Cardiovascular physiology

163 Pages·2007·10.92 MB·English

by  Pappano

Cardiovascular Physiology
A Text and E-Resource for Active Learning

Cardiovascular Physiology
A Text and E-Resource for Active Learning
Burt B. Hamrell
Emeritus Professor, Department of Molecular Physiology and Biophysics,
College of Medicine, University of Vermont, Burlington, Vermont
CRC Press
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Contents
Preface vii
Goals ix
SECTION I CARDIAC ELECTRO PHYSIOLOGY AND THE ELECTRO CARDIOGRAM (ECG) 1
1 Ventricular myocyte electrophysiology 3
Resting potential 3
Action potential 5
2 Cardiac electrical activity elsewhere than in ventricular muscle cells 9
Sinoatrial (SA) node 9
Atrial myocytes 11
Atrioventricular (AV) node 12
Bundle of His, bundle branches, and Purkinje myocytes 12
3 Physiological consequences of ionic mechanisms 15
Pacemaker hierarchy and latent pacemakers 15
Conduction velocity 16
Refractory period 17
Influence of extracellular K+ concentration on the transmembrane potential (V ) of ventricular
m
and atrial myocytes 19
4 Control of heart rate 21
Parasympathetic 21
Sympathetic 21
5 Electrical properties and cardiac myocyte structure 23
6 Conduction of electrical activity in the heart 25
Gap junction function 25
Conduction sequence in the heart 25
7 Electrocardiogram 29
Overview 29
ECG waves 30
Standard lead system 31
Monitoring leads 35
Frontal plane vectors 35
Mean electrical axis 41
Precordial leads 41
ECG patterns of normal and abnormal heart conduction 42
ECG patterns of abnormal rhythms: Arrhythmias 49
Mechanisms of arrhythmias 52
SECTION II CARDIOVASCULAR SYSTEM 59
8 How the circulation works 61
Blood pressure 61
Energy 61
Flow 62
v
Contents
Blood flow types 64
Blood flow velocity in the circulation 67
Clinical significance 67
9 Cardiac cycle, heart sounds, and murmurs 71
The circulation 71
Cardiac valves 71
Atrial and ventricular phases of the cardiac cycle 71
Normal intravascular pressures in people 75
Heart sounds 75
Murmurs during the cardiac cycle 78
10 Ventricular function 83
Preload 83
Contractility 85
Afterload 88
Examples of changes in ventricular function 90
Ejection fraction 91
Passive (diastolic) pressure-volume relation 91
Control of the heart in vivo: A study summary 93
11 Peripheral circulation 95
Mean arterial pressure and pulse pressure 95
Resistance 100
Blood volume distribution 103
12 Circulatory controls 105
Introduction 105
Arterial neural baroreceptors 105
Hormonal controls 109
Chemoreceptors 116
Local metabolic control 116
Autoregulation 117
Arterial blood pressure and salt and water metabolism 119
Veins in circulatory control 119
Blood pressure control, the autonomic nervous system, and heart failure 120
13 Regional blood flow 121
Introduction 121
Cerebral blood flow 121
Coronary blood flow 124
Skeletal muscle blood flow 129
Pulmonary blood flow 130
Renal blood flow 132
Gastrointestinal blood flow 132
Cutaneous blood flow 132
14 Microcirculation 135
Arterioles 135
Capillaries 135
Metarterioles 135
Postcapillary resistance 136
Nature of blood flow in the microcirculation 136
References for additional reading 143
Index 145
vi
Preface
The current emphasis in medical school teaching is on more active learning experiences in the
basic sciences. Teachers are being asked to tell less and facilitate more active student learning.
Students are being urged to reduce their expectation of being told what to learn and, instead,
to learn how to learn. Hopefully, learning then becomes a lifelong skill. Patients rarely have
symptoms and other findings as described in textbooks, they often respond differently than
uniquely to treatment, and treatment and disease information changes continually. A com-
petent physician cannot remain passive, but must actively pursue learning related to patient
problems. The competent physician continually actively learns and thinks.
Teachers are being urged to enhance their skills developing goals and objectives and struc-
turing student self-learning experiences. Student active learning source material often consists
of traditional resources such as instructor’s notes, textbooks or monographs, or current litera-
ture such as review articles. Used creatively, these materials can stimulate students to learn
how to learn. However, the electronic self-study modules presented here are not the traditional
material for discussion, but a learning resource that excites and engages the student learner.
Today’s student learners have grown up discovering information presented as electronic text,
images, animations, and videos. Fortunately, contemporary cardiovascular medicine is awash
with patient data presented as dynamic images, which can be configured, for instance, as ani-
