Role of myometric sysem of uterus in biomechanics of the relaxation phase

It has been established that the musculature of the body of uterus contracts in an isometric mode, without shortening of functional contarcting modules and, consequently, with volume of the cavity of uterus body preserved. It has been also established that any shortening in of the tretched contracting modules of myometrium of uterus body is fixed instantly and irreversibly.

It is an absolutely known fact that as a result of an effective uterine contraction at the period of dilatation part of the fetal-amniotic complex is relocated from the cavity of uterus body into the lower segment cavity and irreversibly fixed by an instant shortening of functional modules. It also results in reducing a part of the fetal-amniotic complex located in the cavity of uterus body, all this happens at the phase of diastole of a uterine contraction. The reason for shortening of functional modules is the primary reducing in the fetal-amniotic complex located in the cavity of uterus body. This process is passive and no linked to the tension of of the relaxing myometrium of the uterus body. Consequently, active relocating of the part of the fetal-amniotic complex from the cavity of uterus body into that of the lower segment is a result of being influenced by other physical processes not directly related to the absolute tension of the muscular shell of this uterus section.

There are more complex and myometrically independent processes taking place in the lower segment of uterus at that time. It is paradoxical, that the rise in volume of the lower segment of uterus takes place at the beginning of labor while the volume of the cavity of the uterus body remains fixed. This continues during every effective uterine cycle untill the lower segment turns into a cylinder. This process is attended by deformation of cervix and relocation of part of the fetal-amniotic complex from the lower segment cavity into the cavity of the deformed cervix, and the plane of the external orifice from the outside. After the lower segment of uterus has been transformed into a cylinder, its volume remains the fixed at any phase of a uterine cycle until the end of the dilatation period. The entire volume of the fetal-amniotic complex being relocated from the uterus body cavity into the lower segment cavity is moved further into the cavity of the deformed cervix.

In order to understand the above-mentioned process of relocation it is necessary to thoroughly examine the chronological characteristics of a definite cycle of cervical deformation during each uterine contraction.

Let us examine a definite cycle of cervical deformation during a definite uterine cycle with physiological course of labor at the beginning of the active phase of dilatation of a primipara. The initial diameter of the external orifice of uterus of a smooth cervix is 5 cm. 6.5 seconds of contraction (rise of amniotic tension) has passed from the beginning of orifice dilatation. The orifice diameter reached its peak (7.5 cm) at the first phase of diastole, with the difference from the peak tension in 8 seconds. It is a starting moment for a reverse deformation of orifice. This process continues the entire diastole time and reaches its peak inbetween the contractions, 18 sec. later after reaching the basal level (5.3 cm) through amniotic tension. Thus, the dimeter of the orifice at its peak of deformation is
2.2 cm wider that the diameter of orifice during the effective uterine contraction. Consequently, the effctiveness of the deformation cycle is 0.3 cm. it turns out to be
7.3 times less than registered at the peak of deformation. An important fact is that the reverse deformation of orifice is carried out under the influence of elastance of cervix tissue and not lineally dependant on amniotic tension. The peak of orifice deformation is linked to changes in cervical geometry and significant rise in volume of its cavity, which is densely filled with the contents of the lower pole of fetal-amniotic complex. It is also important that a significant volume of the fetal-amniotic complex was moved outside the plane of the external pharynx, later it was partly “brought back” during the process of the reverse deformation of cervix. The total volume of fetal-amniotic complex relocated from the lower segment cavity into the cavity of the deformed uterus and outwards the plane of the external orifice is much larger than the fixed at the end of the uterine cycle. As the volume of thecavity of the uterus body and that of the lower segment during systole and at the initial diastole phase is invariable until the the peak of uterus deformation is achieved, and the volume of fetal-amniotic complex during a definite uterine action is a constant – WHAT is the nature of the extraovular intrauterine volume that is involved in active and passive back-and-forth relocation of the lower pole of the fetal-amniotic complex during each of the cervical deformation cycle during physiological uterine contraction? It is an obvious question. The liquid blood that is contained in huge venous depots of myometrium and intervillous space is the only environment hydraulically similar to the liquid contents of the fetal-amniotic complex and located intrauterinary with its volume changing duting uterine contractions.

Дата добавления: 2015-10-30