The blood supply to the uterus comes from two sources: from the uterine artery (a. uterina), originating from the internal iliac artery (a. iliaca interna), and the ovarian artery (a. ovarica). The uterine artery runs at the base of the broad ligament, reaches the lateral wall of the uterus and, at the level of the internal os of the cervix, turns upward, giving off the vaginal artery (a. vaginalis), which runs along the anterolateral wall of the vagina, nourishes its upper third and connects with the same branches of the opposite side . The upper part of the uterine artery is often divided into two, sometimes into three branches, one of which goes to the fundus of the uterus, the other to the mesentery of the ovary.

The arterial vessels of the myometrium exhibit independent contractile activity, regardless of the contractile activity of the uterus, especially in the subplacental zone. Spontaneous contractions of the arteries of the human uterus outside pregnancy are characterized by two vascular rhythms. The first type of rhythmic contractions is 2-3 contractions in 10 minutes (characteristic of the first phase of the menstrual cycle with high estrogen saturation). The second type is in the second phase of the menstrual cycle, when there is a significant increase in the amplitude of contractions; The basic rhythm of contractions of the vascular wall is superimposed on rapid contractions of the arteries with very low amplitude and high frequency.

Spontaneous contractile activity of the arteries, which causes instantaneous changes in the lumen of the vessels, is a decisive factor in maintaining a continuous and optimal blood supply to the uterus.

Ovaries and the fallopian tubes they receive blood from the ovarian artery, which arises from the abdominal aorta and descends into the pelvis along with the ureter. Having reached the ligament that suspends the ovary, the ovarian artery approaches the hilum of the ovary and gives off some of its branches. The other part anastomoses with the uterine artery.

The arteries are accompanied by veins of the same name, which in the parametrium form powerful venous plexuses that anastomose with each other (vesical, uterine, rectal, ovarian). There are multiple venous collectors in the myometrium.

The veins of the uterus do not have valves that prevent the blood from flowing back. The venous system, which receives a large amount of blood (up to 1 l), is a kind of hydrodynamic system that regulates the outflow from the myometrial and placental circulation circuits.

During labor, part of the venous blood is deposited in the venous collectors of the uterus, thereby providing almost constant pressure in the intravillous spaces.

During pregnancy, along with an increase in the mass of the myometrium, additional arterial and venous vessels form in the wall of the uterus, resulting in the uterus being a tangle of vessels. A healthy young woman maintains a stable number of vessels in the uterus. However, the vessels of the uterus change greatly during gestation. During pregnancy, the number, length, and tortuosity of arterial and venous vessels increase many times over. Numerous arteriovenous and arterio-arterial anastomoses are formed. Between the layers of the myometrium, especially between the inner and middle layers, numerous venous cavities (settlements, collectors) are formed, necessary for the deposition of venous blood. The walls of the venous cavities are structurally connected with muscle bundles that separate and unite the individual muscle layers of the myometrium. Venous cavities form the basis of the dividing layers and are called the dividing venous sinus.

The spiral arteries pass through the myometrium and basal lamina and reach the intervillous space, where they completely lose their muscle and elastic fibers.

During pregnancy, the main spiral arteries expel the blood they contain due to characteristic contractions directed towards the center of the intervillous space, from where the blood diverges towards the subvillous plate. Having passed through the narrow intervillous space, the blood returns through the venous canals of the placental septa and reaches the spongy layer of the uterus. Up to 1/3 of the venous blood passes through the drainage in the marginal sinus every minute.

In the intervillous space of the maternal part of the placenta, the arterial circulation is combined with the venous one.

In the fetal part of the placenta there is also a network of capillary vessels between the arteries and veins of the umbilical cord. These structures form, in the intervillous space, “pads” of capillary vessels of the fetus, which facilitates placental exchange.

The volume of the vascular bed and blood flow of the uterus during pregnancy increase many times. With the onset of pregnancy, vascular resistance decreases by 30-40%.

During pregnancy, in terms of blood supply, the uterus is equated to vital organs (heart, brain); outside of pregnancy, the uterus is supplied with blood as peripheral organs.

Spontaneous contractions of the myometrium and the vessels themselves regulate the flow of arterial and outflow of venous blood. The diameter of the vessels is of great importance. A narrowing of their lumen by 50% leads to a 16-fold increase in vascular resistance, so diseases and complications of pregnancy associated with vasospasm (hypertension, late gestosis, the presence of myomatous nodes in the thickness of the myometrium, as well as increased basal tone of the uterus) can cause prolonged ischemia of the uterus, increased contractile function and the development of placental insufficiency (premature termination of pregnancy).

