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Physiological and clinical aspects of oxygenator design
Journal of Membrane Science, 4 (1978) 283-287 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
283
Book Reviews Physiological and Clinical Aspects of Oxygenator Design (Pmeediqs of the Seminar, Copenhagen, June 15-20,1975). Edited by S.G. Dawids and H.C. Engell, Elsevier Scientific Publishing Co., Amsterdam, 1976, xviii + 330 pp., ISBN O-444-41453-3, Dfl. 96.OO/US $ 39.25. This monograph is based on the proceedings of a seminar on “Advances in Oxygenator Design” held in Copenhagen, June 1975. It clearly presents the status of membrane oxygenator technology as it exists in Europe. The underlying purposes of the seminar, and consequently of the book, are threefold: “(1) to promote interdisciplinary contact between European Scientists working in the field of extracorporeal oxygenation; (2) to give a picture of the state-of-the-art; and (3) to give indications for the trends for future research.” The objectives are well met; however, proposed research areas could have been greatly expanded in the Introduction where the Editor briefly discusses past, present, and future advances in oxygenators. The vast majority of the twenty-seven papers are ex-viva studies of interest to the developmental engineer, and, although supported by clinical data, they are fundamentally design oriented and categorized into the following sections: Dimensional Conditions for Oxygenators, Oxygenator Construction, Experimental Methods of Oxygenation, Hematological Aspects, Tissue Factors, Measurements During Extracorporeal Circulation, and Compatibility Problems of Foreign Surfaces. One could summarize the central theme as optimizing gas exchange in devices using membranes, capillaries, and fluorocarbon fluids. Selected works which highlight the contents of this monograph follow. In the opening paper, Melrose addresses the major problems and outlines necessary design constraints such as oxygen consumption for various age groups at rest and during light exercise, oxygen and carbon dioxide dissociation curves, the influence of cardiac output and hematocrit on available oxygen, the relation between hematocrit value and absolute viscosity of normal blood, and the effect of shear rate on blood viscosity. He sets the task of blood oxygenation into a realistic context by aptly stating that “while we are not forced to imitate nature’s solution precisely, we are wholly constrained with limits set by the fluid we circulate, the tissues we perfuse, and the integration of the whole”. Spaan and Oomens emphasize the fact that gas transfer through a membrane into the blood will always be hampered by the diffusion process through the adjacent blood boundary layer. In oxygenators, where artificial mixing is provided, the boundary layer will be thin, but, in oxygenators without mixing, the rate of gas exchange through the membrane is directly dependent upon the diffusion process in this boundary layer. With the presentation of the above papers, a natural sequence is set for the remainder of the book where specific approaches are discussed. Monti’s work explores the possibility of solving some of the outstanding
284
fluid mechanics problems. He constructs dimensional analyses to evaluate the potential for making use of the convective blood oxygenator concept for exchanging oxygen between solution and blood and discusses the possible use of electromagnetic mixing to increase oxygen transfer by destroying the blood’s laminar boundary layer. The Taylor-Vortex membrane oxygenator is reviewed by Gaylor and Smeby with an empirical correlation for mass transfer based on experimental testing in a closed circuit. Oomens and Spaan combine their thoughts with those of Donders to discuss oxygen transfer analysis and scaling rules for annular membrane oxygenators with tangential flow. The study involves combining very thin blood layers with shear-induced blood mixing through the relative motion of two concentric cylindrical surfaces. A mathematical model of oxygen transfer having an adjustable effective diffusion coefficient for oxygen was used to analyze the oxygen uptake. Bellhouse and coworkers discuss the Oxford membrane oxygenator which works on the principle of accelerating and decelerating the flow of blood through channels to form vortices that provide efficient mixing for exchange of oxygen. Three series of experiments are presented, aimed at understanding the fluid mechanics of pulsatile flow over furrowed surfaces. An outstanding series of photographs are included which graphically display the existent flow patterns. Birnbaum’s paper sets forth the important advantages of microporous membrane material such as polytetrafluoroethylene for the so-called