34 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



Table 1-6. Calculation of Tkanscapillary Exchange of Na 



[From Alfred Gellhorn, Margaret Merrell, and Robert M. Rankin, The Rate of 

 Transcapillary Exchange of Sodium in Normal and Shocked Dogs, Am. J. Physiol., 

 142: 407-427 (1944).] 



curve A. The intercept and slope of this Hne give values of 2117 and 

 1.040, respectively, Ui and 6i. The equation for this process is then 



r - 1000 = 2117e-> 04°' + OSSe-o-o^^' 



(1-32) 



It must be remembered that the constants in Eq. (1-32) refer to the 

 behavior of labeled sodium ions introduced into the plasma, and since the 

 primary interest is in the behavior of sodium ions in the plasma, it is 

 necessary to make conversions: 



1. The initial plasma concentration of labeled Na ions = 



Ceg + ai + aa = 4050. 



2. (Na in plasma) /(total Na) = C/Co = 0.247. 



3. Percentage of Na in plasma transferred per minute from plasma to 

 extra vascular fluid, Rp = (aibi + a2b2)/Co X 100 = 56.6. 



4. Percentage of Na in total body transferred per minute from plasma to 

 extravascular fluid, Rt = RpCeg/Co = 14.0. 