Blood flow in the uterus depends on the content of hormones in the blood (estrogens, progesterone), as well as mediators of the sympathetic and parasympathetic systems.

The vessels of the uterus are innervated by a large number of sympathetic nerves. Postganglionic nerves arising from the pelvic and para-aortic plexuses form a perivasal network that runs along the blood vessels. Parasympathetic fibers have a similar course.

Currently, a close interdependence of the basal tone and contractile activity of the uterus with the intensity of blood supply and blood flow in the myometrium has been established.

Initially, the blood supply may change, and then the motor function of the uterus is disrupted, which occurs in pregnant women and women in labor with myomatous nodes [Sidorova I. S., 1979, 1985, 1999, 2003]. At the same time, prolonged uterine hypertonicity is accompanied by a decrease in blood flow in the myometrium against the background of unchanged central hemodynamics.

During pregnancy, spontaneous contractile activity of the uterus is irregular. In the first half of pregnancy, these are contractions of low amplitude and high frequency. They play an important role in ensuring normal blood supply to the myometrium.

In the second half of pregnancy, spontaneous uterine contractions are characterized by higher amplitude and low frequency, which in the last month of pregnancy turn into prenatal contractions. Myometrial contractions regulate the flow of blood to various parts of the uterus, promoting sufficient perfusion of the myometrium.

The blood flow fully provides the trophic needs of the myometrium and adequate supply to the fetus, but the blood supply is different, therefore the myometrial and uteroplacental blood flow are distinguished. The intercellular substance in the myometrium connects with its capillary system, and therefore the reaction of the vascular bed significantly affects the metabolism of myometrial cells. A decrease in myometrial blood flow leads to insufficient supply of the uterus with oxygen, glucose, biologically active compounds and hormones.

Impaired hemodynamics as a result of uterine hypertonicity can lead to disruption of the metabolism of smooth muscle cells and “biochemical trauma of the myometrium,” which is expressed in a decrease in the firmness and elasticity of muscle tissue. This can cause a rupture of the uterine wall during a difficult birth (the so-called Verbovsky uterine rupture).

The state of blood vessels and blood circulation in the uterus are decisive factors in maintaining metabolic processes in the myometrium at an optimal level.

There are two groups of factors influencing the vascular bed of the myometrium. The first group is factors that reduce blood flow: these are mediators of the sympathetic nervous system(catecholamines), vasoconstrictors, increased basal tone of the uterus. The second is factors that increase blood flow: mediators of the parasympathetic nervous system (acetylcholine), β-blockers, β-adrenergic agonists, as well as β-adrenergic receptor stimulants (partusisten, ginipral), antispasmodics (no-shpa), estrogens, inhibitors of prostaglandin synthesis (indomethacin) , GABA (phenibut), etc.

The vessels of the uterus, like myometrial cells, have two types of adrenergic reception. Drugs that excite adrenergic receptors cause vascular contraction, while drugs that stimulate β-adrenergic receptors lead to their relaxation.

Under normal conditions, the sympathetic and parasympathetic subsystems are in a state of dynamic equilibrium, which ensures normal contractile activity of the uterus both during pregnancy and non-pregnancy, as well as its optimal blood supply.

Violation of this balance leads either to the functional dominance of the sympathetic system, which causes uterine ischemia (increased uterine tone, hyperexcitability), or to the predominance of the tone of the parasympathetic nervous system, in which dilation of the blood vessels of the uterus and venous stagnation are observed. Both disrupt the biochemical processes and energy of uterine contractions.

Hemodynamics in the uterus is a complex process and is closely related to its contractile function.

The myometrial circuit includes arteries, arterioles, capillaries, venules, veins and venous depot, venous collectors (venous sinuses). Before birth, the myometrial circuit contains 800-1000 ml of blood, of which 80-85% flows through the uteroplacental circuit and only 15-20% remains in the uterus.

The uteroplacental circuit includes from 100 to 200 spiral arteries that flow into the intravillous spaces. Their total capacity is 400-500 ml. The spaces are drained by short venous trunks, which flow into the venous depots of the uterus. It must be emphasized that the drainage system in both vascular circuits is the same - this is the venous sinus of the uterus, which unites both circuits into a single hydrodynamic system.

