BLOOD VOLUME 



53 



TABLE 2. Blood Volume in Groups of Subjects Differing 

 in Physical Activity 



Blood volume values have been obtained by the alveolar 

 CO method under the same experimental conditions for the 

 different groups. The directly obtained values have been 

 corrected for the overestimation inherent in the CO method 

 and in the hemoglobin standard used. 



and male athletes) great differences will be found 

 (see table 2). For groups of people who are not selected 

 especially on the basis of body build, the height of the 

 body can be used as a reference value for the lean 

 body mass. It is therefore of interest that about the 

 same differences as those between the blood volume 

 per body weight ratios are noted if the blood volume 

 is compared to the body height. 



In view of this variability of the blood volume with 

 external circumstances, it is incorrect to give fixed 

 normal values and to compare these in different 

 subjects. The less physically active an individual is, 

 the more the blood volume approaches the minimum 

 necessary for maintenance of adequate circulation 

 (and, hence, adequate oxygen supph to the tissues 

 under conditions determined solely by endogenous 

 factors). Determinations in blind women, whose 

 handicap forced them into physical inactivity, indicate 

 that this level in humans would be a blood volume 

 somewhat below 60 ml per kg body weight. This 

 corresponds also to the lowest values in mammals, 

 that have been determined by means of comparable 

 techniques and calculations (45). Assuming that in 

 the blind the lean weight is 75 per cent of the body 

 weight, the "'basar' blood \olume per kg lean weight 

 would be about 70 ml. 



Variation with Body Type 



The blood \olume in man has been related to body 

 type, differentiated according to .Sheldon's system, 

 and certain variations have been observed (33). .Since 

 the adipose tissue also varies with body type, a closer 



evaluation of these observations is difficult. It is, 

 however, extremely probable that the size of the 

 vascular system in relation to the tissue supplied by it 

 is larger, the greater the body height, in other words, 

 the total volume of the vascular system varies with 

 the longitudinal dimension of the body. This concept 

 has also been supported by statistical analysis (3). 



Variation with Sex 



As regards the variation of the blood volume witli 

 sex, the published data differ. According to most 

 reports on such comparisons, men have a larger 

 blood volume per kg body weight than women; 

 according to others there is no significant sex differ- 

 ence. Any differences can be explained by different 

 external conditions, particularly as regards physical 

 activity. In dogs (10) and rats (29) there seems to be 

 no significant sex difference with respect to the blood 

 volume. The total blood cell volume, on the other 

 hand, is smaller in women as well as in the females of 

 other mammalian species generally. The difference 

 corresponds to the 10 per cent difference in hemato- 

 crit and the hemoglobin concentrations observed 

 between the sexes (23). This difference seems to be 

 associated with the influence of the sex hormones. 

 Thus, after castration, the difference disappears com- 

 pletely or almost completely (29). 



Variation with Age 



The blood \olume varies during body growth, 

 largely directly with age and commensurate to body 

 weight (44). After cessation of growth the blood 

 volume remains unchanged in the average human sub- 

 ject (55). The same seems to be true for the rat (60). 

 Since body weight in adults tends to increase with age 

 because of excessive development of fat, the blood 

 volume per kg of body weight decreases on the whole 

 linearly with age (55). In a subject that does not 

 show an increase of body weight with age this change, 

 as expected, is not obser\'ed (15). 



INTERNAL FACTORS THAT AFFECT BLOOD VOLUME 



Plasma I 'oliime/ Blood Cell \ 'olume Ratio 



Within certain limits the total blood volume 

 remains rather constant in spite of variations in the 

 plasma volume/cell volume ratio. With a marked 

 disturbance of this ratio the blood volume may 