TefloLung. Further, he points out that tubular screens perform the function of contributing to gaseous exchange as well as serving as spacers between films and that the length of the blood passage must be optimized in an envelope oxygenator to minimize the interface and avoid increased pressure gradients. Mendler et al. utilize the principle of gas transfer between blood and a biologically inert fluid at a liquid-liquid interface for their studies. The oxygenator uses shear flow dispersion of blood in a fluorocarbon fluid to obviate membrane resistance to mass transport and the problems associated with direct contact of blood with gas. Strow et al. follow up on this basic concept by proposing the use of a supersaturated fluorocarbon in liquidliquid oxygenation. The advantage would be to increase the oxygen driving force with “little” damage to the blood. Two papers by Boe, Dawids and Jensen are presented. The first deals with the use of hyperbaric oxygen as a means of increasing the transfer rate to divided batches of blood. The other paper explores the use of hydrogen peroxide as an oxygen source for extracorporeal oxygenation. Hydrogen peroxide is a rich source of oxygen and can be used in water solutions with dialysis membranes. Care must be taken to avoid producing methemoglobinemia. This is accomplished by decomposing the peroxide before it contacts the blood. The high rate at which oxygen can be liberated in their scheme greatly reduces the necessary membrane area. The possible physiological effect of many of the aforementioned approaches are not disregarded. Schonbein, Rieger, and Zander study the behavior of erythrocytes subjected to high shear forces. They caution that
285
chemical agents can be liberated which can work together with physical, hormonal, thermal, and rheological factors to induce mechanical and/or viscous metamorphic injury to platelets. Therefore, shear forces must be minimized while optimizing gas exchange. A discussion by Lindsay of the roles played by platelets, foreign surfaces and heparin emphasizes that heParin has two antagonistic effects ~&Wmt t0 platelet/foreign surface interaction’ It acts &e&y On platelets in a manner to increase retention and acts on the foreign surface to reduce platelet retention. The latter is felt to be due to a competition for cationic platelet binding sites. He suggests that it is unlikely that heparin bonding confers reduced surface thrombogenicity by the “leaching off” process as has been proposed by others. Several short, valuable papers cover the effect of extracorporeal circuits on leucocytes and plasma Proteins, oxygen consumption at the cellular level, qualitative assessment of deposits on membranes, and measurement of blood gases. Agostoni provided two papers, one on the hemoglobin oxygen affinity for patients with acute myocardial infarction or angina pectoris, and the other on a computer-operated system for the evaluation of extracorporeal oxygenators. In the latter, he describes the control systems for blood gas measurement, peristaltic pump rate, heparin infusion, and sample acquisition along with appropriate algorithms. Kimmich and Kreuzer review the shunt method and the direct method of measuring arterial PO2 during prolonged clinical use with a catheter electrode placed in a central or peripheral vessel. Reliable measurements seem to depend upon how well one services and applies the PO2 transducers. Lenssen et al. describe automatically operated perfusion systems which regulate oxygen and carbon dioxide with changes in PO, and PCOZ. The relationship of pulmonary mechanics, hemodynamics, and gas exchange to the physiological condition occurring during extracorporeal circulation is reported by Lemaire and coworkers. The last four papers are on biomedical materials with emphasis on membrane composition and construction in the form of an overview. Haworth outlines the necessary criteria for selecting biomaterials, and Lagergren briefly reviews the various approaches taken in the past to lend antithrombogenicity to surfaces. Pusineri describes a process called +zing*’ which is reported to add smoothness to the surface of silicone rubber to minimize the formation of thrombi at the blood-prosthesis interface. Feyen Presents a sketchy report on a water soluble polyelectrolyte that renders PVC and Silastic* “non-thrombogenic” . Pertinent details on specific composition and physical/chemical properties that would be of interest to the materials-oriented engineer are not presented. Despite a few weaknesses, the book represents an excellent resource and should be within easy reach of all those involved in oxygenator development. when coupled with the proceedings* of a similar meeting of representatives *Artificial Lungs for Acute Respiratory
Elsevier,N.Y., 1976,557 pp.