Although both circuits, the myometrial and uteroplacental, function independently of each other, they are closely related to the contractile activity of the uterus. During contractions, endoamniotic and intramyometrial pressure increases, as a result of which myometrial blood flow increases and placental blood flow decreases. By the end of the fight, all indicators characterizing blood flow in both vascular circuits are completely restored. The period of uterine relaxation takes place against the background of hemodynamics restored to the original level.

The increase in blood supply to the myometrium during the pause between contractions is due to the inclusion of deposited blood from the vascular reservoirs of the uterus (250-300 ml of blood), necessary for biochemical reactions.

The coordinated nature of labor is supported by compensatory and adaptive mechanisms that allow maintaining uteroplacental blood flow at the required level.

According to modern concepts, intrauterine pressure and basal myometrial tone are the main regulators of blood flow in the vessels of the uterus, intravillous space and in the placenta. If contractions are too long and strong, or the basal tone of the uterus is excessively high, blood flow through the placenta decreases significantly (up to complete cessation), which can cause intrapartum fetal death.

It has been established that the critical pressure in the amnion cavity, at which blood flow in the intravillous space completely stops and fetal asphyxia occurs, is a pressure above 30 mm Hg. Art. (35-50 mmHg). In this case, the vessels are compressed by the contracted myometrium, the blood volume decreases until it stops.

Intramyometric pressure over 30 mm Hg. Art. possible with severe incoordination of labor, as well as with prolonged pushing.

In most cases, during physiological labor, oxygen and metabolic reserves are sufficient, and due to this, no significant disturbances in the fetal circulation occur. A decrease in uterine blood flow by 20% from the initial level cannot but affect the condition of the fetus, and a decrease of 25% causes fetal hypoxia.

Frequent (more than 5 in 10 minutes) and prolonged contractions, especially against the background of increased basal tone of the uterus, already after 20-30 minutes lead to disruption of the uteroplacental circulation and a decrease in the fetal heartbeat. If the contractile activity of the uterus is not normalized, there is a danger of progression of asphyxia or hemorrhage in the brain.

Important has the degree of oxygen passage through the placental barrier. The amount of oxygen depends on the volume of blood flowing, the hemoglobin content and the partial oxygen tension of the blood.

During discoordinated contractions (long, frequent against the background of high basal tone of the uterus), too little blood (less than 300 ml) enters the intervillous space, resulting in increased pressure in the venous system of the uterus (the risk of premature placental abruption during childbirth).

Under normal conditions, the placenta is pressed, as it were, by the pressure of the amniotic fluid and a certain intrauterine pressure. If the pressure in the venous system exceeds the permissible pressure of the intervillous space, premature placental abruption may occur. This complication often accompanies discoordinated labor.

Oxygen consumption by a full-term fetus weighing 3500 g is 15 ml/min. Under normal conditions, there is a certain margin of safety between the fetal need for oxygen and its supply. The hemoglobin content in the blood and the degree of oxygen saturation play an important role in normal oxygenation of the fetus. A decrease in hemoglobin level to 50 g/l and a decrease in blood oxygen saturation to 30% are critical (the fetus dies).

Common causes of impaired oxygenation of the fetus are uterine ischemia, circulatory failure, low cardiac output in the mother, impaired uteroplacental circulation, and a decrease in the functioning surface of the placenta.

Blood flow in the uterus decreases with high basal tone, with excessively frequent and prolonged contractions and pushing. It depends entirely on the amplitude, frequency and duration of uterine contractions.

With excessive stimulation of the adrenergic receptor system of the myometrium, prolonged spasm of the uterine and peripheral vessels develops, vascular resistance increases, and uterine blood flow decreases.

A similar situation is often observed in the second stage of labor, so prolonged pushing not only has an adverse effect on the fetus, but is also a risk factor for the development of hypotonic uterine bleeding.

The blood pressure in the intervillous space during uterine relaxation is equal to the difference in the pressure of arterial and venous blood at rest. In the intervals between contractions it averages 10 mmHg. Art., which corresponds to the average endoamniotic pressure.

During the peak of a contraction, the flow of arterial blood into the intervillous space and the outflow of venous blood decreases, but during the pause between contractions it quickly recovers. Endoamniotic and intramyometrial pressure during contraction also increases, but the pressure difference in the intravillous spaces remains constant.

During labor coordinated contractions, the oxygen and metabolic reserves of blood located in the intravillous spaces support the vital activity of the fetus for at least 3 minutes with complete cessation of blood circulation. In the case of chronic placental insufficiency, the fetal energy reserves are significantly reduced and this reserve time is absent.

