Table Of ContentMicrowaves
and
Thermoregulation
Edited by
ELEANOR R. ADAIR
John B. Pierce Foundation Laboratory
and Yale University
New Haven, Connecticut
1983
ACADEMIC PRESS
A Subsidiary of Harcourt Brace Jovanovich, Publishers
New York London
Paris San Diego San Francisco Sao Paulo Sydney Tokyo Toronto
Copyright © 1983, by Academic Press, Inc.
ALL RIGHTS RESERVED.
NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR
TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC
OR MECHANICAL, INCLUDING PHOTOCOPY, RECORDING, OR ANY
INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT
PERMISSION IN WRITING FROM THE PUBLISHER.
ACADEMIC PRESS, INC.
Ill Fifth Avenue, New York, New York 10003
United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
24/28 Oval Road, London NW1 7DX
Library of Congress Cataloging in Publication Data
Main entry under title:
Microwaves and thermoregulation.
Includes index.
1. Body temperature--Regulation-Congresses.
2. Microwaves-Physiological effect-Congresses.
I. Adair, Eleanor R.
QP135.M465 1983 599\0188 83-2653
ISBN 0-12-044020-2
PRINTED IN THE UNITED STATES OF AMERICA
83 84 85 86 9 8 7 6 5 4 3 2 1
This book is dedicated to
JAMES DANIEL HARDY
for his contributions to thermal physiology and his interest in the thermal
consequences of microwave exposure.
Contributors
Numbers in parentheses indicate the pages on which the authors’ contributions begin.
Eleanor R. Adair (231, 359), John B. Pierce Foundation Laboratory and Yale Uni
versity, New Haven, Connecticut
Larry G. Berglund (15), John B. Pierce Foundation Laboratory, New Haven, Connect
icut
Michel Cabanac (307), Departement de Physiologie, Faculte de Medecine, Universite
Laval, Quebec, Canada
Chung-Kwang Chou (57), Bioelectromagnetics Research Laboratory, Department of
Rehabilitation Medicine and Center for Bioengineering, School of Medicine and
College of Engineering, University of Washington, Seattle, Washington
John O. deLorge (379), Naval Aerospace Medical Research Laboratory, Pensacola,
Florida
Ralph F. Goldman (275), U.S. Army Research Institute of Environmental Medicine,
Natick, Massachusetts
Richard R. Gonzalez (109), John B. Pierce Foundation Laboratory and Yale University
School of Medicine, New Haven, Connecticut
Arthur W. Guy (57, 401), Bioelectromagnetics Research Laboratory, Department of
Rehabilitation Medicine and Center for Bioengineering, School of Medicine and
College of Engineering, University of Washington, Seattle, Washington
H. Craig Heller (161), Department of Biological Sciences, Stanford University,
Stanford, California
Robert B. Johnson (401), Bioelectromagnetics Research Laboratory, Department of
Rehabilitation Medicine and Center for Bioengineering, School of Medicine and
College of Engineering, University of Washington, Seattle, Washington
Don R. Justesen (203, 461), Neuropsychology and Behavioral Radiology Laborato
ries, Kansas City Veterans Administration Medical Center, Kansas City, Mis
souri, and Department of Psychiatry, The University of Kansas School of Medi
cine, Kansas City, Kansas
Jerome H. Krupp (95), Radiation Sciences Division, USAF School of Aerospace
Medicine, Brooks Air Force Base, Texas
W. Gregory Lotz (445), Bioenvironmental Sciences Department, Naval Aerospace
Medical Research Laboratory, Pensacola, Florida
RichardH. Lovely (401), Neurosciences Group, Biology Department, Battelle, Pacific
Northwest Laboratories, Richland, Washington
ix
X Contributors
Sol M. Michaelson (283), Department of Radiation Biology and Biophysics, The
University of Rochester School of Medicine and Dentistry, Rochester, New York
Sheri J. Y. Mizumori (401), Department of Psychology, University of California,
Berkeley, California
John M. Osepchuk (33), Raytheon Research Division, Lexington, Massachusetts
Herman P. Schwan (1), Department of Bioengineering, University of Pennsylvania,
Philadelphia, Pennsylvania
Steven G. Shimada (139), John B. Pierce Foundation Laboratory and Yale University
School of Medicine, New Haven, Connecticut
Ralph J. Smialowicz (431), Immunobiology Section, Experimental Biology Division,
Health Effects Research Laboratory, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina
Joseph C. Stevens (191), John B. Pierce Foundation Laboratory and Yale University,
New Haven, Connecticut
John T. Stitt (139), John B. Pierce Foundation Laboratory and Yale University School
of Medicine, New Haven, Connecticut
Jan A. J. Stolwijk (297), John B. Pierce Foundation Laboratory and Department of
Epidemiology and Public Health, Yale University School of Medicine, New
Haven, Connecticut
Charles Süsskind (239), College of Engineering, University of California, Berkeley,
California
C. Bruce Wenger (251), John B. Pierce Foundation Laboratory and Department of
Epidemiology and Public Health, Yale University School of Medicine, New
Haven, Connecticut
Preface
This volume is the proceedings of a symposium hosted by the John B. Pierce
Foundation and held at Yale University, New Haven, Connecticut, on October 26-27,
1981. The goal of the symposium was to bring together engineers, physical scientists,
physiologists, and psychologists to discuss how nonionizing electromagnetic radiation
deposits thermalizing energy in biological tissues and the means by which this energy
may be detected and effectively managed by the conscious organism.
