Page 178 - Visions of the Future Chemistry and Life Science

Exploring human organs with computers 159

covering a lesion with the available skin graft. The brain is another organ
that is mechanically soft. Certain brain disorders are associated with vari-
ations in pressure in the cerebrospinal fluid that protects the brain from the
hard skull. Imaging techniques can provide information about the result-
ing changes in brain shape, but finite-element models of the fluid-structure
interactions have the potential to provide quantitative information about
the forces exerted on the tissue itself.

9.5 Cell interactions
Of growing interest world-wide is the possible carcinogenic effect of low-
frequency non-ionising electromagnetic radiation, such as that emitted
from power lines. Possible candidates for explaining sensitivity to electro-
magnetic fields are the gap junctions that exist between cells in many types
of tissue. These junctions are similar to the protein-based channels that
enable ions to pass across cell membranes, except that they span the extra-
cellular space between adjacent cells. Gap junctions provide cells with a
direct means of intercellular communication to co-ordinate the physiology
of large populations of cells.
The physical properties of gap junctions also influence the regulation
of cell growth, and the cell’s membrane voltage and frequency response.
There is some experimental evidence to suggest that the properties of gap
junctions change in the presence of electromagnetic fields. Finite-element
models provide a flexible and accurate way of assessing the effects of such
changes on the operation of large systems of cells.

9.6 The heart
Given that heart disease is the single largest cause of death in North
America and Europe, finite-element models of the human heart have great
potential clinical significance. The heart wall consists mostly of muscle,
comprising millions of electrically activated contractile cells that are typ-
ically 0.1mm long and 0.015mm wide. Note that the cell in Figure 9.2 is
from the heart. Heart contraction is activated by an electrical impulse that
is generated by cells in the heart’s pacemaker. This impulse spreads rapidly
through the tissue due to the high degree of electrical coupling between the
heart cells via gap junctions, ensuring that the whole organ contracts in a
synchronised fashion.