Table Of ContentBiomechanics of the Gastrointestinal Tract
Springer-Verlag London Ltd.
Hans Gregersen
Biomechanics of the
Gastrointestinal Tract
New Perspectives in Motility Research and Diagnostics
• Springer
Hans Gregersen, MD, DrMSci, MPM
Professor ofBioengineering, Centre for Sensory-Motor Interaction,
Laboratory for Gastrointestinal Biomechanics and Sensory-Motor Funtion,
Department of Surgical Gastroenterology, Aalborg Hospital, Aalborg University, Denmark
British Library Cataloguing in Publication Data
Gregersen, Hans
Biomechanics of the gastrointestinal tract : new perspectives in motility research and diagnostics
1. Gastrointestinal system - Motility
I. Tide
612.3'2
Library of Congress Cataloging-in-Publication Data
Gregersen, Hans, 1962-
Biomechanics of the gastrointestinal tract : new perspectives in motility research and
diagnostics 1 Hans Gregerson.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-84996-880-5 ISBN 978-1-4471-3742-9 (eBook)
DOI 10.1007/978-1-4471-3742-9
I. Gastrointestinal system-Mechanical properties I. Tide.
QP145 .G696 2002
612.3'2--dc21 2002029439
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Foreword
The alimentary canal is primarily a self-regulating mechanical device designed by
nature to move the liquids and solids taken in. It must move the heterogeneous food
materials in various complex ways to optimize the fermentation that constitutes
digestion, to provide the special flow patterns required for the absorption of the
nutrients that digestion releases, and to remove indigestible residue. It varies its oper
ations to adjust to the wide-ranging physical and chemical properties of the materials
presented to it. One must marvel at the fantastic ability of the gastrointestinal
machinery to do what it does.
Because of a deficient basis in theory, the motility of the gut was an empirically
realised process for a long time, largely incomprehensible and unpredictable. We now
possess a considerable mass of information about it from the application of new
methods in the reductionist strategies of modern biology. The resultant data describe
a vast array oflinked nonlinear processes in its neural and muscular apparatus. Their
interactions, however, still remain dimly perceived.
The movement of the gut continues to be perhaps the least rationally developed
subject in physiology. The regrettable consequence of this deficit lies in the promi
nence of disordered gastrointestinal neural and muscular function in medicine.
Disorders in this area constitute the root problem in most patients with alimentary
complaints. Virtually all oesophageal disease represents dysfunction in the nerves
and muscles of that organ. Diverticular disease of the colon, a common and vexing
problem in Western societies, also represents the consequence of gastrointestinal
neuromuscular dysfunction. Even diseases generally not thought to be of this nature,
such as gall bladder disease, involve disturbed mechanics.
The description of all mechanical devices involves two elements: the portrayal of
the mechanics and the analysis of the controlling systems. In the case of the
machinery of the gut, the mechanics seems to me to be especially neglected, for most
biologists in this area are largely unschooled in the physical sciences. Also, engineers
with the necessary skills rarely have the background necessary to deal with the
biological pro ces ses involved in the neuromuscular function of the gut. The new
discipline of biomechanics ought to be able to bridge the chasm in this and other
similar matters. It is for this reason that this book seems so welcome. I know of none
like it.
I fe ar that many readers from both sides of the divide will find this text tough going
simply because of the depth of their ignorance in the thought processes of the other
camp. Experience in this subject has taught me that true understanding requires not
v
vi Biomechanics of the Gastrointestinal Tract
just the reading of a text but daily conversations and discussions centred on specific
questions.
Such efforts seem warranted, however, for a keener understanding of the
mechanics of alimentation will surely benefit those who suffer from the mysterious
dis orders in the system that seem so common. From a better comprehension will
come better treatments and, perhaps, better ideas about the prevention of disease in
this system.
Also, it may offer new ideas in fluid mechanics. The engineer may welliearn many
usefullessons from a new awareness of the wondrous mechanism that evolution has
produced to allow the gut to manage its fluid contents.
farnes Christensen, Professor
Iowa City
Iowa, USA
Preface
Biomechanics and bioengineering are by now recognised research disciplines.
