Introduction - Biofluidmechanics: An Introduction to Fluid Mechanics Macrocirculation and Microcirculation - page 3

fundamental engineering disciplines, such as systems and controls problems through the
design of new devices for medical imaging, rehabilitation, and disease diagnosis, among
others. The nature of biomedical engineering is thus interdisciplinary because of the need
to understand engineering principles and physiology both. The goal of biomedical engi-
neering is to mold these disciplines together to describe biological systems or design and
fabricate devices to be used in a biological or medical setting.
In this textbook, the focus is on mechanical engineering principles and how they are
related to biofluid mechanics. This is not to say that other engineering principles are not
or cannot be applied to biofluid mechanics. For this textbook, we will take the approach
that starts from the fundamental engineering statics and dynamics laws to derive the fluid
mechanics equations of state. Most of these equations should be familiar, but we will dis-
cuss and develop them in subsequent chapters where a review is needed. Most biofluid
mechanics problems deal with describing the flow in a particular tissue, which can be con-
sidered an extension or a special case of the fluid mechanics problems that have been
studied previously (if a fluid mechanics course was taken prior to this course). For exam-
ple, if we were interested in designing a new implantable cardiovascular device, we would
need to understand and consider not only the mechanical flow principles, but also the
material properties, the electrical components, and the physiological effects that the device
may have on the cardiovascular system. This type of problem approaches the heart of
what a biomedical engineer does: design a device to remedy a physiological problem and
describe the effects of that device in physiologically relevant settings. Some biomedical
engineers focus solely on the engineering design aspect, while others focus on physiologi-
cal applications. Herein we discuss both aspects of biofluid mechanics to solve multiple
types of problems.
1.3 SCOPE OF FLUID MECHANICS
Now that we have defined what a biomedical engineer is and what a biomedical engi-
neer does, the question should arise, “Why do we need to study biofluid mechanics?” We
will first answer the question, “Why should we study fluid mechanics?” and return to the
earlier question later. Any system that operates in a fluid medium can be analyzed using
fluid mechanics principles. This includes anything that moves in a gas (e.g., airplanes,
cars, trains, birds) or in a liquid (e.g., submarines, boats, fish), or anything that is designed
to have at least one boundary surface with a gas or a liquid (e.g., bridges, skyscrapers).
Situations may arise in which objects can be described as “flowing” through a fluid
medium (fish swimming). These types of situations need to be concerned with both the
flow of the object (fish) and the flow of the medium (water surrounding the fish). These
types of flow scenarios are common in biofluid mechanics in which cells exhibit fluid
properties and they are submerged in a moving fluid (red blood cells within the cardio-
vascular system). Stationary flow structures are concerned with the forces (drag, shear,
pressure) that can be transmitted from a flowing fluid to the structure. This is critical for
fluid to flow through any “channel,” which includes blood vessels, lymph vessels, and the
respiratory tract. Fluid mechanics principles can be used to describe all of these systems.