Kinematics of the fetus through the birth canal (biomechanism of labor)

The movement of the fetus through the birth canal is a section of Biophysics of delivery, considering the specified process. The main driving force providing the fetus, are the contraction of the uterine muscles.
The movement of the fetus through the birth canal is extremely straightforward and much more complex - translational-rotational. It is due to the sum of static and dynamic factors, depending on the anatomical and functional characteristics of organisms mother and fetus. Among them are: the structure of the (curved) and the size of the birth canal, the value of the fetus (in particular the size of the head, the weight of the ovum in General (gravity), the effectiveness of contractile activity of smooth muscles of the uterus, striated muscles lining the small pelvis (the so-called wall), and muscles of the anterior abdominal wall, peculiarities of the structure and functions of the ligaments of the uterus and pelvic etc.
The fruit is surrounded by a liquid that is a kind of shock that reduces force of pushes, movement of the foetus under the influence of endogenous and exogenous irritants, and when the impact on the mother's body.
Thanks to the shock-absorber at the same time protected the interests of organisms mother and fetus.
In addition, the amniotic fluid balance intrauterine pressure during labour and undertakings, supporting the correct functioning of the placenta, thus preventing the fruit from asphyxia. Finally, the lower pole membranes with dome-shaped form, is a kind of stimulator receptor apparatus of the uterus.
Energy power arising from the uterus is transmitted through the amniotic fluid on the fruit; it is the main casts out (hydrostatic) force.
However, full expulsive force includes in addition to the main hydrostatic forces the additional force, which is calculated for the account of one of the components of the gravity of the ovum generally, average weight of which is 4.5 kg (fruit - 3 kg, the last 500 g and amniotic fluid - 1 kg). Decomposing the force of gravity by the rule of the parallelogram of forces into two parts - one parallel axial movement, and the other perpendicular to it, we can determine that a parallel power, contributing to the promotion of fruit, on average, equal to 2 kg, and perpendicular to, the holding fruit to the uterine wall (and to the spine), is almost 3.5 kg. Thus, lateral pressure on the uterus, due to the gravity of the fetus, almost equal to its weight.
In the period of exile full expulsive force becomes greater as the work included all of striated muscle system. The latter is necessary in part because the motion of the fetus on curved birth canal requires effort on 10-11% more than during its motion along the straight channel (A. N. Pressman and gg Brilling). It also adds the resistance of the muscles and ligaments of the small pelvis (the pelvic diaphragm and others).
Given all the above, it follows that at physiological during childbirth axial forces in the period of disclosure varies in the range of 6-7 kg, and in the period of exile is increased up to 8-9 kg and above (I. I. Yakovlev and B. A. Petrov and others). According to A. B. Presmana and gg of Brilling, the expulsive force in the first period of confinement average of 11.1 kg, while in the second period - from 12.8 to 13.1 kg
Brief data on the expulsive power of great importance when considering the biomechanism of labor.
When translational movement of the fetus through the birth canal head it performs consistently and gradually five kinds of movements.
The severity of these movements depends on the size, shape and configurability the head of the fruit, on the one hand, the magnitude and characteristics of the shape of the pelvis, its size in separate planes, as well as the status of elasticity of the soft tissue lining the inside of a large and especially the small pelvis.
Separate kinds of movements following: flexion and extension in the horizontal plane, internal rotation around the vertical axis (rotational movement), side decline head (syncleticea) in one direction or another shoulders, pendulum-like or swinging motion of the head of alternate deviation swept seam from the axis of the pelvis in one direction or another - sacral rotation.
Axial movement of the fetus, as playacalida differs from acyclicity that asinkritos usually one-sided affair (front or rear) and relatively stationary.
In close connection with syncletica is the configuration process the head of the fruit, which begins when joining her in the pelvis and is stored in the future.
The configuration process allows the cylinder, to adapt to the movement of the pelvis, and began to be more completely to use all the capacity of the pelvis.
Configuration with front-view occipital presentation is made in such a way that prednamerennoe bone coming on saddlemen and at the same time parietal bone looming on the frontal and occipital. Parietal bone in comparison with the frontal and occipital bones have the greatest mobility and flexibility.
Pendulum-like, or swinging, movements of the head of the fruit in the basin depend on the mobility of its relation to the body (more precisely, shoulder zone); their relationship is based on the principle of action ball bearings rate driven by, as noted earlier, the shape and size of the pelvis, as well as resistance from the cervix (up to full disclosure).
Such is the nature of the movements of the fetus was described in 1930 in the manual for doctors prepared by me together with P. A. Beloshapko, and denoted by the term "sacral rotation". So, naturally, is surprising article Besolds Fr., opening this long-outdoor" phenomenon, which in its time was still mentioned in lectures centuries Transfiguration, developing a teaching C. D. mikhnova.
On a table. 27 the peculiarities of biomechanism of labor in different types of presentation.

The passing of the head of the fetus through the birth canal