Peripheral Vascular Surgery. Tutorials in Postgraduate Medicine PDF
Preview Peripheral Vascular Surgery. Tutorials in Postgraduate Medicine
TUTORIALS IN POSTGRADUATE MEDICINE VOLUME THREE PERIPHERAL VASCULAR SURGERY Edited by MARTIN BIRNSTINGL, M.S., F.R.C.S. Consultant Surgeon, St. Bartholomew's Hospital, London Consultant Vascular Surgeon, Royal National Orthopaedic Hospital, London WILLIAM HEINEMANN MEDICAL BOOKS LTD L O N D ON First published 1973 © William Heinemann Medical Books Ltd 1973 ISBN Ο 433 02990 Ο Printed in Great Britain by C. Tinling & Co. Ltd, Prescot and London Preface This book has been written by a team of acknowledged experts, from personal and wide experience in their fields. The individual chapters stand on their own, but taken as a whole, the book aims to provide an up-to-date, authoritative introduction to peripheral vascular surgery. I hope that it will be useful for postgraduate surgeons, as well as providing a reference source for doctors in related fields, such as general medicine, cardio-thoracic and orthopaedic surgery. Most arterial and venous diseases now appear to be mainly the result, directly or indirectly, of mural deposition of solid material within a rapidly moving stream of blood. The vascular surgeon must therefore have a working knowledge of blood platelet interactions and probable mechanisms of thrombosis. He must also understand both the value and the limitations of present methods of blood flow measurement. The early chapters of this book throw a fresh and original light on these complexities and provide essential basic knowledge which may also prove valuable to surgeons and researchers already working in this field. Peripheral vascular surgery has now reached a stage where most of the purely technical problems have been resolved, but continuation of the original disease process often eventually defeats the surgeon's efforts. Further advances are likely to be due to better selection and clinical judgement, or in other words learning to choose the right operation for the right patient. This can only be achieved by continual long-term assess- ment of the results of the various procedures, and the surgeons who have contributed to this book have tried to emphasize the fundamental importance of this. I am very pleased to acknowledge the help given to me by the publishers, William Heinemann Medical Books Ltd, and in particular by Miss Ninetta Martyn. London August 1973 Martin Birnstingl vii List of Contributors A. K. BASU, M.S., F.R.C.S., F.A.C.S., F.A.M.S. Emeritus Professor of Surgery, Institute of Postgraduate Medical Education and Research, Calcutta 20 FRANK P. BELL, Ph.D. Lecturer, Department of Pathology, McMaster University, Hamilton, Ontario MARTIN BIRNSTINGL, M.S., F.R.C.S. Consultant Surgeon, St. Bartholomew's Hospital, London, E.C.I KENNETH BLOOR, M.D., Ch.M., F.R.C.S. Consultant Surgeon, The Royal Infirmary, Manchester NORMAN L. BROWSE, M.D., F.R.C.S. Professor of Vascular Surgery, St. Thomas's Hospital, London, S.E.I J. F. CADE, M.D., Ph.D., M.R.A.C.P. Assistant Professor, McMaster University, Hamilton, Ontario JOHN R. COBBETT, M.S., F.R.C.S. Consultant in Plastic Surgery, Royal Victoria Hospital, East Grinstead, Sussex H. H. G. EASTGOTT, M.S., F.R.C.S. Consultant Surgeon, St. Mary's Hospital, London, W.2 ix X LIST OF CONTRIBUTORS G. FARRER-BROWN, M.A., M.D. Senior Lecturer in Pathology, The Bland-Sutton Institute of Pathology, The Middlesex Hospital, London, W.l GEORGE FULFORD, M.S., F.R.C.S. Consultant Orthopaedic Surgeon, Western Infirmary, Glasgow JOHN D. HAMER, Ch.M., B.Sc, F.R.C.S. Lecturer in Surgery, Queen Elizabeth Hospital, Birmingham J. HIRSH, M.D., F.R.A.C.P. Professor, Departments of Pathology and Medicine, McMaster University, Hamilton, Ontario J. R. KENYON, M.S., F.R.C.S. Consultant Surgeon, St. Mary's Hospital, London, W.2 JOHN LUDBROOK, Ch.M., F.R.C.S., F.R.A.C.S. Professor of Surgery, University of Adelaide, Adelaide, 5000 ADRIAN MARSTON, M.A., D.M., M.Ch., F.R.C.S. Consultant Surgeon, The Middlesex Hospital, London, W. 1 DAVID