Mechanisms of placentofetal blood flow

The average length of the umbilical cord at delivery is 21 +/- 1 in., but lengths vary from 10 to 50 in. When distended and carrying blood between the fetus and the placenta, the cord is longer; the distended areteries and vein are spiraled about each other. No physiologic data explain the manner by which blood flows from the placenta to fetus. When pressures (60-80 mmHg in arteries 10-20 mmHg in the vein) are recorded simultaneously, arterial pulse pressure has been observed to rise and umbilical vein pressure to fall. They are 180 degrees out of phase. When necessary physical factors are taken into account, it is found that the system satisfies all requirements of a pump known as one of the pulsometer type. This system is one that is widely used by engineers, but it is unique among physiologic systems.