Uteroplacental Circuit

This is, probably, the only blood circuit of a pregnant and delivering uterus, physiology of which has been rather sufficiently studied. Both arterial and venous links, as well as intervillous space do not possess the ability to selfregulate the intensity of uteroplacental bloodflow. Intramyometric and intraamniotic tensions are the factors of its external regulation. Resistance of bloodflow in circuit is defined by intramyometric (myometric parts of uteroplacental arteries and veins) and amniotic tension (decidual parts of uteroplacental arteries and veins and intervillous space). In our published works we have observed those pieces of work that studied human and primates’ issue of regulation and physiology of uteroplacental flow from different perspectives (radiotracers, contrast radiokinography, coloring agents, direct catheterization, etc). Having studied this huge and unique material we have defined biologically important peculiarities of the functioning of this blood circuit during a uterine contraction. It is a well-known fact that as the intraamniotic bloodflow increases the intensity of uteroplacental bloodflow progressively decreases. For instance, when the tension in the amniotic cavity is 10 mm Hg., the intensity inbetween contractions is at the average 350ml/min, and under the intensity of 50 mm Hg, it makes up a total of ≈ 17,5 ml/min. (5 % of the initial). Thus, the dicreasing dynamics of the bloodflow intensity in a circuit is the following: under the tension in the amniotic cavity of 20 mm Hg. ≈ 262,5 ml/min, under 30 mm Hg ≈ 175 ml/min, under 40 mm Hg. ≈ 87,5 ml/min. It is high time we reminded of the stated fact that after the intramyometric (intraamniotic) tension has reached 27-30 mm Hg. the blood outflow from intervillous space is blocked, while it goes on receiving blood.When a physiological uterine contraction is effective, the period of time with the tension in amniotic cavity of 27-30 mm Hg. is 30-45 sec.This period of time has the same duration as birth pangs and duration of a contraction. In real, a contraction lasts much longer. During the 30-45 seconds the veils of the uteroplacental circuit and intervillous space deposit 45-75 ml of blood under tension that inevitably results in increase of volume of the vascular bed of circuit.

Cervical circuit. This blood circuit of uterus during labor is quite “unlucky”. While the leading obstetricians of the past were very much aware that to the moment of delivery the cervix turns into a cavernous body, though did not understand the physiological meaning of its lacunal transformation, modern authors of text books and guides do not even mention this phenomenon indicating the matuaration of cervix for delivery. Our attempts to link this phenomenon to biomechanics of uterine contraction as well as thorugh articles by
S. Voskresnsky have encouraged most inquisitive obstetricians and morphologists to slowly but steady search for the answers to the questions. Today it is a well-known fact that right before the delivery the bloodflow in the cervical circuit reinforces. This is one of the most important indications of uterus maturation for delivery. We should understand that cervical circuit is drained only through the lower uterus drain circuit with its tension rising during contractions. The reinforcing occlusion of the lower segment tissue and cervix as it dilatates during uterine contraction also blocks the venous outflow from the cavernously transformed venous network of its tissue. Part of lacunas receive arterial blood directly from arterio-venous shunts, the rest receive blood that is transported under tension from the veins of the diving venous sinus and lacunary transformed veins of the inner muscular layer of uterus. The brighter is the cavenous-like transformation of cervix, the larger amount of blood can be deposited into the lacunas of its venous bed thus changing the volume of its tissue. There is no doubt that a phenomenon of forced blood depositing into uterine lacunas during uterine contraction. Only it is still unclear, how the own arterial-arteriolar system of cervix “contributes” to the volume of the blood deposited under tension, and what amount of blood under tension is transported from the upper sections of uterus. It is an objectively real fact that the peculiarities of a uterine act course are directly linked to both - the amount of lacunary transformed vessels and that of blood deposited during uterine contraction.

Дата добавления: 2015-10-30