An increase in endoamniotic and myometrial pressure during a prolonged contraction is accompanied by a decrease in blood supply to the uterus and a decrease in blood flow to the fetus, which is reflected in the fetal heart rate (decrease).

Thus, the choroid plexuses of the uterus are functionally related to its contraction and relaxation (systole - diastole of contractions). Mechanical vibrations of the myometrium are transmitted to the walls of blood vessels, causing the mass of blood to move to the lower segment and cervix, then back. This increases the pressure on the internal os and cervix. Peristaltic waves of blood propagate in the middle layer of the myometrium, and it is not possible to detect (feel) them with the hand. The role of a discrete wave of blood in opening the cervix during labor is recognized by many researchers.

Intrauterine pressure (tensio intrauterina)

pressure in the uterine cavity during pregnancy, due to the changing tone of the uterus and the presence of amniotic fluid.

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what “Intrauterine pressure” is in other dictionaries:

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This page is a glossary. # A... Wikipedia

Childbirth ( partus) - the process of expulsion of the fetus from the uterus after the fetus reaches viability.

In the Russian Federation, since 2005, childbirth is considered the birth of a child weighing 1000 g or more at 28 weeks of pregnancy or more. According to WHO recommendations, childbirth is considered to be the birth of a fetus starting from 22 weeks of pregnancy (weight 500 g or more). In our country, termination of pregnancy between 22 and 28 weeks is considered an abortion. Those born alive at this gestational age are given all necessary medical and resuscitation measures. If the child survives the perinatal period (168 hours), then a medical birth certificate is issued and the newborn is registered in the registry office, and the mother receives a certificate of incapacity for pregnancy and childbirth.

In addition to spontaneous labor, there are induced and programmed labor. Induced labor includes artificial induction of labor according to maternal or fetal indications.

Programmed labor is artificial induction of labor at a time convenient for the doctor.

Causes of labor

The reasons for the onset of labor have not yet been established. Childbirth is a complex multi-link process that arises and ends as a result of the interaction of the nervous, humoral and fetoplacental systems, which affect the contraction of the muscles of the uterus. Contractions of the muscles of the uterus do not differ from the contraction of smooth muscle muscles in other organs and are regulated by the nervous and humoral systems.

By the end of pregnancy, as a result of fetal maturity and genetically determined processes against this background, both in the mother’s body and in the feto-placental complex, relationships are formed aimed at strengthening the mechanisms that activate contraction of the uterine muscles.

The activating mechanisms include, first of all, the strengthening of nerve stimuli arising in the ganglia of the peripheral nervous system, the connection of which with the central nervous system is carried out through the sympathetic and parasympathetic nerves. Adrenergic receptors a and b are located in the body of the uterus, and m-cholinergic receptors are located in the circular fibers of the uterus and lower segment, where serotonin and histamine receptors are simultaneously located. The excitability of the peripheral parts of the nervous system and subsequently the subcortical structures (amygdala-shaped nuclei of the limbic hypothalamus, pituitary gland, pineal gland) increases against the background of inhibition in the cerebral cortex (in the temporal lobes of the cerebral hemispheres). Such relationships contribute to the automatic reflex contraction of the uterus.

The second version of the mechanisms that activate uterine contractions, closely related to the first, is humoral. Before childbirth, the content of compounds in the blood of a pregnant woman increases, leading to an increase in the activity of myocytes: estriol, melatonin, prostaglandins, oxytocin, serotonin, norepinephrine, acetylcholine.

The main hormone responsible for preparing the uterus for childbirth is estriol. A special role in increasing its level is played by cortisol and melatonin, synthesized in the fetal body. Cortisol serves as a precursor and stimulator of estriol synthesis in the placenta. Estrogens help prepare the uterus and the mother’s body as a whole for labor. In this case, the following processes occur in the myometrium:

Increased blood flow, synthesis of actin and myosin, energy compounds (ATP, glycogen);

Intensification of redox processes;

Increasing the permeability of cell membranes for potassium, sodium, especially calcium ions, which leads to a decrease in membrane potential and, consequently, acceleration of the conduction of nerve impulses;

Suppression of oxytocinase activity and preservation of endogenous oxytocin, which reduces cholinesterase activity, which promotes the accumulation of free acetylcholine;

Increased activity of phospholipases and the rate of the “arachidonic cascade” with increased synthesis of PGE in the amniotic membrane and PGF2a in the decidua.

Estrogens increase the energy potential of the uterus, preparing it for long-term contractions. At the same time, estrogens, causing structural changes in the cervix, promote its maturation.