Failure. Edited by WM. Zap01 and 3. Qvist,
286
of other countries, including the United States, held at the same time and place, it provides a comprehensive review. J.W.BORETOS National Institutes of Health Bethesda, Maryland
Vol. 1. Wastewater Treatment and Separation Methods. R.P. Ouellette, J.A. King and P.N. Cheremisinoff, Editors, Ann Arbor Science, Ann Arbor, Michigan, 1978,609 pp,, E 25.20/$ 43.95.
Ebctrotechnology.
This book consists of twelve chapters dealing with various wastewater treatment and separation methods. Five of the chapters, representing approximately one-third of the book, deal with membrane processes: ultrafiltration (UF), reverse osmosis (RO), and electrodialysis. The remaining chapters deal with topics such as electrolysis, electrochemical recovery of metals, electromagnetic separation of solids, ozone effluent treatment, and water disinfection, The applications, markets, and economics of these processes are stressed. The treatment of process principles is brief. This type of review can be useful. In the UF and RO areas, for example, most of the published literature is written by proponents of one or another of the competing membrane systems, each with his own particular axe to grind. An independent analysis has been needed for some time, Unfortunately, this book does not provide the analysis required, inasmuch as the authors of the membrane chapters in this book are not membrane specialists and, consequently, the chapters contain imbalances. The book contains many useful tables culled from a variety of sources and will provide a useful introduction to this subject for the new student. However, the book does not have the perspective to satisfy more knowledgeable readers. R.W.BAKER Bend Research, Inc., Bend, Oregon
in Life Sciences. Structural and Kinetic Approach to Plasma Membrane Functions. Proceedings of a meeting held on September 6-9,
Proceedings
1976 in Grignon, France. Edited by C. Nicolau and A. Paraf, SpringerVerlag, Berlin, 1977, $ 25.60 The book contains 13 lectures which were given at a symposium in Grignon. The meeting brought together physicists, physicochemists, biochemists, and biologists for the exchange of knowledge about membrane structure and
283
Book Reviews Physiological and Clinical Aspects of Oxygenator Design (Pmeediqs of the Seminar, Copenhagen, June 15-20,1975). Edited by S.G. Dawids and H.C. Engell, Elsevier Scientific Publishing Co., Amsterdam, 1976, xviii + 330 pp., ISBN O-444-41453-3, Dfl. 96.OO/US $ 39.25. This monograph is based on the proceedings of a seminar on “Advances in Oxygenator Design” held in Copenhagen, June 1975. It clearly presents the status of membrane oxygenator technology as it exists in Europe. The underlying purposes of the seminar, and consequently of the book, are threefold: “(1) to promote interdisciplinary contact between European Scientists working in the field of extracorporeal oxygenation; (2) to give a picture of the state-of-the-art; and (3) to give indications for the trends for future research.” The objectives are well met; however, proposed research areas could have been greatly expanded in the Introduction where the Editor briefly discusses past, present, and future advances in oxygenators. The vast majority of the twenty-seven papers are ex-viva studies of interest to the developmental engineer, and, although supported by clinical data, they are fundamentally design oriented and categorized into the following sections: Dimensional Conditions for Oxygenators, Oxygenator Construction, Experimental Methods of Oxygenation, Hematological Aspects, Tissue Factors, Measurements During Extracorporeal Circulation, and Compatibility Problems of Foreign Surfaces. One could summarize the central theme as optimizing gas exchange in devices using membranes, capillaries, and fluorocarbon fluids. Selected works which highlight the contents of this monograph follow. In the opening paper, Melrose addresses the major problems and outlines necessary design constraints such as oxygen consumption for various age groups at rest and during light exercise, oxygen and carbon dioxide dissociation curves, the influence of cardiac output and hematocrit on available oxygen, the relation between hematocrit value and absolute viscosity of normal blood, and the effect of shear rate on blood viscosity. He sets the task of blood oxygenation into a realistic context by aptly stating that “while we are not forced to imitate nature’s solution precisely, we are wholly constrained with limits set by the fluid we circulate, the tissues we perfuse, and the integration of the whole”. Spaan and Oomens emphasize the fact that gas transfer through a membrane into the blood will always be hampered by the diffusion process through the adjacent blood boundary layer. In oxygenators, where artificial mixing is provided, the boundary layer will be thin, but, in oxygenators without mixing, the rate of gas exchange through the membrane is directly dependent upon the diffusion process in this boundary layer. With the presentation of the above papers, a natural sequence is set for the remainder of the book where specific approaches are discussed. Monti’s work explores the possibility of solving some of the outstanding
