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Table 1.1 Why is cooperation difficult? The engineer’s view
Difficult medical terminology
Low precision in defining the requirements
Impatience
Little understanding of systematic work
Chaotic time management
Limited awareness of the significance of technical innovations
focus on BME problems since the majority expect to be provided with
innovative devices or methods by the industry and are not inclined to
take part in the development for themselves. Above all, the academic output of BME for surgeons is up to now low. Other fields of scientific
activities are far more interesting in regards to academic qualification,
such as oncology, transplantation, and so on. Fund raising is also far more
difficult than in other fields and a high number of impact factors can be
collected faster.
What can/should be done?
On the medical side, BME topics have to be integrated into the study
of medicine. The medical curriculum is continuously modified and new
topics such as gender are integrated. Accordingly, BME should become
also an obligatory part of the catalogue of learning objectives. Secondly,
attractive career prospects for BME qualified physicians have to be created
at the hospitals. The importance of BME has to be dissipated by the professional medical associations. Better means of academic credits have to
be introduced. It is not the primary task of a surgeon but he/she is able
to offer substantial contributions to BME:
• Identify and define the clinical need
• Critical support of the various stages of development
• Preclinical evaluation
• Clinical evaluation (proof of concept, application studies, randomized
controlled trials)
9Surgery and Biomedical Engineering
Table 1.2 Why is cooperation difficult? The surgeon’ s view
The industry should provide us with effective, innovative devices.
The engineers don’t need us. They prefer to do it alone.
Cooperation with engineers is tedious and takes a lot of time.
The academic output is low.
10 Biomedical Engineering in Gastrointestinal Surgery
The technical community has to become more active as well. It is
urgently needed that the profile of BME science should be defined more
clearly worldwide. Dedicated literature with high ranking journals and
well-accepted textbooks have to be created. Education and training has to
be standardized and has to be made transparent. BME lighthouses should
give an increased momentum to BME worldwide. Beyond that, much is
left for both sides to be done together. Interdisciplinary national and
international interest and lobby groups have to be established. Society and
politics have to be informed by regular public statements, most desirably
in an international frame. Much has already been done but the activities
have still to be intensified.
Conclusively, BME is still on the threshold of being perceived by the
academic community as an academic discipline of its own right. Due to
the rapid development of typical BME tasks and the distinct dependence
of interventional medicine—which is far more today than just conventional surgery—of technical innovations, medical doctors should have a
particular interest to contribute to make BME thrive.
BME as a new academic discipline should not attempt to monopolize
all types of BME. On the contrary, other disciplines like electrical or
mechanical engineering and many others should continue or even intensify their work on specific one-to-one issues with medical partners. As
soon as more systemic solutions are required, however, the expert in
BME should be involved. BME has to manage successfully the balancing
act of being brought to life as an offspring of various disciplines but being
nevertheless able to found its own entity. This is certainly difficult, but
the emerging of computer science which was originally coming both
from mathematics and electrical engineering is an example showing that
the goal can be reached.
REFERENCE
[1] Marcus HJ, Payne CJ, Hughes-Hallett A, Gras G, Leibrandt K, Nandi D, et al.
Making the leap: the translation of innovative surgical devices from the laboratory to
the operating room. Ann Surg 2016;263(6):10778.
CHAPTER 2
Anatomy, Physiology, and
Selected Pathologies of the
Gastrointestinal Tract
As seen from the biomedical engineering point of view, the anatomy and
even the physiology of the gastrointestinal tract are not too difficult to
understand. The task of this part of the body is the intake of food, transportation, resorption, and digestion, and finally defecation. It consists of
the esophagus, stomach, duodenum, small and large bowel. In addition,
the two important glands (liver and pancreas) have to be considered
(
Fig. 2.1).
The liver and pancreas can be understood as auxiliary but nevertheless
essential laboratories to process the substances which are taken up by the
GI tract and finally eliminated. Food is processed mechanically and chemically. Biomedical engineering (BME) concerns mainly the mechanical
aspects, although gray zones exist. Transportation is a major issue. In the
alimentary tract, straightforward transportation is as important as controlled regurgitation (retrograde movement). Sphincters serve as valves to
prevent retrograde flow. Some parts like the stomach or the rectosigmoid
serve for temporary storage.