Before birth, the uterus becomes estrogen-dominant with a predominant activity of a-adrenergic receptors and a decrease in b-adrenergic receptors.

An important place in the initiation of labor belongs to melatonin, the concentration of which increases in the fetus and decreases in the mother. A decrease in the level of melatonin in the mother's blood promotes the expression of folate and lutropin, leading to the activation of estrogen synthesis. Melatonin not only increases estrogen function, but also activates immune responses by suppressing the synthesis of the immunosuppressants prolactin and choriogonadotropin. This, in turn, enhances transplant immunity and stimulates rejection of the fetus as an allograft.

For the onset of labor and contraction of the muscles of the uterus are important PGE and PGF 2a - direct activators of labor. The first of them greatly contributes to cervical ripening and uterine contraction in the latent phase, and PGF2a - in the latent and active phase of the first stage of labor.

An increase in the synthesis of prostaglandins is due to the activation before birth of the “arachidonic cascade” as a result of dystrophic changes in the decidua, fetal membranes, placenta, as well as the release of fetal cortisol and an increase in estriol.

Prostaglandins are responsible for:

Formation of a-adrenergic receptors and receptors for oxytocin, acetylcholine, serotonin on the muscle membrane;

Increased levels of oxytocin in the blood due to inhibition of oxytocinase production;

Stimulation of the production of catecholamines (adrenaline and norepinephrine);

Ensuring automatic contraction of the uterine muscles;

Deposition of calcium in the sarcoplasmic reticulum, which contributes to prolonged contraction of the uterus during childbirth.

One of the important regulators of the contractile activity of the uterus is oxytocin, secreted in the hypothalamus and released before birth by the pituitary glands of both the mother and the fetus.

The sensitivity of the uterus to oxytocin increases in the last weeks of pregnancy and reaches a maximum in the active phase of the first period, in the second and third stages of labor. By increasing uterine tone, oxytocin stimulates the frequency and amplitude of contractions by:

Excitation of a-adrenergic receptors;

Reducing the resting potential of the cell membrane and thereby the threshold of irritability, which increases the excitability of the muscle cell;

Synergistic effect on acetylcholine, which increases the rate of its binding by myometrial receptors and release from the bound state;

Inhibition of cholinesterase activity, and, consequently, the accumulation of acetylcholine.

Along with the main uterotonic compounds in the process of preparation for childbirth important role belongs serotonin, which also inhibits the activity of cholinesterase and enhances the effect of acetylcholine, promoting the transmission of excitation from the motor nerve to the muscle fiber.

The change in the ratio of hormones and biologically active substances that affect the excitability and contractile activity of the uterus before childbirth takes place in several stages: the first stage is the maturity of hormonal regulation of the fetus (cortisol, melatonin); the second stage is the expression of estrogens and metabolic changes in the uterus; third stage -

synthesis of uterotonic compounds, primarily prostaglandins, oxytocin, serotonin, ensuring the development of labor. The processes occurring before childbirth in the central and peripheral nervous system, endocrine system and fetoplacental complex are combined into the concept of “generic dominant”.

During childbirth, alternating excitation of the centers of sympathetic and parasympathetic innervation develops. Due to the stimulation of the sympathetic nervous system (norepinephrine and adrenaline) and the release of mediators, the longitudinally located muscle bundles in the body of the uterus contract while the circularly (transversely) located bundles in the lower segment are actively relaxed. In response to maximum excitation of the center of the sympathetic nervous system and the release of a large amount of norepinephrine, the center of the parasympathetic nervous system is excited, under the influence of mediators of which (acetylcholine) the circular muscles contract while the longitudinal ones relax; after achieving maximum contraction of the circular muscles, maximum relaxation of the longitudinal muscles occurs. After each contraction of the uterus, its complete relaxation occurs (pause between contractions), when the synthesis of myometrial contractile proteins is restored.

