Page 56 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 2

HEAT TRANSFER APPLICATIONS

IN BIOLOGICAL SYSTEMS

Liang Zhu
University of Maryland Baltimore County, Baltimore, Maryland

2.1 INTRODUCTION 33 2.4 TEMPERATURE,THERMAL PROPERTY,
2.2 FUNDAMENTAL ASPECTS OF AND BLOOD FLOW MEASUREMENTS 46
BIOHEAT TRANSFER 33 2.5 HYPERTHERMIA TREATMENT FOR
2.3 BIOHEAT TRANSFER CANCERS AND TUMORS 53
MODELING 36 REFERENCES 62

2.1 INTRODUCTION

Over the past 100 years, the understanding of thermal and mechanical properties of human tissues
and physics that governs biological processes has been greatly advanced by the utilization of fun-
damental engineering principles in the analysis of many heat and mass transport applications in
biology and medicine. During the past two decades, there has been an increasingly intense interest
in bioheat transfer phenomena, with particular emphasis on therapeutic and diagnostic applications.
Relying on advanced computational techniques, the development of complex mathematical models
has greatly enhanced our ability to analyze various types of bioheat transfer process. The collabo-
rations among physiologists, clinicians, and engineers in the bioheat transfer field have resulted in
improvements in prevention, treatment, preservation, and protection techniques for biological
systems, including use of heat or cold treatments to destroy tumors and to improve patients’ outcome
after brain injury, and the protection of humans from extreme environmental conditions.
In this chapter we start with fundamental aspects of local blood tissue thermal interaction.
Discussions on how the blood effect is modeled in tissue then follow. Different approaches for the-
oretically modeling the blood flow in the tissue are shown. In particular the assumptions and validity
of several widely used continuum bioheat transfer equations are evaluated. Different techniques to
measure temperature, thermophysical properties, and blood flow in biological systems are then
described. The final part of the chapter focuses on one of the medical applications of heat transfer,
hyperthermia treatment for tumors.

2.2 FUNDAMENTAL ASPECTS OF BIOHEAT TRANSFER

One of the remarkable features of the human thermoregulatory system is that we can maintain a core
temperature near 37°C over a wide range of environmental conditions and during thermal stress. The
value of blood flow to the body varies over a wide range, depending upon the need for its three
primary functions:

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