Biomedical Engineering Reference
In-Depth Information
FieldML models
CellML models
CellML models
Fig. 8.13.
Types of models used in the multiscale modelling hierarchy. Models based on systems
of ODEs and algebraic equations are shown in blue (so called 'lumped parameter' models) and
these are encoded in CellML. Models that require the solution of partial differential equations are
shown in pink and are encoded in FieldML. The FieldML models link to CellML models at material
points in the tissue. The arrows above are shown as unidirectional but, in fact, information flows
both ways. The models shown in gray will be linked into the cardiac modelling hierarchy in the
future.
grained approximations of molecular dynamics models, as shown on the lower right
in Fig. 8.13.
We next discuss building composite models by combining cellular models of dif-
ferent physical processes. The tool used to build the composite myocyte model is
OpenCell (see Fig. 8.3).
Building a composite cell model
Along with cardiac excitability (included here via Pandit et al., 2001), several other
cell level processes need to be modelled since they influence the electrical behaviour
of the cardiomyocyte. Most importantly, cardiac cells contract. The wave of electri-
cal propagation passing over the cell membrane and down into the invaginations of
this membrane, called 'transverse-' or 'T-tubules', releases Ca from internal stores
located at points where the internal reticular network called the 'sarcoplasmic' retic-
ulum (responsible for soaking up calcium from the cytoplasm) is adjacent to the
T-tubules. Release of Ca from these stores through ryanodine receptors is initiated
by voltage-activated Ca channels in the external membrane (included here via Hinch
et al., 2004). The released Ca diffuses to troponin-C binding sites on the contractile
myofilaments and initiates force production (included here via Niederer et al., 2006).
It is necessary to consider Ca transients and mechanical contraction along with the