mations that stimulate students to inform themselves and are optimally presented in an elec-
tronic format.
The electronic self-study modules presented here are active, self-learning, individually-
paced experiences. The text that follows serves as a reference source for the self-study modules.
The self-study modules include references to related parts of the text. The modules also include
frequent opportunities to choose to review concepts. Study question sets are included for self
assessment. The modules are designed to stimulate informal discussion among students and
are a superb vehicle for stimulating discussion in small group sessions. I use them in this way
in my teaching and they are uniformly successful.
The organization of the text and active learning modules follows the sequence of events in
each heartbeat. The electrophysiological basis of activation of the heart and the heart’s electrical
activity as manifest in the electrocardiogram are presented first. Then the discussion proceeds
to cardiac mechanical activity followed by the circulation of blood. The three-part self-study
module on cardiac muscle mechanics should be studied before learning about ventricular func-
tion. Likewise, it is important to learn about the cardiac cycle early on since the terminology
for describing pressures and flow is derived from the phases and events in the cardiac cycle.
The discussion of ventricular function precedes that of the peripheral circulation, circulatory
controls, and regional circulations. The text concludes with a discussion of the microcirculation
with emphasis on the dynamics of transcapillary fluid exchange and edema formation. The text
also refers the reader to relevant self-study module presentations and, as noted above, each
module cues the reader to relevant text material.
The self-study module on the pathophysiology of hypovolemic shock is included as a com-
pelling emergency clinical problem, the discussion of which provides an excellent review of
vii
Preface
most of cardiovascular physiology. Likewise, the discussion of chronic heart failure following
a myocardial infarction emphasizes the importance of using knowledge of the cardiac cycle,
cardiac muscle function, ventricular function, circulatory controls, and the physiology of the
peripheral circulation to help a patient.
Burt B. Hamrell
Westford, Vermont, 2016
viii
Goals
SECTION I CARDIAC ELECTRO PHYSIOLOGY AND THE
ELECTRO CARDIOGRAM (ECG)
After studying the self-study modules and referring to the text material you should be able to
discuss and explain the following:
• Characteristics of cardiac action potentials, including how ionic currents contribute to
each phase of the action potential.
• Why a ventricular cardiac action potential has a long duration and refractory period and
how that is an advantage for maintaining normal rhythmicity.
• Locations and ionic mechanisms of pacemaker function, and the role of neural and
humoral influences on pacemaker function.
• Normal sequence of cardiac activation and the role played by specialized muscle cells.
You should be able to discuss and explain the consequences of abnormal conduction at
any point in the sequence.
• Atrioventricular node function and its role in the sequence of conduction. You should
be able to discuss and explain the advantages of normal slow conduction through the
atrioventricular node and what factors determine the speed of conduction.
• Effects of sympathetic and parasympathetic activity on heart rate, conduction, and
cardiac excitation, and the ionic and other cellular mechanisms of these effects.
• Clinical usefulness of an ECG and how the usefulness is related to the use of a standard
electrode configuration, which you should be familiar with.
• Components of an ECG waveform and the relationship of the waves, intervals, and
segments to the simultaneous cellular electrical events occurring in the heart.
• What a dipole and vector are and how dipoles generated by the heart are reflected in the
ECG recording. Be able to discuss and explain ECG waveform configuration.
• Mean electrical axis of the heart and its clinical significance. You should be able to
estimate the direction of the mean electrical axis from frontal ECG lead recordings.
• Normal electrical conduction in the heart and the mechanisms of some conduction
defects and their ECG manifestations.
• Common arrhythmias and the mechanisms of how reentry and triggered activity can
cause arrhythmias.
SECTION II CARDIOVASCULAR SYSTEM
After studying the self-study modules and referring to the text material you should be able to
discuss and explain the following:
• How the blood normally circulates and some examples of abnormal blood flow. Discuss and
explain streamline and turbulent flow, why they occur and why they are clinically relevant.
ix