Reynolds S R
Obstet Gynecol. 1978 Feb;51(2):245-9.
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.
分娩时脐带的平均长度为21±1英寸，但长度范围在10至50英寸之间。当充盈并在胎儿与胎盘之间输送血液时，脐带会更长；充盈的动脉和静脉相互缠绕呈螺旋状。尚无生理学数据解释血液从胎盘流向胎儿的方式。同时记录压力（动脉为60 - 80 mmHg，静脉为10 - 20 mmHg）时，观察到动脉脉压升高而脐静脉压力下降。它们相位相差180度。考虑到必要的物理因素后发现，该系统满足一种被称为脉动计类型泵的所有要求。这种系统在工程师中广泛使用，但在生理系统中却很独特。
