Beschreibung
The hemodynamic significance of the flow properties of blood was put into perspective only during the past decade. Advances in modern technologies today allow the quantitative analy sis of the fluidity of blood and its components under conditions approximating the flow in vivo, particularly those in the microcirculation. The hematocrit is the most important of the determinants of blood fluidity (reciprocal value of blood viscosity); acute increases in the hematocrit exert deleterious effects on circulation and oxygen transport owing to impaired fluidity of blood. High viscosity of plasma due to hyper- or dysproteinemias initiates the microcirculatory dysfunctions in hyperviscosity syndromes. Furthermore, the fluidity or deformability of red cells might be critically diminished and therefore cause redistribution of blood elements and adversely affect the resistance to flow within the microvessels. In low flow states blood fluidity most likely becomes the key determinant for microvessel perfu sion, overriding the neural and local metabolic control mechanisms operative at physiological conditions to adjust blood supply to tissue demand. Microcirculatory disturbances are there fore encountered whenever driving pressures are reduced, as in shock or hypotension, and distal to stenoses of macrovessels, but also in hemoconcentration due to plasma volume con traction, polycythemia, leukemia, and dysproteinemia. Based on experimental studies exploring the possibilities and limitations, with regard to improving the fluidity of blood by reducing the hematocrit, the concept of intentional hemo dilution has been introduced to clinical medicine.
Autorenporträt
InhaltsangabeI Review of the Literature.- I Viscosity in General.- I.1 Introduction.- I.2 The Concept of Viscosity: Shear Stress and Shear Rate.- I.3 The Behavior of Viscosity: Newtonian and Non-Newtonian Fluids, Hemodilution and Defibrination.- I.4 The Fahraeus-Iindquist Phenomenon and the Inversion Phenomenon.- I.5 Plasma Skimming.- I.6 The Total Cross-Sectional Area of the Vascular Bed and the Flow Rate at Various Places in the Circulatory System.- I.7 The "Average Shear Rate" (4 v/r).- I.8 Internal Viscosity.- I.9 Exceptions to PoiseuilleâEuros Law: Laminar and Turbulent Flow and Rigid and Elastic Vascular Systems.- 1.10 Guyton's Equation of Circulatory Control.- II Viscosity in Relation to Cardiac Output, Blood Pressure and Peripheral Resistance.- II.1 Factors which Determine the Cardiac Output: The Relationship Between Cardiac Output and Viscosity.- II.1.1 Peripheral Factors.- II.1.1.1 Mean Circulatory Filling Pressure (Psf) Minus the Right Atrial Pressure ÂPra).- II.1.1.2 The Resistance to Venous Return.- II.1.2 Central Factors.- II.1.2.1 The Pumping Action of the Heart: Hypo- and Hyperactivity.- II.1.3 Equilibrium Values of Cardiac Output and Venous Return Under Normal Conditions.- II.2 Factors which Determine Blood Pressure: The Relationship Between Blood Pressure and Viscosity.- II.3 Factors which Determine Peripheral Resistance: The Relationship Between Peripheral Resistance and Viscosity.- III The Clinical Significance of Viscosity.- III. 1 Introduction.- III.2 Viscosity in the Postcapillary Venular Bed.- III.3 Relationship Between Hematocrit and Optimal O2-Transport Capacity at Varying Shear Rates.- III.4 High Viscosity Syndromes.- III.4.1 Myocardial Infarction, Angina Pectoris and Intermittent Claudication.- III.4.2 Cerebral Infarction.- III.4.3 Shock and Trauma.- III.4.4 Neoplasms.- III.4.5 Genetic Factors: Sickle-Cell Anemia.- III.4.6 Hormonal Factors: Diabetes Mellitus and Oral Contraceptives.- III.4.7 Pre-Eclampsia and Normal Pregnancy.- III.4.8 Toxic Factors: Cigarette Smoking and Alcohol.- III.4.9 Psychic Influences: Stress and Psychosis.- III.4.10 Hypo- and Hyperthermia.- IV Lowering the Viscosity with the Aid of Hemodilution.- IV.l Introduction.- IV.2 Physiological Consequences of Hemodilution.- IV.3 Clinical Applications.- IV.4 Criteria and Limitations.- IV.5 The Colloid Osmotic Pressure and the Colloid Hydrostatic Pressure Gradient.- IV.6 Comparison of Various Transfusion Fluids.- IV.7 Guidelines for Infusion in Case of Threats to the Circulation.- IV.8 Some Critical Remarks with Regard to Hemodilution.- V Lowering the Viscosity by Means of Defibrination with the Aid of Arvin.- V.1 Introduction.- V.2 Properties of Arvin.- V.3 Side Effects of Arvin.- V.4 Antidotes.- V.5 Indications.- V.6 Contraindications.- V.7 Treatment Schedules.- V8 Comparison of Arvin and Heparin.- V.9 Specific Action of Arvin.- V.9.1 The Cardiac Status.- V.9.2 The Microcirculation.- V.9.3 Deep Vein Thrombosis (DVT).- VI Viscometry.- VI.1 Introduction.- VI.2 Problems of Interpretation.- V1.3 Problems Related to the Measurement Techniques.- VI.4 Various Types of Measuring Apparatus.- VI.4.1 Capillary Viscometers.- VI.4.2 Rotation Viscometers.- VI.4.3 The Rheodeer Controlled Stress Rheometer.- VI.5 Alterations in Viscosity with Time, Due to the Factor Aggregation â< Disaggregation.- VI.6 Viscosity Parameters.- VI.7 Determination of the Yield Shear Stress.- VI.7.1 The Casson Plot Method (Extrapolation).- VI.7.2 The Torque Decay Method (Merill 1965).- VI.7.3 The Rheoscan Viscosity Curve (Humphreys 1975).- VI.8 Determination of the Asymptotic Viscosity.- VI.9 Artefacts in the Measurement Methods.- VI.10 Normal Values (in Man) with the Contraves LS 30 According to Humphreys.- II Material and Methods.- VII Material and Methods.- VII.1 General Remarks.- VII.1.1 The Experimental Animals.- VII.1.2 Anesthesia.- VII.1.3 Artificial Respiration.- VII.1.4 General Preparation.- VII.2 Specific Procedures.- VII.2.1 The Series with Extracorporeal Circulation (ECC)