Table of contents of the topic "Registration of contractile activity of the uterus. Hysterography. Cardiotocography (CTG).":
1. Registration of contractile activity of the uterus. External hysterography. Multichannel external hysterography. Hasina formula.
2. Internal hysterography (tocography). Registration (measurement) of intrauterine pressure. Units of Montevideo.
3. Radiotelemetry. Cardiotocographs.
4. Intrapartum cardiotocography. Indications for intrapartum cardiotocography (CTG).
5. Evaluation of cardiotocography (CTG) data. Basal rhythm. Normal basal rhythm. Basal rate. Fetal heart rate variability.
6. Oscillations. Normal oscillation amplitude. Undulating curve type. Variability of oscillations.
7. Accelerations. Sporadic, periodic accelerations. Decelerations. Sporadic, periodic decelerations.
8. Classification of decelerations. Early, late and variable decelerations.
9. Atypical variable decelerations. Amplitude of decelerations. Assessment of uterine activity.
10. Interpretation of cardiotocography (CTG). Clinical evaluation of cardiotocography (CTG) data. Saltatory rhythm of fetal heart contractions.
11. Sinusoidal rhythm of fetal heart contractions. Krebs scale. Krebs score. Krebs points. Zaling's test.
12. Algorithm for managing labor in case of fetal cardiac dysfunction.

Internal hysterography (tocography). Registration (measurement) of intrauterine pressure. Units of Montevideo.

With internal tocography(the sensor is located in the uterine cavity) register intrauterine pressure outside and during contractions, which indirectly, but quite accurately allows one to judge the characteristics of the contractile activity of the uterus.

The first intrauterine tocography applied in 1871 by F. Schatz, who inserted a gutta-percha balloon with a diameter of 3 cm into the uterine cavity and made a recording. Subsequently, many studies aimed at improving internal hysterography appeared.

For registration of intrauterine pressure The most widespread method is the iptraamnial insertion of an open catheter through the cervical canal. Less commonly, balloons of various diameters were introduced into the uterine cavity for tocography. Extra-amnial placement of an open catheter and balloons is currently practically not used due to the insufficient accuracy and danger of the method.

Rice. 6. Multichannel internal hysterography (scheme).

The fundamental research of R. Caldeyro-Barciaefal deserves special attention. (1960), who, to study the contractile activity of the uterus, transabdominally introduced an open catheter into the uterine cavity and microballoons with a capacity of 0.02 ml into the myometrium of various parts of the uterus (fundus, body, lower segment). This allowed the authors to study in detail the appearance and propagation of the contraction wave, the tone of the uterus, the amplitude and duration of contractions, the interval between contractions, etc. They were able to scientifically confirm the concepts " triple downward gradient" And " dominant of the uterine fundus" (Fig. 6), identify various forms of discoordination of labor, propose a method for assessing uterine activity in Montevideo units.

Due to the danger and non-physiological this registration method is not widespread in practical obstetrics, although its scientific value is enormous.

All modern foreign cardiotocographs In addition to the external sensor, they have devices for recording intrauterine pressure.

Intrauterine (amniotic) pressure is the result of contractile activity of various parts of the uterus; Registration of its value will make it possible to judge the activity of the organ as a whole. The presence of good coordination between different parts of the uterus is proven by the fact that during uterine contractions the amniotic pressure recording curve has a regular sinusoidal shape. Synchronous relaxation of all parts of the uterus during normal labor leads to a gradual decrease in amniotic pressure to the level of normal tone outside of contractions.

At discoordination of labor hysterographic curve takes on an irregular shape as the pressure increases or decreases, or throughout all contractions. When labor is weak, contractions are rare, of low intensity and duration,

Internal tocography methods compare favorably with external hysterography methods, since with their help it is possible to obtain reliable data during and outside of contractions in certain units of measurement (mm Hg), as well as a more accurate description of the duration of contractions over time. However, these methods have some disadvantages (forced positioning of the woman in labor, the risk of infection and premature opening of the membranes).

Some authors consider the uterus to be a pronounced organ of movement, which is manifested both in its continuous contraction (tone) and in periodic contractions (contractions) observed in pregnant women, women in labor and postpartum women. The completion of the physiological role of the uterus as a receptacle for the fetus and an organ of movement is the process of childbirth - the development of fetal expulsion forces.

The process of childbirth differs from the actual contractions of the uterus in the non-pregnant state and during pregnancy. The expelling forces are a complex of contractions of the uterus (contractions) and abdominal contractions (pushing) that join them in the second stage of labor. Contractions of the vaginal muscles also play a role.

Contractions are regular, periodically repeated contractions of the smooth muscles of the uterine body (hollow muscle), which do not obey the will of the woman. A woman in labor can only strengthen or weaken her efforts to a certain extent. Attempts are observed during the second and third periods of labor.

According to Ya. F. Verbov, Bumm et al., labor contractions are peristaltic in nature towards the exit of the birth canal. However, peristalsis in the human uterus is difficult to observe, since the wave of contraction spreads too quickly throughout the organ.