284
fluid mechanics problems. He constructs dimensional analyses to evaluate the potential for making use of the convective blood oxygenator concept for exchanging oxygen between solution and blood and discusses the possible use of electromagnetic mixing to increase oxygen transfer by destroying the blood’s laminar boundary layer. The Taylor-Vortex membrane oxygenator is reviewed by Gaylor and Smeby with an empirical correlation for mass transfer based on experimental testing in a closed circuit. Oomens and Spaan combine their thoughts with those of Donders to discuss oxygen transfer analysis and scaling rules for annular membrane oxygenators with tangential flow. The study involves combining very thin blood layers with shear-induced blood mixing through the relative motion of two concentric cylindrical surfaces. A mathematical model of oxygen transfer having an adjustable effective diffusion coefficient for oxygen was used to analyze the oxygen uptake. Bellhouse and coworkers discuss the Oxford membrane oxygenator which works on the principle of accelerating and decelerating the flow of blood through channels to form vortices that provide efficient mixing for exchange of oxygen. Three series of experiments are presented, aimed at understanding the fluid mechanics of pulsatile flow over furrowed surfaces. An outstanding series of photographs are included which graphically display the existent flow patterns. Birnbaum’s paper sets forth the important advantages of microporous membrane material such as polytetrafluoroethylene for the so-called TefloLung. Further, he points out that tubular screens perform the function of contributing to gaseous exchange as well as serving as spacers between films and that the length of the blood passage must be optimized in an envelope oxygenator to minimize the interface and avoid increased pressure gradients. Mendler et al. utilize the principle of gas transfer between blood and a biologically inert fluid at a liquid-liquid interface for their studies. The oxygenator uses shear flow dispersion of blood in a fluorocarbon fluid to obviate membrane resistance to mass transport and the problems associated with direct contact of blood with gas. Strow et al. follow up on this basic concept by proposing the use of a supersaturated fluorocarbon in liquidliquid oxygenation. The advantage would be to increase the oxygen driving force with “little” damage to the blood. Two papers by Boe, Dawids and Jensen are presented. The first deals with the use of hyperbaric oxygen as a means of increasing the transfer rate to divided batches of blood. The other paper explores the use of hydrogen peroxide as an oxygen source for extracorporeal oxygenation. Hydrogen peroxide is a rich source of oxygen and can be used in water solutions with dialysis membranes. Care must be taken to avoid producing methemoglobinemia. This is accomplished by decomposing the peroxide before it contacts the blood. The high rate at which oxygen can be liberated in their scheme greatly reduces the necessary membrane area. The possible physiological effect of many of the aforementioned approaches are not disregarded. Schonbein, Rieger, and Zander study the behavior of erythrocytes subjected to high shear forces. They caution that
285
chemical agents can be liberated which can work together with physical, hormonal, thermal, and rheological factors to induce mechanical and/or viscous metamorphic injury to platelets. Therefore, shear forces must be minimized while optimizing gas exchange. A discussion by Lindsay of the roles played by platelets, foreign surfaces and heparin emphasizes that heParin has two antagonistic effects ~&Wmt t0 platelet/foreign surface interaction’ It acts &e&y On platelets in a manner to increase retention and acts on the foreign surface to reduce platelet retention. The latter is felt to be due to a competition for cationic platelet binding sites. He suggests that it is unlikely that heparin bonding confers reduced