Though the gastrointestinal tract serves primarily a mechanical function,
biomechanics and bio engineering have only to a small degree entered the thinking
of researchers and clinicians in gastroenterology. Among the topics taught in
gastrointestinal physiology, mechanics receives litde attention. Graduates under
stand digestion, secretion, absorption, and hepatic functions, but they are unlikely
to answer questions about mechanics. Texts in physiology and medicine give insuffi
cient attention to the subject, yet many researchers in gastroenterology claim to
know biomechanical principles, which unfortunately leads to misuse of terms and
misinterpretation of assumptions and results. Biomechanical textbooks exist but
none of them focus on the gastrointestinal tract. For a long time I have felt the need
for a book that could be used to develop biomechanical ideas in gastroenterology
and to teach biomechanics and the application of mechanics to gastrointestinal
physiology and pathophysiology to the students and readers. The philosophy is that
a book is needed to show the power of the bioengineering approach to the gastroin
testinal research community. When these approaches have been adopted, the field
will bloom and there will so on be the need for an updated book. The book demon
strates how litde we know. We have to be open-minded in our search for
professional and valid scientific tools rather than to let conservatism and politics be
the main actors on the scene. The book presents my view of the current status and,
to a large extent, reviews my own work. A great deal is focused on the passive elastic
properties of gastrointestinal tissue. The rationale for this is that we need to under
stand the basic relations between stress and strain and the passive tissue properties
before we can interpret the active contractile behaviour. Future editions will focus
more on the integration of passive and active tissue properties. Many readers with
an interest in gastrointestinal motility and diagnostics of motor disorders will
undoubtedly find Chapter 5 about smooth muscle function and several other chap
ters interesting.
This book is not a comprehensive handbook of information about the selected
topics, neither does it give the complex mathematical and mechanical background.
The reader is referred to previously published work and to mechanics books to gain
the needed insight. This book as a whole outlines a basic overview ofbiomechanics as
it pertains to motility research in the gastrointestinal tract with minimal use of
complicated equations. The physiological and clinical importance of acquiring
biomechanical data, distensibility parameters, and interpretation of these results and
vii
viii Biomeehanics of the Gastrointestinal Traet
their associated errors are discussed. Some aspects of the relationship between
morphology, growth and biomechanics are discussed also. Chapter 2 provides the
essential knowledge of anatomy, morphology and physiology of the gastrointestinal
tract. The basic biomechanical theory is given in Chapter 3. Focus is on definitions of
terms, derivation of the appropriate equations and discussion of the assumptions for
the stress and strain computations. Methods and research tools are described in
Chapter 4 where a number of techniques to study the mechanical properties of the
gastrointestinal tract are outlined. The next chapter is devoted to gastrointestinal
smooth musc1e behaviour and mechanics. Recently, it was shown that residual
stresses and strains are prominent in the gastrointestinal tract, therefore, the whole of
Chapter 6 is aHocated to treating this phenomenon. The last two chapters of the book
present biomechanical data obtained in the gastrointestinal tract under normal
conditions as well as the remodelling and adaptation that occur in diseased tissue.
The work presented in this book would not have been possible without contribu
tions from my students, co-workers, collaborators, and mentors. I have received a
massive scientific input from the Bioengineering Institute at University of California,
San Diego. The coHaboration with Professor Emeritus Y.c. Fung, Professor Andrew
McCulloch, Professor Shu Chien, Professor Richard Skalak (deceased), S.Q. Liu, and
Wei Huang has been very inspiring. Associate research er Ghassan Kassab (now
Professor at UC Irvine) contributed to many projects at UCSD as weH as in Denmark.