According to Ya. F. Verbov (1912), the muscle fibers in the uterus are located mutually perpendicular; they are antagonistic and cannot contract simultaneously. The onset of labor is characterized by the fact that the fundus of the uterus gradually begins to descend and by the end of the period of dilatation it stands 3-4 fingers below the urinary process. The uterus shortens due to the opening of the cervix and at the same time noticeably increases in width and in the anteroposterior direction. All this occurs under the influence of contraction of the longitudinal fibers of the uterus in the first stage of labor. At the very end of the opening period, contractions are more sensitive precisely because at this time the contractions of the longitudinal muscles are highly energetic.

Figure: The size and shape of the uterus at the beginning (a) and at the end (b) of the dilatation period (Ya. F. Verbov).

After opening of the amniotic sac, the shape of the uterus changes dramatically, becoming narrow and long, and the fundus of the uterus rises. At the beginning of the second period, the fundus of the uterus is one transverse finger below the xiphoid process; when the fetal head penetrates and erupts, the fundus of the uterus goes under the edge of the ribs, its width decreases (20-18 cm). During this period, the circular muscle fibers of the uterus contract.

Figure: The size and shape of the uterus at the beginning of the expulsion period (Ya. F. Verbov).

Figure: Size and shape of the uterus at the end of the expulsion period; the uterus bends anteriorly (Ya. F. Verbov).

In the first stage of labor, the longitudinal muscles have support at the site of attachment of the round ligaments and in the fascia pelvis; The abdominal press is not involved in contractions. In the second period, the uterus arches anteriorly, stretches the fascia of the abdominal wall, as a result of which the muscles of the latter contract strongly. The muscles of the abdominal wall press on the uterus, flatten it, and the uterus, resting its bottom against the overlying organs and the anterior abdominal wall, acquires greater expelling force. In this alternation of the work of longitudinal and circular muscles, Ya. F. Verbov sees the “law of peristaltic movement of the uterus,” since “peristalsis is the movement carried out by the alternating work of longitudinal and transverse muscles.”

Regarding this theory, it must be said that the clinic of childbirth is presented by the author correctly, but the definition of peristalsis and its “law” is incorrect, since peristaltic movement is a rapidly alternating contraction of both longitudinal and transverse muscles, and not a contraction during the periods of labor, as I describe it . F. Verbov.

During the first stage of labor, a phenomenon called retraction occurs in the muscles of the uterus. It consists of the following: with each contraction of a hollow muscle, the arrangement of the muscle fibers mutually changes, and the fibers that lay one after the other before the contraction now lie parallel; Part of the fiber, rising higher, becomes wedged among other fibers. The fibers retain their new position after the contraction. A new contraction leads to a new, even more significant displacement of muscle fibers. Ultimately, as labor intensifies, retraction leads to thickening and shortening of the hollow uterine musculature. Simultaneously with retraction, another process occurs - distraction, that is, stretching of the muscle fibers of the neck. Distraction occurs due to the fact that during retraction, the longitudinal muscle fibers of the hollow muscle pull upward the circular fibers of the neck, which gradually stretch. Due to retraction of the fibers of the hollow muscle and distraction of the neck, the border between the hollow muscle and the lower segment is marked in the form of a muscle cushion or retraction ring.

Figure: Retraction of muscle fibers in the uterine wall during labor.

a – stretched muscle; b – contracted muscle.

A – artery; B – vein.

The next feature of uterine contractions during childbirth is their segmental nature. We can consider that the uterus consists of two functional sections - the body and the cervix. The possible border between them lies at the internal pharynx. The synergistic action of the sympathetic and parasympathetic nervous systems during labor leads to the stimulation of body contractions and simultaneous relaxation of the neck.

The segmental nature of contractions can sometimes be observed in the lateral sections (horns) of the uterus. And, indeed, during childbirth one can sometimes notice that contractions of the uterus are observed only on one side of it, while the other almost does not contract at all. From the point of view of the laws of development, this phenomenon is explained by a return to the type of functions usual for a bicornuate uterus. From a physiological point of view, the higher the uterus is developed, i.e., the more completely the fusion of the Müllerian ducts has occurred, the more coordinated the movements of the entire organ are during labor.

This segmentation of contractions of the uterine muscles, both vertically and horizontally, will be understandable if we take into account that the muscle fibers in the uterus are located perpendicularly or obliquely in relation to each other.