Beyond the description of the necessary basic insights into human
anatomy and physiology, we make the attempt to delineate in this chapter
some urgent and up to now unsolved therapeutic problems which could
become an attractive field of BME activities.
Though medical treatment has contributed a lot to overcome gastrointestinal diseases without surgery (just to think of the introduction of
proton pump inhibitors) and will still contribute much more in the
future, there is still a lot to be expected from advances in operative
medicine based upon further impulses of BME. This ranges from a
further minimalization of the surgical access and the avoidance of collateral damage to the replacement of whole organs by artificial organs or
the implantation of pacemakers to modulate intestinal motility, etc.
Biomedical Engineering in Gastrointestinal Surgery. © 2017 Elsevier Inc.
All rights reserved.
11
12
Biomedical Engineering in Gastrointestinal Surgery
Figure 2.1 An overview of the viscerum: (A) Note: the pancreas is subtotally covered
by the stomach and the transverse part of the colon; (B) Illustration of the abdominal
viscera by Vesalius: De humani corporis fabrica libri septem 1543. From (A) M. Scholle,
(B) Courtesy: PD Dr. S. B. Reiser, Klinikum rechts der Isar.
2.1 THE GASTROINTESTINAL TRACT: AN OVERVIEW
The gastrointestinal tract can be compared with a coal power plant in its
organization. The “coal” (food) is delivered preprocessed, stored in an
intermediate place, finally transported to the furnace, then burnt and the
remnants are finally discarded.
The mouth, the teeth, and the esophagus are comparable to the
primary mill and to the transportation belt which deliver the substrate to
the intermediate store—the stomach. Here, food is stored in the upper
two thirds (receptive part). The distal third is characterized by intensive
motility activities (“antral mill”) which delivers the food in distinct
portions into the small bowel. Digestion occurs in the small intestine. In
the final part of the GI tract the feces are dehydrated and transported to
the rectosigmoid, where they are temporarily stored before it is decided
to empty it. All in all, food intake and digestion is a highly complex
process which, accordingly, is prone to a wide range of potential
malfunctions or damages.
In addition, various types of maldigestion or metabolic diseases occur,
but these are usually not the focus of BME. In the following, a brief
13Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
overview of the GI tract is given, together with some aspects of physiology and pathophysiology (the mechanism of diseases).
It is quite natural that a complicated mechanism like our coal power
plant and even more the human organism is prone to malfunctions.
Taking again this example, the problems can be classified as follows:
2.1.1 Structural Defects
Either parts of the construction are wrongly designed or the original
structure is altered during use.
In the GI tract, structural or anatomical defects occur as hernia
(bulging of the wall), diverticula (outpouching of the wall of the GI tract,
in particular in the esophagus or colon), obstruction (e.g., by adhesions),
or malpositions. Not all of them must be treated. If so, a surgical repair is
mostly required.
2.1.2 Functional Defects
If a transportation belt stands still, or if a valve does not open or close,
the workflow is severely impaired. In the human body, functional deficits
may also occur.
Transportation problems are known in the esophagus (achalasia), the
stomach, and the large bowel (constipation, diarrhea). Seldom, the small
intestine is involved as well. Most often, they are caused by innovation
failures.
At least three valves play a major role: The so-called upper esophageal
sphincter (usually opening problems leading to clinically significant swallowing problems—dysphagia), the lower esophageal sphincter between
esophagus and stomach (if it does not close properly, gastric acid flows
back into the esophagus and causes pain and erosions), and the anal
sphincter (causing constipation if it does not open properly or fecal
incontinency if it does not close).
2.1.3 Attrition and Erosion
Continuous use of a technical construction inevitably results in attrition
and aging which deteriorates the function and finally leads to a breakdown. This can be delayed by careful mending and immediate repair
when required, but no technical system can be designed for eternity.
Attrition and erosion (rust) contribute to this natural process.
14 Biomedical Engineering in Gastrointestinal Surgery
In the human body, attrition or aging affects the GI tract far less
intensively than the brain, or the bones and joints (osteoporosis, arthrosis),
or, just to name it, sexual function. With growing age, the colorectum
may slow down its function, leading to constipation, but in general, the
GI tract is rather resistant to aging.
The system is by far more endangered by two different hostile factors:
Bacterial or nonbacterial inflammation and cancer.
It may be surprising that bacterial inflammation is still a problem
today, so many decades after the detection of effective antibiotics.
Nonetheless, bacterial inflammation requires surgical intervention still
today, such as the inflammation of the gallbladder (cholecystitis) or the
sigmoid colon (diverticulitis).
Chronic noninfectious inflammation like Crohn’s disease may appear
within the whole GI tract, whereas ulcerative colitis is strictly confined to
the colon. In case of severe complications, they often require surgical
intervention.
The most clinically relevant disorder is cancer. In some regards, it can
be compared with rust in a steel construction. The best way to handle
the problem is prevention.
If rusting begins, it is extremely difficult to stop this destructive process. The construction loses functionality and finally it will break down
completely.
This is similar to cancer. It grows and infiltrates neighboring organs,
impairs them to deliver their natural functionality, and finally leads to the
complete breakdown of the system—death.
In opposition to the technical model of rust formation, cancer formation is accompanied by an additional feature: Cancer is able to create distant manifestations of the disease—so-called “metastases.” Cancer cells
migrate via blood circulation or lymphatic vessels to distant locations and
induce new tumor growth in distant regions.
Usually, they prefer the liver, the lungs, and the bones. Up to today, it
is poorly understood why these organs are primary targets. Abundant
blood perfusion cannot be the explanation, since some extremely well
perfused organs (heart, spleen) practically never develop manifest
metastases.
If cancer is detected at an early stage, it can be healed by surgical
resection. The more advanced it is, the more difficult it becomes to
achieve a cure. In order to describe malignant lesions more precisely, the
so-called TNM classification was developed.
15Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
T (tumor) describes the depth of invasion of the primary tumor. T1is
a very superficial type, whereas T
invaded neighboring organs. The range is from T
means that the tumor has already
4
to T4.
1
N (node for lymph node) describes whether lymph nodes are inflicted
or not. N
nodes, and N
means no lymph node infliction, N1is the infliction of nearby
0
of distant ones.
2
M (metastases) describes whether distant spread of cancer (metastases)
is present or not. M
M
) means no statement can be made.
X
means no presence of metastases. TX(or NXor
0
Often, additional letters such as a “G” for “grading” are used.
G defines the rate of growth of a malignant tumor. It ranges from G
(well differentiated, low grade) to G4(undifferentiated, high grade).
The individual constellations of the TNM classes are integrated into a
“stage.” Usually, four tumor stages are used, beginning with stage 0 (cancer cells present, but not yet infiltrating), stage I and II (tumor stages
which usually can be surgically removed), and the advanced stages III and
IV. Since a reliable and precise staging of malignant tumor is of outstanding importance for further improvement of therapy, the Union for
International Cancer Control implemented a process for continuous
improvement of the TNM classification systems. The modifications are
regularly published in new editions
[1].
Modern imaging provides a very precise insight into normal and pathological anatomy (
Fig. 2.2). CT or MRI scans create a 3D volume data set
which enables to visualize the topography of all sections of the GI tract.
As compared to former times, modern imaging procedures do show
not only static anatomical situations but also functional processes. Insofar,
they are superior not only to anatomical textbooks to get an insight into
normal anatomy but also to learn more about physiological activities.
1
2.2 ESOPHAGUS
2.2.1 Anatomical Description
The esophagus is the first part of the gastrointestinal tract as far as it concerns
gastrointestinal medicine. It begins at the end of the hypopharynx, at the
level of the sixth cervical vertebra (C6) at the height of the cricoid cartilage
(
Fig. 2.3), passes the chest behind the trachea and its bifurcation. Remaining
positioned above the spine, it enters the abdominal cavity through the
diaphragm at about the level of the tenth thoracic vertebra (T10) and ends
in the cardia—the transit zone between esophagus and stomach.
16
Biomedical Engineering in Gastrointestinal Surgery
Figure 2.2 MR Sellink of the abdomen: The abdomen in four coronary slices. The
small inserts (right side; bottom) indicate the height. (A) Coronary plane, a few cm
below the abdominal wall; (B) upper middle; (C) lower middle; (D) deep. (1) small
bowel; (2) liver; (3) urinary bladder; (4) right kidney; (5) descending colon; (6) spleen;
(7) spine column; (8) left femoral head; (9) rectum; (10) stomach; (11) ascending
colon; (12) transverse colon. Courtesy: Dr. K. Holzapfel, Klinikum rechts der Isar.
2.2.2 Functional Task
The primary function is the transportation of ingested food into the
stomach and the prevention of reflux. Two high pressure zones occlude
the esophagus which open only during swallowing: The upper (UES)
and the lower esophageal sphincter (LES). The function of the upper
high pressure zone is still poorly understood. It is assumed to create a
“second barrier” against reflux coming from the stomach.
Anatomy, Physiology, and Selected Pathologies of the Gastrointestinal Tract
Figure 2.3 The esophagus: The esophagus is a muscular hose which begins at the
so-called upper esophageal sphincter (“esophageal mouth”) and guarantees the
intestinal passage from the hypopharynx to the stomach. From M. Scholle.
17
The lower esophageal sphincter prevents gastric contents, in particular
acid, being regurgitated into the esophagus.
Since the esophageal mucosa (so-called squamous cell epithelium)
would be severely damaged by acid or other components of the gastric
content, the protective function of the LES is crucial.
Under resting conditions, both the UES and the LES are closed. If
the patient swallows, the ingested food (“bolus”) enters the esophagus
through the upper esophageal sphincter UES. The UES is actively opened
by relaxation and contraction of the respective muscles. As soon as the
bolus has passed, the sphincter is closed again and remains occluded until
the next act of swallowing is initiated.
The bolus is now advanced through the tubular esophagus to the
region of the esophagogastric junction. It is achieved by the strong muscle
wall of the esophagus with its circular and longitudinal layers. The contracted circular muscle segment is pulled down by the longitudinal muscle
layer in a strict sequence from oralad to caudad, resulting in a “peristaltic
wave.” As soon as the bolus comes close to the lower esophageal sphincter
18 Biomedical Engineering in Gastrointestinal Surgery
(LES), the LES relaxes enabling the transit into the stomach. After the
bolus passage, it closes again to prevent acid gastric reflux from the
stomach which may severely damage the esophageal mucosa.
2.2.3 Disorders and Diseases
The most frequent disorder is a decrease of resting pressure in the lower
esophageal sphincter resulting in pathological reflux. The regurgitation of
gastric content into the esophagus makes pain (“heartburn”) and causes
inflammation (“esophagitis”). In severe cases, bleeding, ulcers, or even
stenosis (narrowing of the esophageal lumen) may occur. Severe chronic
reflux favors the development of (Adeno-) carcinoma of the esophagus
(see
Section 2.2.4 Cancer). In most cases, medical treatment is sufficient.
In about 10% of cases, an interventional treatment is required.
The contrary is a missing opening reflex of the sphincter during
swallowing, leading to severe dysphagia (“achalasia”). The injection of
Botox is only temporarily helpful. The classical approach is either
dilatation or surgery (cardiomyotomy).
2.2.4 Cancer
Two types of cancer may occur: Squamous cell carcinoma arises on each
height of the esophagus. It is most often caused by heavy drinking and
concomitant smoking. Adenocarcinoma is induced by severe, chronic
reflux disease and obesity. Although squamous cell carcinoma predominates worldwide, Western nations have seen a marked rise in the
incidence of adenocarcinoma. Radical resection is the first therapeutic
choice, frequently accompanied by radio/chemotherapy. Esophageal
cancer surgery is highly demanding. Any further technical support would
be highly appreciated to make the intervention safer and simpler. Maybe
robotic surgery will become an option
[2].
2.2.5 Biomedical Engineering Aspects
Since gastroesophageal reflux is a very frequent disease and a very promising
market, artificial reinforcement of the lower esophageal sphincter is the
focus of many biomedical approaches. Several approaches are currently
being evaluated:
2.2.5.1 Internal (Endoscopic) Reinforcement
The history of endoscopic approaches to augment the sphincter is long.
During the past 15 years, a multitude of endoscopic therapies have