I sincerely acknowledge his never-failing enthusiasm. Professor James Christensen
from University of Iowa Hospitals and Clinics is one of the few who recognise that we
must integrate gastroenterology with bio engineering. He has been a great inspiration
for many years. Many of the experiments mentioned in this book were performed by
my students and postdocs: Claus J0rgensen, Birgitte Duch, Gerda Villadsen,
Chunwen Gao, Jingbo Zhao, Xiao Lu, Klaus Krogh, Judd Day, James Smith, Jeff
Cassin, Yanling Dou, Yanhua Fan, Chunwen Gao, Jian Yang, Romulus Lontis and Liao
Donghua. Data are also presented from collaborative studies with the ultrasound
group in Bergen (in particular Dr. Odd Helge Gilja); Professor David Thompson and
Josephine Barlow, Hope Hospital, Salford; Professor Feng-Yuan Zhuang at the
Biomedical Institute at China-Japan Friendship Hospital in Beijing (now Chairman at
Beijing University of Aeronautics and Astronautics); and Professor Y.J. Zeng at
Beijing Polytechnic University. The Bioengineering Institute at the University of Cali
fornia, San Diego (1994-96), The Institute ofExperimental Clinical Research, Aarhus
University (1996-99), Aalborg Hospital and the Center for Sensory-Motor Interac
tion at Aalborg University (1999-2001) provided excellent working conditions during
the whole process. The collaboration with Professor Jens Christian Djurhuus, Dr.
Asbj0rn Drewes, and Professor Lars Arendt-Nielsen is appreciated. Karen Elise
Jensens Foundation, Ydes Foundation, The Danish Research Councils, and many
other foundations supported the work presented in this book.
I am specially indebted to Professor Y.C. Fung from University of California, San
Diego on whose work this book is based. He is truly considered the Father of
Bioengineering and has shown a number of students and readers ofhis literat ure the
way to follow. Professor Fung's books are classics and should be read by anyone inter
ested in biomechanics.
One of my obsessions is the science of gastrointestinal bio engineering and
biomechanics. It is my hope that this book can facilitate a better understanding of the
gastrointestinal tract as a biomechanical system and that an integrated approach can
help to understand those gastrointestinal disorders whose pathophysiology from a
bioengineering point of view hitherto has remained an enigma. I wish to address my
Preface ix
warrnest thanks to my most precious obsessions, my wife Lene and my children
Anne-Sofie (Fie) and Frederik for their support and care.
I also wish to thank Nick Mowat, Melissa Morton and Eva Senior from Springer
Verlag for their cooperation in producing this book.
August 2002
Hans Gregersen, Aalborg, Denmark
Contents
Chapter 1 The Concept ofBiomechanics................................... 1
1.1 Introduction .................................................... .
1.2 What is Biomechanics? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 History and Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 Applications of Biomechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4.1 Mechanoreceptors, Peristaltic Reflex and Sensory Function
Testing.... ....... ... .......... .. ...... ............ ...... .. 4
1.4.2 Smooth Muscle Tone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.3 Bolus Transport Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.4 Mechanical Forces, Growth, Remodeling and Morphology . . . . . . . 6
1.4.5 Clinical Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5 The Bioengineering Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 2 Geometry, Structure and Motor Function of the Gastrointestinal
Tract.................................................................... 11
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 The Structure and Composition of the Muscle Layers. . . . . . . . . . . . . . . . . . 12
2.2.1 The Main Muscle Coat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.2 The Muscle of the Mucosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2.3 Organ-specific Variations in the Muscle Layers . . . . . . . . . . . . . . . . . 13
2.3 The Structure and Composition ofthe Connective Tissue Layers...... .. 16
2.3.1 The Submucosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.2 The Subserosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.3 The Lamina Propria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.4 Organ-specific Variations in the Connective Tissue . . . . . . . . . . . . . 17
2.4 The Structure and Composition of the Epithelial Layers. . . . . . . . . . . . . . . . 20
2.4.1 The Gastrointestinal Epithelium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.2 The Serosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.3 Organ-specific Variations in the Epithelial Layers. . . . . . . . . . . . . . . 20
2.5 Intramural Nerves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.1 The Myenteric Plexus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.2 The Submucosal Plexus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.3 The Nerves of the Lamina Propria and Serosa. . . . . . . . . . . . . . . . . . 21
2.5.4 Organ-specific Variations in the Intramural Nerves. . . . . . . . . . . . . 22
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