OXYGEN UTILIZATION— ADOLPH 



47 



capillaries coiuluct blood in a tissue wliere it is used. The second factor depends 

 upon the operating characteristics of enzyme systems; they too transfer plenty of 

 oxygen at low temperature. 



The over-all delivery of oxygen from the blood to the tissues in general can be 

 estimated from analyses of mixed venous jjlood. Such analyses in anesthetized dogs 

 (Bigelow cf al., Rosenhain and Penrod. Hegnauer) show that the fraction of the 

 blood's oxygen that is unloaded at each circulation is about the same at 18° as at 38°. 

 Cooled tissues accumulate no measurable oxygen debt. 



Tissue pO >. So far as I am aware, partial pressures of oxygen have rarely been 

 measured by oxygen electrode in any tissue of hypothermic animals (Gollan, 1954). 

 Tissue p( ),. may be estimated liy two indirect methods, one based on oxygen content 

 of venous blood, the other based on pO^ of gas bubbles in body cavities. 1 lypothermic 

 venous blood in %'ii'o shows the diminished pO:- that would be expected from the 

 shift of oxygen dissociation. Analyses of subcutaneous gas bul)bles in rats (this 

 laboratory) also reveals the expected decrease of tissue pO^. 



Oxygen consumption of isolated tissues likewise diminished greatly (fig. 4). Rat 

 liver (Fuhrman and Field, 1943), brain (Field ct al., 1944), heart (Fuhrman ct al, 

 1950), and kidney (Fuhrman and Field, 1942) have been measured. Temperature 

 (juotients as well as thermal increments are fairly uniform in all ranges of tem- 

 perature. The limiting pO:., of air at which oxygen consumption would decrease in 

 slices of different tissues placed at various temperatures has not been ascertained; 

 this stud\- would tell us whether those tissues in vivo can be getting all the oxygen 

 they could use at the pOo prevailing there. 



Oxygen transfer in cells. iMnallv. the enzvmic transfer of oxvgen into carbon 



20 25 30 



TEMPERATURE "C. 



(5,^.-2.13 



10 IS 20 25 30 35 



TEMPERATURE "C, 



Fig. 4. — Oxygen cunsumptions (QO^) at various temperatures of brain slices from rats. 



From Field ct al. 