surface thrombogenicity by the “leaching off” process as has been proposed by others. Several short, valuable papers cover the effect of extracorporeal circuits on leucocytes and plasma Proteins, oxygen consumption at the cellular level, qualitative assessment of deposits on membranes, and measurement of blood gases. Agostoni provided two papers, one on the hemoglobin oxygen affinity for patients with acute myocardial infarction or angina pectoris, and the other on a computer-operated system for the evaluation of extracorporeal oxygenators. In the latter, he describes the control systems for blood gas measurement, peristaltic pump rate, heparin infusion, and sample acquisition along with appropriate algorithms. Kimmich and Kreuzer review the shunt method and the direct method of measuring arterial PO2 during prolonged clinical use with a catheter electrode placed in a central or peripheral vessel. Reliable measurements seem to depend upon how well one services and applies the PO2 transducers. Lenssen et al. describe automatically operated perfusion systems which regulate oxygen and carbon dioxide with changes in PO, and PCOZ. The relationship of pulmonary mechanics, hemodynamics, and gas exchange to the physiological condition occurring during extracorporeal circulation is reported by Lemaire and coworkers. The last four papers are on biomedical materials with emphasis on membrane composition and construction in the form of an overview. Haworth outlines the necessary criteria for selecting biomaterials, and Lagergren briefly reviews the various approaches taken in the past to lend antithrombogenicity to surfaces. Pusineri describes a process called +zing*’ which is reported to add smoothness to the surface of silicone rubber to minimize the formation of thrombi at the blood-prosthesis interface. Feyen Presents a sketchy report on a water soluble polyelectrolyte that renders PVC and Silastic* “non-thrombogenic” . Pertinent details on specific composition and physical/chemical properties that would be of interest to the materials-oriented engineer are not presented. Despite a few weaknesses, the book represents an excellent resource and should be within easy reach of all those involved in oxygenator development. when coupled with the proceedings* of a similar meeting of representatives *Artificial Lungs for Acute Respiratory
Elsevier,N.Y., 1976,557 pp.
Failure. Edited by WM. Zap01 and 3. Qvist,
286
of other countries, including the United States, held at the same time and place, it provides a comprehensive review. J.W.BORETOS National Institutes of Health Bethesda, Maryland
Vol. 1. Wastewater Treatment and Separation Methods. R.P. Ouellette, J.A. King and P.N. Cheremisinoff, Editors, Ann Arbor Science, Ann Arbor, Michigan, 1978,609 pp,, E 25.20/$ 43.95.
Ebctrotechnology.
This book consists of twelve chapters dealing with various wastewater treatment and separation methods. Five of the chapters, representing approximately one-third of the book, deal with membrane processes: ultrafiltration (UF), reverse osmosis (RO), and electrodialysis. The remaining chapters deal with topics such as electrolysis, electrochemical recovery of metals, electromagnetic separation of solids, ozone effluent treatment, and water disinfection, The applications, markets, and economics of these processes are stressed. The treatment of process principles is brief. This type of review can be useful. In the UF and RO areas, for example, most of the published literature is written by proponents of one or another of the competing membrane systems, each with his own particular axe to grind. An independent analysis has been needed for some time, Unfortunately, this book does not provide the analysis required, inasmuch as the authors of the membrane chapters in this book are not membrane specialists and, consequently, the chapters contain imbalances. The book contains many useful tables culled from a variety of sources and will provide a useful introduction to this subject for the new student. However, the book does not have the perspective to satisfy more knowledgeable readers. R.W.BAKER Bend Research, Inc., Bend, Oregon
in Life Sciences. Structural and Kinetic Approach to Plasma Membrane Functions. Proceedings of a meeting held on September 6-9,
Proceedings
1976 in Grignon, France. Edited by C. Nicolau and A. Paraf, SpringerVerlag, Berlin, 1977, $ 25.60 The book contains 13 lectures which were given at a symposium in Grignon. The meeting brought together physicists, physicochemists, biochemists, and biologists for the exchange of knowledge about membrane structure and