VOLUME OF BLOOD 



4' 



from the gas tensions in alveolar air (8, 217). These 

 do not eliminate the basic defect which makes this 

 an unsuitable label for measuring the red cell volume. 

 It seems possible that the procedures may be modified, 

 with a longer mixing period, so as to obtain values 

 for the total body content of hemoglobin-like pig- 

 ments. 



It has long been known that blood carbon monoxide 

 concentration continues to fall for a considerable 

 period after its administration has been discontinued 

 (54). Only 60 to 70 per cent of the gas which disap- 

 pears from blood during the first hour is found in 

 expired air, although ultimately all of it is excreted in 

 this way (205). Whipple (239), suspecting an exchange 

 between circulating carbon monoxide hemoglobin 

 and the hemoglobin of muscle, extracted muscle 

 in dogs, and estimated that muscle hemoglobin 

 combined with 10 to 80 per cent as much of the gas 

 as did the hemoglobin of blood. This was a far greater 

 extravascular distribution of the gas, and a larger 

 and less constant error, than the 5 per cent estimate 

 of early investigators (107). The extravascular 

 accumulation of carbon monoxide in muscle has 

 been demonstrated in dogs by injecting Cr*'-tagged 

 cells at the time the gas is administered, and measur- 

 ing the activity of both labels in muscle tissue. The 

 ratio CO:Cr^' is consistently higher in muscle than 

 in blood (238). As would be expected, cell volume, 

 measured as the distribution volume of carbon mon- 

 oxide, is consistently larger than that measured with 

 more specific and firmly fixed cell labels (168, 171, 

 200). 



Cells may be labeled with methemoglobin by 

 treating drawn blood with nitrites (162), or with 

 Heinz granules by treating with phenylhydrazine 

 (169). Serologically identifiable untreated cells are 

 probably preferable (15, 19). Labeling with radio- 

 active tracers permits the choice of a fairly large 

 number of materials, some of which remain attached 

 to the cell for its life, and some of which are less 

 permanent. Some tracers may be introduced meta- 

 bolically in donors, others are incorporated in cells 

 in vitro, and thus permit the labeling of autologous 

 cells. Radioactive cell labels have superseded all 

 others for blood \olume studies. 



Radioiron 



Hahn et al. (102) observed in 1939 that when salts 

 of Fe^^ were fed to anemic dogs, the isotope became 

 concentrated in newly formed red cells. Cells labeled 

 in this manner in donor dogs were first used for cell 



volume studies in 1941 (104, 106). The use of donors 

 is imperative, as there is no Fe*' uptake by cells or 

 by hemoglobin solution in vitro (103). When the 

 procedure is employed in man, satisfactory labeling 

 of donor cells is achieved within about 3 weeks 

 following a single radioiron injection, even though 

 the donor is not anemic (84). The other radioisotope 

 of iron, Fe^^ with a much longer half-life, has also 

 been used (84). The two isotopes are readily distin- 

 guished by differences in type of radiation (181). 



The labeling of erythrocyte hemoglobin is perma- 

 nent, and persists for the life of the cell (76, 79). 

 Since the labeled cells are all freshly released young 

 cells, and since, if they are prepared in anemic 

 donors, they are also microcytic and hypochromic, 

 their distribution may not be typical of the whole 

 population of circulating cells (100). If blood incom- 

 patibilities are avoided, however, their distribution 

 space is the same as that of injected autologous cells 

 labeled with P^- (167). Anomalous data may be 

 obtained if incompatibilities exist between recipient 

 and donor. This seems to be a greater hazard in the 

 dog (100, 166) than in man (84), probably because 

 blood typing in man has been more thoroughly 

 studied and is technically simpler than in the dog 

 (108, 231). Even less is known for other species. 



Radtophosphorus P'- 



Hahn & Hevesy (105) introduced P^- as a cell 

 label in 1940. They first attempted to achieve firm 

 labeling of cells by tagging the phosphatids in 

 maturing erythrocytes in donor animals which received 

 NaHP^'-04, but found most of the P^'- in freely ex- 

 changeable acid-soluble forms. Although they conse- 

 quently abandoned this procedure in favor of in 

 vitro labeling of mature autologous cells (113), 

 phosphatid tagging of donor cells is sometimes done 

 when there is need for a more permanent label 

 (34, 179). Despite the rapid uptake of inorganic 

 P'- by the cells of drawn blood, it is released relatively 

 slowly when the cells are placed in inactive plasma 

 (10, 113, 128, 189). The difference in rate of P^- 

 ingress and egress is undoubtedly due to the fact 

 that its specific activity in plasma is high and in 

 cells low at the time when equilibrium is reached 



(113)- 



If, after incubation with P^'-, the cells are properly 

 washed before they are injected (36), the label 

 disappears from circulating blood at the average rate 

 of about 6 per cent per hour in man (194) and in the 

 unanesthetized dog (191). Neither barbital anesthesia 



