Historical Background and Book Contents
11
windkessel is the mostly used
lumped model and its analysis is
elaborated in terms of total arterial system compliance and peripheral
resistance.
Extension of this model to more sophisticated later models
include those that vary from a linear rigid tube model to a freely moving
or constrained thin- or thick-walled, viscoelastic tube model. Some of
these utilize Navier-Stokes equations describing fluid motion, Navier
equations describing wall movement, and the equation of continuity
describing the incompressibility of the blood. Experimental deviations
from linear models are compared to nonlinear theories,
so
as to identify
the regimes of nonlinearities.
Distributed model provide more precise descriptions of the pressure
and flow behavior under varied conditions. However, they are generally
complex and time-consuming in identify individual parameters, and less
useful in daily clinical settings. Reduced models that are useful for
practical and clinical applications are discussed.
A
recently introduced
model to analyze the arterial wall behavior subject to varying pressure
amplitudes in terms of pressure-dependent compliance is elaborated.
This helps to explain the cyclical stress placed on the arterial wall and
how the arterial wall adjust to rapidly changing pressure amplitudes.
Once models of the arterial system have been developed, it is
necessary to verify the validity and limitations of these models.
Such
verifications
depend often critically on the specific design of the
experiments for measuring relevant hemodynamic parameters. For all
practical
purposes, these are pressure, flow, velocity, and vessel
dimensions.
Pulsatile pressure and flow and their transmission characteristics are
also the centerpoints of this chapter.
Here, the peculiarities and features
associated with pressure and flow waveforms
measured in their
respective anatomical sites are explained.
How the vascular beds
present as load to impede blood flow is quantitatively described in terms
of
the vascular impedance concept. Impedance, unlike resistance, which
remains constant, is complex with its magnitude changes with frequency.
Its usefulness is in its ability to include alterations in compliance,
resistance and inertance. This provides a useful description of the
changing arterial tree and individual vascular bed behavior. The manner
