Introduction - Biofluidmechanics: An Introduction to Fluid Mechanics Macrocirculation and Microcirculation - page 4

Also integral to the study of fluid mechanics is the design of fluid machinery. Fluid
machinery includes pumps, turbines, and anything that has a lubrication layer between
two moving and usually solid parts. Typically, fluid machinery comes into play in the
design of heating and ventilation systems, cars, airplanes, and a long list of other devices/
systems. Fluid mechanics is not an academic problem, but one that every engineer will
face at some time during his or her career. This textbook is not going to replace a standard
fluid mechanics text or a fluid mechanics course. Instead, we use fluid mechanics as a
starting point to describe one particular application of fluid mechanics: biological fluid
flows.
1.4 SCOPE OF BIOFLUID MECHANICS
So, why should we study biofluid mechanics? First, your body is composed of approxi-
mately 65% water. All cells have an intracellular water component and each cell is
immersed within an extracellular water compartment. There are some forces that are
distributed and transmitted through this water layer that act on the immersed cells. Also,
some cells in your body are non-adherent cells (i.e., red blood cells, white blood cells,
platelets). These highlighted cells are convected through your blood stream (within the
cardiovascular system) and experience many types of fluid forces (including shear forces
and pressure forces). Gas movement (such as oxygen and carbon dioxide exchange within
your lungs) can also be described by fluid mechanics principles. Joint lubrication, a major
research area of biofluid mechanics, is critical to locomotion: with the degeneration of the
lubrication layer, movement becomes difficult. Prosthetics cannot be designed without
fluid mechanics. It is our hope that throughout this textbook, the readers will understand
how fluid mechanics laws can be applied to biological systems, and the significance of
fluid mechanics laws to the biological system as a whole.
Furthermore, the design of many implantable devices must consider fluid mechanics
laws. Obvious examples are those devices that are directly implanted into the human
body and are in contact with blood, such as stents and mechanical heart valves, among
others. However, a total artificial heart is a pump that will have a biological fluid flowing
within it and replaces a portion of the cardiovascular system. Other examples of
implantable devices that involve biofluid mechanics include extracorporeal devices that
must maintain steady flow without aggravating cells or introducing harmful chemicals
(for dialysis); contact lenses that must consider the wetting of the eye, as well as gas diffu-
sion to the eye, to function properly. Indeed, nearly every device intended for biological
use will have to consider fluid mechanics laws, which are critical for proper design and
functioning of the device.
Why is biofluid mechanics so critical to study? According to the American Heart
Association, in 2011, more than 82,500,000 people in the United States had at least one cardio-
vascular disease. The majority of these cases are associated with high blood pressure
(approximately 74 million people; this number only includes people older than 20 years) or
coronary heart disease (approximately 18 million people; note that some of these patients
can overlap with the first group). Also, cardiovascular diseases are the cause for