Introduction

This textbook will discuss basic fluid mechanics principles, flows within the macrocirculation, flows within the microcirculation, specialty circulations, and experimental techniques common to biofluid mechanics. The National Institutes of Health working definition of biomedical engineering states, “Biomedical engineering integrates physical, chemical, mathematical, and computational sciences and engineering principles to study biology, medicine, behavior, and health. It advances fundamental concepts; creates knowledge from the molecular to the organ systems level; and develops innovative biologics, materials, processes, implants, devices and informatics approaches for the prevention, diagnosis, and treatment of disease, for patient rehabilitation, and for improving health.” The focus of this textbook is biofluid mechanics, which is concerned with how biological systems interact with and/or use liquids/gases. For humans, this includes obtaining and transporting oxygen, maintaining body temperature, and regulating homeostasis.

Keywords

Biomedical engineering; biofluid mechanics; cardiovascular diseases; dimensions; units

Learning Outcomes

1.1 Note to Students about the Textbook

The goal of this textbook is to clearly describe how fluid mechanics principles can be applied to different biological systems and, in parallel, discuss current research avenues in biofluid mechanics and common pathological conditions that are associated with altered biofluids, biofluid flows, and/or biofluid organs. Classic fluid mechanics laws, which the reader may be familiar with from a previous course in fluid mechanics (but will be reviewed in Part 1 of this textbook), have been used extensively to describe blood flow through the vascular system for decades. One major goal of this textbook is to discuss how these laws apply to the vascular system, but we also aim to highlight some of the specialty flows that can be described using the same fluid mechanics principles. Part 2, Macrocirculation, and Part 3, Microcirculation, focus on the application of these classic principles to the vascular system and develop mathematical formulas and relationships to help the reader understand the fluid mechanics associated with blood flow through blood vessels of various sizes. Part 4, Specialty Circulations, describes fluid flows through the lungs, eyes, diarthroses joints, kidneys, and the splanchnic circulation, which are not traditionally covered in biofluid mechanics courses but are very important biological flows in the human body. Note that there are other important specialty circulations, which can be modeled using the fluid mechanics principles that will be developed in Part 1 of this textbook. We may touch on some of those circulations, but we will not fully develop an analysis of these flows. For the most part, similar fluid mechanics principles can be used to describe the specialty circulations with some slight modifications to accurately depict the particular special conditions associated with the circulation. Part 5, Experimental Techniques, briefly highlights different procedures that are currently being used in biofluid mechanics laboratories to elucidate flow characteristics. At the same time, we will highlight some of the current innovative work that is being conducted to elucidate biofluid mechanics phenomena. The overarching goal of this textbook is to establish a foundation for students’ future studies in biofluid mechanics, whether in a more advanced course or in a research environment.

In writing this textbook, we hope to meet the needs of both the students and the instructors who may use this textbook. We believe that this textbook is written in a way that instructors can use the material presented either as the sole course material (introductory biofluid mechanics course) or as the foundation for more in-depth discussions of biofluid mechanics (upper-division/graduate courses). However, an introductory textbook, such as this one, cannot include every detail of importance to biofluid mechanics. There are multiple exceptional references that can be used in conjunction with this textbook (some of which are highlighted in the Further Reading section). Therefore, we encourage you to visit your local libraries or to search the Internet for more in-depth details that are not included in this textbook. This textbook cannot and does not aim to replace traditional fluid mechanics or physiology textbooks, but it will provide the information necessary to (i) set a foundation for a broad biofluid mechanics discussion, (ii) analyze some of the particular biofluid mechanics principles, (iii) quantify some of the salient biofluid mechanics flows, and (iv) serve as a springboard for future more detailed and in-depth discussion. At the end of most of the chapters, we provide suggested references for the students and instructors, if more information is desired.

Your instructor and other students in your class are other good resources to learn about biofluid mechanics. However, we believe that you will learn these principles best by working example problems at home. We included extensive examples within the text, all completely worked out, so you can see the level of detail needed to solve biofluid mechanics problems. We also include various levels of homework problems at the end of each chapter for you to practice on your own time. Your success in this course will depend not only on the material presented within this textbook and from your instructor’s notes, but also on your willingness to comprehend the material and work biofluid mechanics problems yourself. We hope that this textbook can serve as a stepping-stone on your way to becoming experts in biofluid mechanics principles and applications. If you feel there are shortcomings or omissions in this textbook, please let us know so that the situation can be remedied in future editions.

1.2 Biomedical Engineering

One of the first questions that should arise when studying biomedical engineering (in this textbook the term biomedical engineering will be used interchangeably with bioengineering) is, What is biomedical engineering? The National Institutes of Health working definition (as of July 24, 1997) of biomedical engineering is

This definition is broad and can encompass many different engineering disciplines and, in fact, biomedical engineers can apply electrical, mechanical, chemical, and materials engineering principles to the study of biological tissue and to how these tissues function and respond to different conditions. Biomedical engineers also focus on many other 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 both engineering principles and physiology and apply concepts from both disciplines to your area of investigation. The goal of biomedical engineering 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. In parallel, thermodynamics equations will be developed for the study of heat transfer within biological systems. Most of these equations should be familiar, but we will discuss 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 considered 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 example, if we were interested in describing the blood flow through the coronary artery, we can use fluid mechanics principles, but we would also need to consider the mechanical properties of the blood vessel and how this may alter the fluid flow. Likewise, 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...