Biomedical Engineering Reference
In-Depth Information
Understand basic heart mechanics.
Explain how biomechanics applied to the
cardiovascular system is used to quantify the
effectiveness of the heart as a pump, to study
heart-vessel interaction, and to develop clinical
applications.
4.1 INTRODUCTION
Biomechanics combines engineering and the life sciences by applying principles from
classical mechanics to the study of living systems. This relatively new field covers a broad
range of topics, including strength of biological materials, biofluid mechanics in the cardio-
vascular and respiratory systems, material properties and interactions of medical implants
and the body, heat and mass transfer into biological tissues, biocontrol systems regulating
metabolism or voluntary motion, and kinematics and kinetics applied to study human gait.
The great breadth of the field of biomechanics arises from the complexities and variety of
biological organisms and systems.
The goals of this chapter are twofold: to apply basic engineering principles to biological
structures and to develop clinical applications. Section 4.2 provides a review of concepts
from introductory statics and dynamics. Section 4.3 presents concepts from mechanics
of material that are fundamental for engineers and accessible to those with only a statics/
dynamics background. Section 4.4 introduces viscoelastic complexities characteristic of
biological materials, with the concepts further applied in Section 4.5. The last two sections
bring all of this information together in two “real-world” biomechanics applications:
human gait analysis and cardiovascular dynamics. The human body is a complex machine,
with the skeletal system and ligaments forming the framework and the muscles and
tendons serving as the motors and cables. Human gait biomechanics may be viewed as a
structure (skeleton) composed of levers (bones) with pivots (joints) that move as the result
of net forces produced by pairs of agonist and antagonist muscles, a concept with origins
as early as 1680, as depicted in Figure 4.1 from Borelli's
De Motu Animalium
(
On the
Motion of Animals
). Consequently, the strength of the structure and the action of muscles
will be of fundamental importance. Using a similar functional model, the cardiovascular
system may be viewed as a complex pump (heart) pumping a complex fluid (blood) into a
complex set of pipes (blood vessels). An extensive suggested reading list for both gait and
cardiovascular dynamics permits the reader to go beyond the very introductory nature of
this textbook.
The discipline of mechanics has a long history. For lack of more ancient records, the
history of mechanics starts with the ancient Greeks and Aristotle (384-322 BC). Hellenic
mechanics devised a correct concept of statics, but those of dynamics, fundamental in living
systems, did not begin until the end of the Middle Ages and the beginning of the modern
era. Starting in the sixteenth century, the field of dynamics advanced rapidly with work
by Kepler, Galileo, Descartes, Huygens, and Newton. Dynamic laws were subsequently
codified by Euler, LaGrange, and LaPlace (see
A History of Mechanics
by Dugas).
