Modern textbooks of cardiology 1,2 ascribe a major role to an increase in blood volume to explain the pathogenesis of the signs and symptoms of congestive cardiac failure. This concept has been challenged by the observations of Prentice et al.3 and of Ross and his co-workers,4,5 who used P32-labeled erythrocytes instead of Evans blue dye to measure the blood volume in patients with congestive cardiac failure and in dogs in which congestive cardiac failure had been produced by experimental means.
Part of the difficulty may lie in the use of the ambiguous phrase "blood volume." The term "blood volume" is employed to designate the anatomical compartment bounded by the endothelial cells of the vascular system, i. e., the actual physical space enclosed within the heart and the arterial, capillary, and venous vessels. We have chosen the term "intravascular volume" to denote this physical space. The methods