HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



determined. The former give about lo per cent higher 

 blood volume values than do the latter (34). Correc- 

 tion for this deviation should therefore be made in a 

 comparison between the values. Generally, the carbon 

 mono.xide methods also give higher values than do the 

 blood cell methods using other labels. Most CO 

 determinations, however, are not sufficiently accurate 

 as to the volume of administered carbon monoxide, 

 and only with the alveolar CO method is the carbon 

 monoxide concentration in blood before administra- 

 tion of CO taken into consideration (54). Especially 

 in determinations in man, this inaccuracy may be the 

 cause of considerable errors. On the other hand, the 

 amount of CO taken up by the myoglobin is probably 

 not of such great significance as had earlier been 

 presumed. Values obtained with the alveolar CO 

 method in man fall, on the whole, between those found 

 with other blood cell and plasma methods (68, and 

 our own observations), and can, therefore, be directly 

 compared with these after correction for the deviation 

 of the body hematocrit from the hematocrit in the 

 analyzed blood. With due attention to these correc- 

 tions the abundant material published on blood 

 volume determinations under different conditions has 

 been used for an analysis of the variations and regula- 

 tion of the blood volume. 



Wniation in Blood Volume with Body Size 



In mammals — from the mouse to the horse — the 

 blood volume (BV/g) varies, on the whole, directly 

 with the body weight (b. wt. kg) according to the 

 regression equation i . 



BV = 0.055 b ^t- 0-99 



However, different animal species deviate more or 

 less from the blood volume values calculated from the 

 regression equation (see table i). Only to some extent 

 can these deviations be attributed to the use of differ- 

 ent methods of determination. Another reason for the 

 deviations could be that the blood volume varies 

 only indirectly with the total body weight but directly 

 with the mctabolically active body mass, atid that 

 the latter varies in different animal species in relation 

 to body weight. 



The blood vessel volume per volume of tissue varies 

 markedly from organ to organ. It is large for instance, 

 in the liver, kidneys, and spleen; small in adipose 

 and connective tissue. And so it is to be expected that 

 the blood volume per kg body weight should vary 

 according lo the Ijody's composition of different 



Comparable values have been selected from the literature 

 as far as possible. Except for horses, all values have been 

 obtained by plasma volume determinations. [For original 

 data and references see (11) and (20).] 



* Racing breeds. fWorking breeds. 



tissues and, particularly, inversely with that of adipose 

 tissue. The relationship of blood volume to theso-called 

 lean body mass was found to be essentially closer than 

 between blood volume and body weight only (48). 

 The adipose tissue too has some blood supply and 

 cannot therefore be ignored in this connection (42). 

 However, the blood volume in adipose tissue calcu- 

 lated by these authors seems too high. Blood volume 

 was also found to be constant in adults (49) in spite 

 of gain or loss of body weight. 



A closer analysis of the variation between different 

 species of mammals with respect to the relationship 

 of blood volume and blood cell volume, respectively, 

 to body weight shows that animals known for great 

 physical activity, as hares, dogs, and horses, have 

 both large blood volumes and large blood cell volumes 

 per kg body weight; and that physically inactive 

 animals, e.g., rats and rabbits, have small volumes. 

 The larger blood volume per kg body weight in the 

 physically active animals is not accompanied by a 

 higher basal metabolic rate. This is, therefore, prob- 

 ably explained by an adjustment of the vascular 

 system to the demand for a higher cardiac output, 

 that is, adjustment to temporary requirements of the 

 circulation rather than to changes in the basal circula- 

 tory demand. 



Observations in man also point in this same direc- 

 tion. If a comparison is made of the blood volume 

 per body weight ratios between different subjects 

 with different physical activity (individuals, for 

 instance, who are forced into extreme inactivity 

 because of a physical handicap — ordinarily active 

 women and men, and especially well-trained female 