Much is known about the mechanisms by which warm-blooded organisms achieve
and maintain a characteristic, stable internal body temperature in the face of environ
mental thermal stresses. Exposure to nonionizing radiation of the microwave frequen
cy range can provide a unique thermal challenge to deep, as well as peripheral, body
tissues that must be dealt with by these same mechanisms.
Recent developments on two broad scientific fronts indicated that an interdisciplin
ary meeting would be both timely and productive. First, research into the biological
effects of exposure to radiofrequency radiation has advanced considerably during the
past 6-7 years, roughly since a symposium held at the New York Academy of
Sciences. Many of the suggestions for future needs and directions, offered by Prof.
Arthur W. Guy on that occasion, have already occurred and more are in various stages
of accomplishment. Research emphasis in this field has shifted from high-intensity to
low-intensity exposure as scientists probe more and more subtle biological effects.
With this shift in emphasis has come the realization that an increase in body tempera
ture of an experimental animal exposed to microwaves implies a breakdown of
thermoregulatory mechanisms. On the other hand, low-intensity exposures, previous
ly dubbed “nonthermal,” usually initiate immediate and efficient thermoregulatory
processes that ensure the constancy of the internal body temperature. Knowledge of
basic thermoregulatory processes is clearly necessary for the full understanding of the
responses of conscious animals in the presence of radiofrequency fields.
The second development is the recent surge of interest in the use of microwave
diathermy and other means to produce highly localized hyperthermia as an adjunct to
effective cancer treatment. Localized tissue heating is known to increase local tissue
blood flow and to alter metabolic processes in the affected tissues. However, such
treatments are employed only in the clinic, not in the laboratory, with the result that
much potential data that could add significantly to our understanding of thermoregula-
xi
xii Preface
tory processes are not recorded. Students of thermal physiology, as well as cancer
therapists, would benefit from an increased awareness of microwave techniques for
producing localized hyperthermia as well as the particular problems of energy absorp
tion attendant upon microwave exposure.
It was most appropriate that the symposium on microwaves and thermoregulation be
hosted by the John B. Pierce Foundation. This institution was founded in 1924 to
“ . . . promote research, educational, technical, or scientific work in the general
fields of heating, ventilation, and sanitation, for the increase of knowledge to the end
that the general hygiene and comfort of human beings and their habitations may be
advanced.”
In 1934, the Foundation sponsored the organization of The John B. Pierce Founda
tion of Connecticut, Incorporated which owns and operates the Laboratory in New
Haven. Since its founding, the Laboratory has been affiliated with Yale University.
Many of its staff contributed to this symposium; their cooperation and enthusiasm
helped to make the symposium a reality.
The symposium and this volume would not have been possible without the generous
support of the Tri-Service Electromagnetic Radiation Panel, TERP, representing the
Army, Navy, and Air Force. These funds were administered through AFOSR Grant
81-0211. Additional support has been provided by the John B. Pierce Foundation.
To the participants, who enthusiastically exchanged ideas and thereby expanded our
knowledge of this interdisciplinary research area, I extend my thanks. Many others
made substantial contribution to the success of the symposium and the preparation of
this proceedings volume. I thank Dr. James D. Hardy, former Director of the John B.
Pierce Foundation Laboratory, who first urged me to convene this meeting, Dr.
Lawrence E. Marks for his presentation at the symposium, not recorded herein, and
Dr. A. Pharo Gagge and Dr. Hardy for serving as session chairmen. Ms. Janice Gore
of the Yale University Medical School Office of Continuing Education worked
tirelessly on the symposium arrangements. Special thanks are offered to Mrs. Barbara
Adams for her assistance in all phases of this enterprise. I greatly appreciate the effort
of Ms. Joan Batza who prepared the final copy used to reproduce these proceedings and
the expertise of Mrs. Gillian Akel who prepared the subject index to this volume.
