CHAPTER 3 



The volume of blood — a critical examination 

 of methods for its measurement 



HAMPDEN C. LAWS ONI 2 



Department of Physiology, University of Louisville 

 School of Medicine, Louisville, Kentucky 



CHAPTER CONTENTS 



Circulatory Mixing 



Correction for Loss of Label During Mixing Period 



Criteria of Uniform Mixing 



The Predicted Time Requirement for Mixing 



The Observed Mixing Time for Labeled Cells 



The Observed Mixing Time for Labeled Plasma 



Sequestration of Cells and Plasma 

 Distribution of Cells and Plasma in the Circulatory System 



Cell: Plasma Ratio of Drawn Blood 



The Error in Computing Cell Volume from Plasma Volume 

 and the Central Hematocrit 



The Mean Circulatory Hematocrit 



Local Circulatory Hematocrits 



Excess Plasma 



Anatomical Limits of the Plasma Compartment 

 Plasma Labels 



Evans Blue Dye, T-1824 



Other Dyes 



Plasma Proteins Labeled with Radioactive Tracers 

 Cell Labels 



Radioiron 



Radiophosphorus P^- 



Radiochromium 



Other Radioactive Labels 



THE CONCEPTUAL DEFINITION of blood volumc as the 

 volume of contents of the circulatory system (95) pro- 

 vides no clue to methods of quantitation. Herbst, in 

 1882, measured in animals the volume drained from 

 opened arteries under circulatory pressure, and found 



' Dr. Lawson died on June 23, 1961. 



^ The author's studies since 1957 have been aided by grant 

 No. H-3228 from the United States Public Heahh Service. 



it much less than the capacity of the system as esti- 

 mated by anatomical methods (see 149). The volume 

 obtained by bleeding to circulatory standstill, com- 

 monly called the bleeding volume, is now known to 

 represent something like one-half the blood volume 

 (138, 139, 235). In the hope of simply displacing the 

 residual blood to the exterior where it could be meas- 

 ured, Lehman and Weber in 1853, in their study of 

 two criminals sentenced to decapitation, washed out 

 the vessels with water after blood had ceased to flow, 

 and converted the total solids to a volume of blood. 

 There seems little doubt that solutes were added to 

 the washings by extraction of extravascular tissues, 

 since the blood volume estimated for one of the sub- 

 jects was 124 ml per kg (see 149). 



A washout of hemoglobin, as a specific blood con- 

 stituent, was introduced by Welcker in 1854 (see 64). 

 Although it is usually called the "direct method," it 

 is actually indirect for all other constituents than 

 hemoglobin. Calculation of plasma volume or of total 

 blood volume requires the assumption of a uniform 

 hemoglobin concentration throughout the vascular 

 system, an assumption which is shown later to be un- 

 warranted. Interchange with extravascular tissues 

 precludes the use of a washout procedure to obtain a 

 direct measurement of plasma volume, using any nor- 

 mal plasma constituent. 



The idea of an indirect approach to the measure- 

 ment of blood volume is usually credited to Valentin, 

 who in 1838 suggested that a known volume of dis- 

 tilled water be infused in living animals, the circu- 

 lating blood volume to be estimated from the resulting 

 dilution of total blood solids (see 64). The dilution 



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