NEGUS, D.M., F.R.C.S. Senior Surgical Registrar, St. Thomas's Hospital, London, S.E.I PAUL J. NESTEL, M.D., F.R.A.C.P. Department of Clinical Science, The John Curtin School of Medical Research, Australian National University, Canberra LIST OF CONTRIBUTORS XI KENNETH OWEN, M.S., F.R.C.S. Consultant in Urological Surgery, St. Mary's Hospital, London, W.2 COLIN J. SCHWARTZ, M.D., M.C.Path., F.R.C.P.A., M.R.A.C.P. Professor of Pathology, Faculty of Medicine, McMaster University, Hamilton, Ontario GEOFFREY SLANEY, Ch.M., F.R.C.S. Professor of Surgery, Queen Elizabeth Hospital, Birmingham SUSHILA SRIPAD, M.S. Cardiothoracic and Vascular Surgeon, Medical College Hospitals, Calcutta 12 G. W. TAYLOR, M.S., F.R.C.S. Professor of Surgery, St. Bartholomew's Hospital, London, E.C.I JOHN A. WALSH, M.D. Lecturer in Surgery, University of Adelaide, Adelaide, 5000 H. MALCOLM WHITE, D.Phil., F.R.C.P., F.R.A.C.P. Department of Clinical Science, The John Curtin School of Medical Research, Australian National University, Canberra Chapter Physiology One John Ludbrook and John A. Walsh It is impossible to practice peripheral vascular surgery without some knowledge of the factors that determine flow in blood vessels; of the inter-relationships between the vascular system and the volume of blood it contains; of the control systems that influence blood vessels; and of the techniques that can be used to make measurements of blood pressure, flow, and volume. The purpose of this chapter is to provide such an understanding, to suggest in what way physiologic mechanisms are relevant to disease states, and to indicate where further information can be sought. It should be pointed out that the account that follows is strictly human-oriented, and is based on data that has been gathered from study of the cardiovascular dynamics of man in health and disease, rather than that obtained from animal experiments. Because the subject of this book is peripheral vascular surgery, emphasis has been placed on the function of the peripheral vasculature. Nevertheless this chapter would be incomplete without a consideration of more general cardio- vascular functions. BIOPHYSICS OF BLOOD AND BLOOD VESSELS In the account that follows there has been a liberal interpretation of the term biophysics, to include all cardiovascular functions that are ful- filled mainly as a result of the physical properties of blood and blood vessels. It is becoming increasingly clear that the cardiovascular pheno- mena that attend a great many bodily activities are biophysically determined and that reflex action of the central nervous system, and tissue autoregulatory mechanisms merely add sublety and precision. The Determinants of Blood Flow Certain biophysical concepts in regard to blood and blood vessels are essential to the understanding of their biological functions. The treat- ment of these will be at a fairly non-mathematical level: more sophis- ticated information can be obtained elsewhere. 1 2 PERIPHERAL VASCULAR SURGERY The simplest description of the rate of volume-flow (QJ in a tube is as: "R where ΔΡ == the pressure difference between the ends of a tube, and R = the resistance to flow between these points. The Poiseuille equation is a more sophisticated description that was evolved to describe steady, laminar, flow of an ideal fluid in a straight, rigid, uniform-bore tube. In it, resistance (R) is described as ^JjH (where 77 r 4 r = tube radius, / = tube length, and η = viscosity of the fluid). Alternatively, flow may be described as the product of perfusion pressure and conductance, the latter being the reciprocal of resistance : ^ 8 1η Blood is no ordinary fluid, and blood vessels are not straight, rigid, nor of uniform bore. Nevertheless, the Poiseuille equation constitutes a useful starting point from which to consider the flow of blood in blood vessels. The Poiseuille equation describes laminar flow, in which the wave front is of a constant paraboloid form (Fig. 1.1). This description fits the flow of blood fairly accurately in most circumstances. However, the