the outer walls of the heart, makes the ventricular septum to exert a double regulation. This regulating mode ensures a proper working of right- and left ventricle, in case of extensive damage to other parts of the ventricles than the ventricular septum.

The introduction of these two concepts, implies a directional reorientation of force vectors for pumping and maintenance of circulatory balance.

The presently accepted concept is contraction/expansion of the ventricles in the direction of their lumen responsible for pumping, and needed for regulation (a common displacement pump), ad modum Starling.

That has been replaced by a new concept:

• a resultant force in the direction of the major ventricular axis (with respect to pumping action)

• a vector perpendicular to the major axis and ventricular septum (with respect to balancing mode).

The unique interplay of myocardial muscle fibres, cannot be reproduced by a single mechanical model.

By separation of the two vectors, it has been possible to design a double- and a single-pump, exhibiting the specific properties of the respective function.

The double-pump model, designed for constant total (left plus right chamber) output, simulates the balancing characteristics of the ventricular septum (Concept 2). It simulate a number of volume- or pressure-overload related heart defects, including different kinds of infarction.

The double-pump is in fact a displacement pump, and shares characteristics with many known artificial heart and left ventricular assist devices; example on characteristics are the quality of pulsating in- and outflow, and that inflow is not assisted by an "a fronte" effect. This is a major disadvantage at low filling pressures and high heart rates.

The single-pump is a new kind of displacement pump, not earlier found to be described.

A suitable name for this kind of pump can be dynamic-displacement pump.

This pump is working with "a fronte" effect (Concept 1), provides for smooth inflow and low filling pressure at high rates.

It also has an ability to control (and be controlled by) the inflow pressure in a closed loop circulation system. By doing this, it accomplishes another essential function of the heart, it is to keep left atrial pressure within a certain range, in order to protect the low pressure system from damage. It should thus be ideal to use, as a heart assist device. Its functional simplicity, and independence of sensor devices, should make it advantageous for safe long-term application.