IN Lately The significance of the tone of the uterus and the amplitude of its contractions for the course of labor was determined. During uterine contractions of the hollow muscle, some of the fibers move upward from the isthmus and cervix. Moreover, if the general resting tone of the uterus is low, then before contraction occurs, the walls of the uterus must gradually come into a state of tension. If the resting tone is high, then the slightest contraction of the motor part of the uterus will be reflected in the cervix, the fibers of which, in a state of tension, will come quickly and cause it to open. Thus, the significance of the initial high tone of the uterus is the rapid transfer of the force of contractions of the motor part of the uterus to the pharynx, and the opening of the latter occurs quickly. Another importance of good uterine tone is to maintain the achieved level of cervical dilatation. Thus, we consider moderately high tone to be a favorable phenomenon for rapid dilation of the cervix and rapid progress of labor. On the other hand, excessively high uterine tone can cause significant pain in the absence of contractions and spastic weakness of labor.

There is a complete relationship between the resting tone and the amplitude of contractions: as the resting tone increases, the amplitude of contractions decreases. A small amplitude of contractions does not affect the course of labor if the tone is good.

The following data are available about intrauterine pressure. Intrauterine pressure before birth is 20 mmHg. Art. During childbirth, intrauterine pressure fluctuates: outside contractions it is on average 50 mm, at the height of contractions it is about 80 mm, and during abdominal contraction it is about 95 mm Hg. Art. Distribution of intrauterine pressure during dilatation. The high blood pressure of the blanket (measured during a cesarean section through the umbilical cord), reaching 160-180 mm, explains the relative harmlessness to the fetus of high intrauterine pressure during contractions and pushing. The relationship between intrauterine and blood pressure during childbirth is such that an increase in intrauterine pressure during contractions is accompanied by an increase in maternal blood pressure by 10-20 mm.

Figure: Distribution of intrauterine pressure during dilatation (diagram).

During a contraction, there is a decrease in blood pressure in the vessels of the placenta, and the latter is partially exsanguinated. Uterine ischemia that develops during contractions threatens the fetus with asphyxia, therefore, at the moment of cutting and eruption of the head, when intrauterine pressure is especially high, the danger of fetal asphyxia increases.

An objective study of a woman's uterine contractions, especially during childbirth, presents significant difficulties.

Winkel's method - examination with a hand placed flat on the stomach at the bottom of the uterus, counting the duration of each contraction and pause in the second hand of the clock - is primitive and inaccurate.

The methods used for instrumental study of uterine contractions can be divided into two groups:

1) internal hysterography - the study of uterine contractions using a balloon inserted into its cavity and 2) external hysterography - the study of uterine movements using devices placed on the woman’s abdominal wall.

For internal hysterography, a tocodynamometer apparatus was proposed, which consists of a small rubber balloon connected by a rubber tube to a T-shaped glass tube, to both ends of which two mercury manometers are attached. One of the pressure gauges contains a float ending with a pen for recording the curve of uterine contractions on a kymograph. The balloon is inserted into the uterus from the side of the fetal breast and filled with water; the remaining parts of the apparatus contain air. This device was used to study contractions of the uterus under the influence of quinine, chloral hydrate, ether and pituitrin. Internal hysterography methods are now rarely used due to the risk of infection in the uterus.

Figure: Diagram of the apparatus for internal hysterography.

1 – uterine balloon filled with water; 2 – writing apparatus; 3 – water injection device; 4 – kymograph.

External hysterography, which does not violate asepsis, received widespread. Devices for external hysterography were originally based on the principle of air transmission using a rubber membrane acting on the Murray drum. Uterine contractions were recorded on a kymograph. More advanced are devices without air transmission - hysterographs with direct recording; in them, the pressure of a spring applied to the abdominal wall is transmitted to a writing stylet or pencil, and the recording is made on a long paper tape moving mechanically under the stylet.

Figure: Apparatus for external hysterography.

a – with air transmission; b – with direct recording.

S. A. Yagunov (1936) used external hysterography as follows. A fabric belt was placed on the mother's belly, at the level of the navel, under which a rubber bandage (6X20 cm) was located. The latter is pneumatically connected by a rubber tube to the Murray drum. The curve can be recorded with a Murray drum pen or photographically using a Myasishchev apparatus. In this case, contractions and attempts are transmitted pneumatically to the Murray drum, the vibration of which causes movement of the mirror associated with it. A light beam from the mirror falls on a moving strip of photographic paper, which produces an image of a curve. I. I. Yakovlev used the method of recording its bioelectric currents to study contractions of the uterus. All such devices need improvement.