par- ticulate composition of blood results in one form of deviation from the ideal: there is a cell-free boundary layer adjacent to the vessel wall that LAMINAR FLOW PARABOLOID WAVE - FRONT FIG. 1.1 The paraboloid wave-front that is a feature of laminar arterial blood flow, and its distortion by transient turbulence at the origin of a branch. PHYSIOLOGY 3 assumes importance in small vessels (Fig. 1.6). Nor is blood flow laminar in all circumstances : in straight, uniform-bore tubes turbulent flow (Fig. 1.1) occurs when the Reynolds number (Re) exceeds a critical level, this number being a function of tube radius (r), velocity of flow (V), density of the fluid (p), and an inverse function of its viscosity (77). That is: In the normal vascular tree the Reynolds number rarely exceeds the critical level for turbulence except for brief periods of time and where the vascular geometry is complex (as at the aortic valve, or at the take-off of arterial branches). Only when there is pathologic irregularity, stenosis or dilation of an arterial lumen does prolonged turbulence occur. Among the consequences of turbulence is a sharp rise in energy-loss (and thus resistance to flow), and the production of audible murmurs that may be of diagnostic value. Finally, blood flow is pulsatile (rather than steady) in many blood vessels. This introduces a further complexity into the relation of pressure and flow, especially because of dynamic interaction with the visco-elastic arterial wall, and in regard to the production of turbulence. One effect of the elasticity of the central arteries is that at some points in the distal arterial tree flow may not be undirectional but is transiently reversed during cardiac diastole. This phenomenon is most apparent when peripheral resistance is high. Pressure. The actual, or measured, pressure at any point in the vas- culature is made up of hydraulic and hydrostatic components. Hydraulic Pressure is the force that drives blood through the vasculature (Fig. 1.2). This force is normally generated by cardiac action (although subsidiary musculovenous pumps contribute to hydraulic pressures in the venous system of the lower limb). In the arterial tree the hydraulic pressure is pulsatile, though for simplicity of analysis this driving force is often approximated to the mathematically-derived mean hydraulic pressure. The timing and shape of the hydraulic pressure waves that originate from the heart are considerably modified by the visco-elastic properties and geometric shape of the arterial tree (Fig. 1.3). The proximal aorta constitutes an elastic reservoir into which the left ven- tricular contents are discharged, and which dampens the central pressure pulse. Proceeding distally in the arterial tree the increasing rigidity of the vessel walls causes an exaggeration of the systolic peak and diastolic trough, of pressure. Arterial branching and the high resistance offered by the peripheral microvasculature cause reflection of pressure waves, so that at some points there is superposition of direct and reflected pressure peaks and troughs (standing waves). For the above reasons, at some points in the arterial tree distal-proximal pressure gradients may 4 PERIPHERAL VASCULAR SURGERY HYDRAULIC PRESSURE HYDROSTATIC PRESSURE ι 1 FIG. 1.2 Definitions of pressure. Hydraulic pressure gradients generated by the interaction of the cardiac pump with the resistance offered by arterial, microvascular, and venous elements of the vascular tree. Hydrostatic pressure in the venous system in the upright posture, result- ing from the weight of a column of blood in a system that is rendered "open-ended" by collapse of the veins above heart level. Transmural (distending) pressure: the difference between intravascular and tissue pressure. be transient (Fig. 1.3), and these account for the transient reversal of flow mentioned earlier. Nevertheless, there is a consistent downward gradient of mean pressure {hydraulic pressure gradient or ΔΡ) in the direction of mean blood-flow.
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