Eleanor R. Adair
MICROWAVES AND THERMOREGULATION:
HISTORICAL INTRODUCTION
Herman P. Schwan
Department of Bioengineering
University of Pennsylvania
Philadelphia, Pennsylvania
I. INTRODUCTION
Building models of the thermoregulatory system and gain
ing insight about how RF energy is absorbed by the human
body have been two distinct disciplines with very little
cross-fertilization for several decades. Their historical
developments have much in common. In both cases, models of
the human body were introduced which were initially very
simple. These models were eventually replaced by increas
ingly complex models providing ever-increasing predictive
capability. Now these two discipline have begun to merge
for several reasons:
1. Determination of thermal tolerances to radiofrequency
(RF) energy absorption requires the use of advanced
thermoregulatory models. Past and presently antici
pated RF-safety standards for man are based on the
concept that average total energy absorption should
not exceed either the basal metabolic rate or about
40% of this value. More attention is directed now to
strongly-localized energy absorptions. The concept of
permissible total thermal load should be complemented
by stating the permissible local SAR-values and tem
perature increases. Application of appropriate ther
moregulatory models may be required to translate
specific absorption rates (SAR) into temperatures.
2. The controlled application of RF energies may well
become a valuable research technique to further our
Microwaves and Thermoregulation Copyright © 1983 by Academic Press, Inc.
1 All rights of reproduction in any form reserved.
ISBN 0-12-044020-2
2 Herman P. Schwan
understanding of thermoregulatory processes, a point
first made years ago by Hardy to this writer.
3. Local temperature elevations caused by absorption
of RF and microwave (MW) energies may well become a
valuable therapeutic technique to reduce abnormal
tissue. Appropriate consideration of man's thermo
regulatory system is required in order to translate
local SAR distributions into temperature elevations in
clinical hyperthermia.
I will first outline the history of thermal RF-tolerance
and of thermoregulation and then conclude with a survey of
recent attempts to merge these two areas. The models to be
considered are indicated in Table I.
TABLE I. Models of Electromagnetic Heat
Deposition and Thermoregulation
1. RF and MW Energy Deposition
2. Human Thermoregulation
3. Thermoregulation and Microwaves
Perception
Simple models for temperature increase
Compartmental models and microwaves
(Combinations of 1 and 2)
II. RADIO FREQUENCY AND MICROWAVE ENERGY DEPOSITION
A. Earlier Models of Microwave Energy Absorption
The first model considered a semi-infinite plane of soft
tissue with high water content, such as muscle, with the
radiation hitting the air-tissue interface at a right angle.
Values for depth of penetration and percentage of absorbed
energy could be calculated readily from available dielectric
data. They were later confirmed experimentally.
As a next step, subcutaneous fat-muscle and then skin-
fat-muscle configurations exposed to radiation were consid
ered. Again the results could be readily predicted from
electromagnetic propagation theory and available dielectric
Microwaves and Thermoregulation 3
data. In this case spatial patterns of local energy absorp
tion (specific absorption rate, SAR) are more complex and
depend on frequency, as well as amounts of skin and fat. In
spite of the emerging complexity, it was possible to state
some rather general conclusions for most of the microwave
frequency range of dominant interest at that time:
1. Below 1 GHz, about 40% of the incident energy is ab
sorbed in the deeper situated muscle and core tissue,
and most of the other 60% is reflected.
2. Well above 3 GHz, the percentage of absorbed energy
increases slowly at first and then more rapidly from
about 40% to about 70%. This energy is almost
entirely absorbed in the skin.
3. Between these two extremes, the SAR distribution
depends critically on the thickness of the various
tissue layers and the frequency. The percentage of
total absorbed energy varies between 20% and 100%.
The conclusions from these studies have sometimes been
criticized since they were based on such simple models.
However, they can be expected to be applicable to partial
body irradiations, such as applied with diathermy techniques
and localized hyperthermia treatments. More recent work has
also demonstrated that these results are applicable to the
case of man's absorption of RF energy if appropriately
superimposed on man's resonance with the impinging field.
These earlier studies have been reviewed several times
(Schwan and Piersol, 1954; Schwan, 1965).
B. Cross-Section Studies
During the Fifties interest shifted from microwave dia
thermy to hazard problems. It therefore became necessary to
consider the absorption characteristics of the total man.
In the early Sixties we approximated man first by a homogen
eous tissue sphere and then by a tissue sphere surrounded by
a subcutaneous fat layer. Work was conducted both theore
tically and experimentally using a large anechoic chamber.
Techniques were developed to scale experimental data
obtained at one frequency to another frequency. This was
accomplished by using appropriately-sized manikins and
adjusting the conductivity of their interior saline solu
tions. The concept of the relative absorption cross-section
was introduced to express the ratio of total absorbed energy
to incident energy. It can readily be related to the con
cept of the body-averaged SAR (av.) and the total energy
absorbed E^_:
