Theory and Practice of Blood Flow Measurement

276 Pages·1975·6.16 MB·English

by  John P. Woodcock (Auth.)

To my wife June
Theory and Practice
of Blood Flow
Measurement
JOHN P. WOODCOCK, M.Phil., Ph.D.
Welsh National School of Medicine and Department of Medical
Physics, University Hospital of Wales, Cardiff. Formerly Turner
and Newall post-doctoral Research Fellow of the University of
London, Department of Physics, Guy's Hospital Medical School
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First published 1975
© Butterworth & Co (Publishers) Ltd, 1975
ISBN 0 407 41280 8
Suggested UDC Number: 612· 13
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Cox & Wyman Ltd, London, Fakenham and Reading
Preface
This book is intended for hospital physicists, bioengineers, clinical
physiologists, surgeons and all who are interested in the measure-
ment of blood flow. The first section deals primarily with methods
for the measurement of blood flow in the major vessels, and the
second with the measurement of blood flow in organs and tissues.
The aim of the book is fourfold : first, to outline the theories under-
lying the various methods of flow measurement; second, to study
the performance of flowmeters which have been constructed in
accordance with these theories ; third, to study the practical applica-
tion in the measurement of blood flow; and fourth, to establish
normal values of blood flow in the organs and tissues of the body.
Throughout the book an attempt has been made to use SI units
or units compatible with the SI system. One example is the intro-
duction of the kilo-Pascal as the unit of pressure instead of mm Hg,
although both are used in this book; and whereas blood flow is
usually expressed as ml min_1/100 g tissue, ml min-11"1 tissue has
been used.
Acknowledgements
It is a pleasure to record my thanks to Professor P. N. T. Wells for
his interest and encouragement during the preparation of the book,
to Professor C. B. Allsopp, Emeritus Professor of Physics Applied
to Medicine, University of London, for my introduction to Medical
Physics, and to my many friends and colleagues at Guy's Hospital
for their interest and cooperation in various research programmes
which suggested the need for a book of this type.
JOHN P. WOODCOCK
Foreword
The physicists' association with haemodynamics has been a long
and fruitful one commencing with Robert Boyle, Robert Hooke
and Richard Lower, in the seventeenth century with their studies
of respiratory gas transport. Since the first measurement of circula-
tion time by Hering in 1829 and of phasic blood flow in blood
vessels by Volkmann in 1850, a whole range of physical measuring
techniques has been employed. These range from the calculation
of blood flow from the known dissipation of heat into the blood
stream, to the application of Faraday's law of electromagnetic
induction in the electromagnetic flowmeter, and Rayleigh's scatter-
ing theory for an understanding of the transcutaneous ultrasonic
flow velocity meter.
It is appropriate at this exciting stage in the development of blood
flow measuring instruments, when physicists and bioengineers are
more involved than ever before, that a critical assessment of the
capabilities of these instruments should be made. The accuracy,
calibration, frequency response and applicability of various tech-
niques to the variety of conditions met with in human blood flow
measurement are of great importance if reliable results are to be
obtained.
P. N. T. WELLS
Professor of Medical Physics,
Welsh National School of Medicine
SECTION ONE
Measurement of blood flow
in major vessels
This section is a review of techniques that have been used to study
blood flow in the major blood vessels, and includes indicator dilution
and thermal techniques, electromagnetic and ultrasonic flowmeters,
pressure sensing flowmeters, Ludwig stromuhrs and bubble flow-
meters, nuclear magnetic resonance, magnetorheography and a
radio-frequency (r.f.) coil system. The theory on which the instru-
ments are based is discussed, together with details of the calibration
procedure and potential hazards. Section II is a discussion of blood
flow measurement in the organs and tissues of the body—including
the brain, liver, kidney, limbs and limb segments, muscle, skin, adipose
tissue and bone. In the final chapter, the optimum characteristics
of the ideal flowmeter are discussed, and the attributes of each of
the types described are compared with the ideal instrument. In this
way it is hoped to be able to suggest the optimum flow measuring
technique to use in any specific case.
In arranging the subject content in this way it is inevitable that
techniques described in Section I can also be used in Section II to
study organ and tissue blood flow. In the chapter on thermal flow-
meters which, for convenience, is in Section I, the techniques of
calorimetry, conductivity and thermography are all used to measure
organ or tissue blood flows and should by rights be included in
Section II. However, it was felt that it is better to discuss flowmeters
which depend on either the production or detection of heat under
the one heading of thermal flowmeters and, as most of the thermal
flowmeters in routine use are used to measure flow in a major vessel,
it was decided to group these in Section I. The situation becomes
clearer when the tables of blood flow measurements in the normal
resting state are studied, because these show the techniques used
to make the measurements.
CHAPTER 1
Circulation of the blood
Empedocles of Agrigenti, as early as the sixth century B.C., contri-
buted the idea of the inter-relation between the pneuma or source
of health in the body, and the blood, which he considered to be the
carrier of innate heat, issuing from the heart and returning back to
it in a series of tides and pulsations (Sarton, 1952). Also in the sixth
century B.C. Alcmaeon of Croton distinguished two types of blood
vessel. In the Hippocratic Corpus (fifth century B.C.), the trachea
and bronchi were designated arteries because it was understood that
they transported the pneuma to the heart. Some blood vessels arising
from the heart cavity were found at death to contain air and to be
more or less empty of blood ; these were also designated arteries.
It is in this Hippocratic Corpus that the first suggestion that blood
circulates is found. It is said that the arteries also carried blood,
and connected with the veins, the blood being distributed to all the
body giving warmth and life. The movement of blood is compared
with the course of rivers returning to their sources after a passage
through numerous channels (Wiberg, 1937).
Herophylos (fourth century B.C.) considered that pulmonary
function was a four-stage process : first the absorption of fresh air,
second the distribution of air in the body, third the collection of
air returning from the body and, fourth, the evacuation of vitiated
air to the exterior. Erasistratos (fourth century B.C.) considered that
there were two separate systems for transporting air and blood.
First, the blood, the source of matter, nourished all the body.
Second, the pneuma, which consisted of the vital spirit and the
animal spirit, was the source of energy animating matter. In the
two transport system, blood was manufactured in the liver and
moved through the veins to all the organs. A small fraction reached
the right ventricle but was diverted because of the tricuspid valve
into the lungs for nourishment. Meanwhile air was inspired into the
lungs and flowed through the vein-like artery (pulmonary artery)
to the left ventricle. In the left ventricle it became vital spirit and
distributed to the body through the aorta and arteries. That part
of the vital spirit which reached the brain was converted to animal
3
4 CIRCULATION OF THE BLOOD
spirit and transported by means of hollow nerves to the entire body.
Erasistratos was the first person to recognize the undirectional flow
of blood to the lungs and of air to the left ventricle from the lungs.
Erasistratos also mentioned that the veins and arteries communi-
cated through fine vessels.
Galen (A.D. 130-201) further refined the ideas on the movement
of blood by introducing the concept of undirectional movement of
blood and air through the lungs. Up until Galen's time the venous,
arterial and nervous systems were considered to be completely
separate : the function of each was to distribute the natural, vital
and animal spirits throughout the body. Galen recognized that
blood was carried in both arteries and veins, otherwise the blood
would ebb and flow. Fleming (1955) stresses that Galen did not
advocate the ebb and flow of blood as is commonly understood,
but in fact explicitly stated that this was not the case. Although
Galen's contribution to the study of the circulation of the blood
is a very important one, there were two inconsistencies remaining.
First, he did not say that blood returned from the artery-like vein
(pulmonary vein) to the left ventricle. He maintained that inspired
air was carried to the left ventricle. When the pneuma was in the
left ventricle he further maintained that blood seeped through into
the left from the right ventricle when it became mixed to form the
vital spirit. This spiritous blood was then pumped around the body.
Second, when the inspired air reached the ventricle there was move-
ment of waste products in the opposite direction along the artery-like
vein (pulmonary vein).
This Galenic view of the circulation prevailed for 1400 years until
the time of Harvey (1578-1657), who disagreed with the theory of
bi-directional flow of air and waste products in the pulmonary vein.
He maintained that blood was forced out of the left ventricle and
distributed through the arteries to the whole body, and back through
the veins to the vena cava, then to the right auricle (atrium). From
the right auricle blood passed via the right ventricle and pulmonary
artery to the lungs and returned through the pulmonary vein to the
left auricle and left ventricle. Thus the circulation of the blood was
now established, although it was not understood how blood passed
from the pulmonary artery to the pulmonary vein until Malpighi
(1628-1694) described the pulmonary capillaries. Robert Boyle
(1627-1691) found that besides being cooled by air ventilated through
the lungs, the blood during its passage '. . . is disburdened of those
excrementitious steams proceeding for the most part from the super-
fluous serosities of the blood'. Richard Lower (1631-1691) noted
the difference in colour between arterial and venous blood and said
that the blood actually absorbs air in its passage through the lungs.
CIRCULATION OF THE BLOOD 5
Lavoisier (1743-1794) completed the basic understanding of the
circulation: The animal machine is governed by three main regu-
lating systems: respiration which consumes 0 and C0 , and
2 2
supplies the caloric; transpiration which increases or diminishes,
depending on whether it is necessary to eliminate more or less of
the caloric; finally, digestion, which returns to the blood what it
loses by respiration and transpiration.'
From the earliest times it was understood that blood played an
important part in the correct functioning of the body, providing
heat (Empedocles, sixth century B.C.) and 'life' (Hippocratic Corpus).
Harvey in Chapter XV of his work De motu cor dis (Leake translation)
maintains that as long as the heart is uninjured, life and health can
be restored to the body generally. He further says that it is no wonder
that many serious diseases gain access to the body, when it is suffering
from faulty nourishment and lack of normal warmth. It is at this
stage that it is appreciated that the circulation of the blood is of the
greatest importance for the maintenance of life. Harvey actually
calculated the amount of blood moved by the heart in one hour.
In Chapter IX of De motu cor dis he considers that if the heart pumps
1 oz of blood each beat and if it contracts about 1000 times in 0-5 h,
Quantities Weight of
of blood the blood Area of the• Area of the
equal to How sustained Number transverse transverse
The
the weight much in a by the left of pulses section of section of
several
of the minute ventricle in a descending' ascending
nnimnl^
lAlllffllAltJ animal in (lb) contract- minute aorta aorta
what time ing (in2) (in2)
(min) (lb)
Man 36-3 4-37 51-5 75
18-15 8-74
Horse 3d 60 13-75 113-22 36 0-677 0-369
Ox 88 1814 38 0-912 0-85
right left
Sheep 20 4-593 35-52 65 0094 007 0012
0-383 0-246
right left
Dog 1 11-9 4-34 33-61 97 0106 0041 0034
2 6-48 3-7 0102 0031 0009
3 7-8 2-3 19-8 0-07 0022 0009
4 6-2 1-85 111 0061 0015 0007
0119 0-7 0031
0125 0062 0031
7 6-56 419 0109 0053 0032
Fig. 1. Cardiac output of various animals, calculated by Stephen Hales and published
in Haemastaticks 1733 (From Fishman and Richards, 1964, by kind permission of
O UP, New York)
6 CIRCULATION OF THE BLOOD
then the heart pumps 83 lb 4 oz of blood, which is greater than the
total blood volume.
Stephen Hales (1677-1761) calculated the cardiac output of several
different animals (see Figure 1). In the case of the horse he filled the
left ventricle, after death, with warm beeswax which cooled and
solidified. He was thus, by removing the heart muscle, able to
calculate ventricular volume which in this instance was 160 ml.
Knowing the heart rate of the horse (36/min), Hales calculated the
cardiac output to be 61/min. In man, Hales estimated that the mass
of blood ejected at each systole was 2 oz, which is approximately
41 min"1 cardiac output.
The first measurement of circulation time was made by Hering
(1829) when he injected potassium ferrocyanide into the jugular vein
of a horse and detected it again at the jugular vein 30 s later, using
the Prussian blue reaction. Volkmann (1850), using a type of Ludwig
stromuhr, appears to have been the first to demonstrate the phasic
nature of flow in a blood vessel. Chauveau et al. (1860) constructed
an instrument which transferred the movement of a pendulum de-
flected by the blood stream, on to a kymograph for record purposes.
In 1867 the Ludwig stromuhrs, consisting of a l/-tube of known
volume, were used to measure blood volume flow. With each of
these flowmeters it was necessary to cannulate the blood vessel in
order to measure blood flow. Fick (1870) produced the first physio-
logical synthesis of the notions of blood flow and respiratory gas
transport in what is now known as the Fick Principle. The Fick
Principle states that cardiac output can be measured by knowing
the concentrations of oxygen or carbon dioxide in arterial and mixed
venous blood and the uptake of oxygen or release of carbon dioxide
by the lungs in a specified period of time, i.e. flow
r-8. 1
(C -C \
t A V
where Q is the uptake of oxygen by the lungs in time i, and C , C
A v
the arterial and venous concentrations of oxygen respectively. This
principle was not demonstrated experimentally until 1886 when
Grehant and Quinquard measured blood flow in dogs using this
technique. Whilst the application of the Fick Principle was a major
step forward, catheterization of blood vessels was still required. The
first instrument which could measure blood flow in a specific blood
vessel without invading the vessel was the thermostromuhr of Rein
(1928). The first instrument to measure blood velocity in a specific
vessel from the surface of the body was the Doppler-shift flow-
velocity meter invented by Satomura (1959).