UTERINE BLOOD FLOW 



[605 



Case N 821 



mmHg 



minutes 



- 90 



10 



15 



20 



25 



30 



3T 



TD- 



TT 



To 



fig. 18. Effect of uterine contraction in women on maternal circulation. Uterine pressure is 

 shown on two sensitivity scales (0-100 mm Hg; 0-20 mm Hg to show effect of tonus in latter record 

 on vena cava pressures, superior vena cava, and retrohepatic). Note decrease in inferior caval pres- 

 sure as uterus contracts when tonus is high but not when tonus is low. Note bradycardia during 

 contraction. (Permission of Bieniarz el al., XXI Int. Cong. Physiol. Sciences, Buenos Aires, Aug. 

 '959-) 



the ewe, continuous monitoring; of uterine blood flow 

 in a uterine artery has been done with an electro- 

 magnetic flow meter. The third method involved in- 

 jection of radioactive sodium into the intervillous 

 spaces and measuring the disappearance rate. 



Metcalfe el al. (154) found by use of a modified 

 Fick principle (142) that the blood flow to the non- 

 gravid uterus in sheep and goats is 25 ml per min. 

 Slightly more than half way through pregnancy on 

 the 80th day, the flow increases to 200 ml per min. 

 At term, flow is more than 1 liter per min, a sub- 

 stantial increase in blood flow for an organ. The 

 surface area of the fetal portion of the human placenta, 



it may be noted parenthetically, is estimated to be 

 about 15 m 2 [Christoffersen (53)]; the increase in 

 placental villous surface area throughout pregnane} - 

 is described by Wilkin & Bursztein (245). 



Metcalfe et al. (153) have related the increase in 

 blood flow as observed by them and others to the 

 fetal demand, in the rabbit, human, and ungulate 

 (sheep, goat). The relations are summarized as 

 follows : 



