Methods of recording uterine contractile activity

Diagnostics of labor abnormalities can be performed by analyzing clinical symptoms or using a graphic image of the opening of the uterine os during labor in the form of partograms. Another way to improve diagnostics of labor is to study the contractile activity of the uterus using objective methods: external and internal hysterography. External hysterographs with pneumatic sensors were widely used at one time, however, hysterographs using strain gauges are more advanced, as they are easier to use and inertialess.

The method of internal hysterography is based on the registration of intrauterine pressure (IUP). As early as 1870, the Russian scientist N. F. Tolochinov proposed a manometer mounted in a cylindrical vaginal speculum. The manometer was connected to the fetal bladder and measured the value of intrauterine pressure.

The transcervical method of recording intrauterine pressure using a polyethylene catheter was proposed by Williams and Stallworthy (1982). It has become widespread both in our country and abroad.

One of the options for internal hysterography is the radio telemetry method, the essence of which is that a miniature radio station is inserted into the uterine cavity, which records the intrauterine pressure, converting it into radio waves recorded in the form of curves on a special device.

A device and method for two-channel internal hysterography have been developed. Registration of intrauterine pressure via two channels has become possible due to the discovery of a previously unknown dependence of the uterine self-regulation during labor. During contractions, a zone of increased intrauterine pressure is formed in the lower segment of the uterus due to the emergence of a functional hydrodynamic cavity limited by the lower segment of the uterus, the head and shoulder of the fetus.

Of interest are studies of the contractile activity of the uterus (CAU) using simultaneous recording of intrauterine pressure and external hysterography. Contractions of the uterus begin earlier than the intrauterine pressure increases. At the same time, in the first period of labor, the increase in intrauterine pressure occurs later than the contractions of all parts of the uterus, on average by 9.4 ± 1.5 s.

A comparative analysis of the methods of external and internal hysterography showed that the latter has a number of advantages, since it allows recording the basal (main) tone of the uterus, which is especially important in the diagnosis of hypo- and hyperdynamic types of uterine contractile activity.

The main difficulty in diagnosing uterine contractile dysfunction is to determine the most informative indicators. Several researchers recommend analyzing uterine contractile activity using 15-20 parameters. However, analyzing these indicators requires a lot of time and the use of a computer.

In order to quantitatively evaluate the contractile activity of the uterus based on external and internal hysterography, some researchers have proposed various methods: mathematical analysis of hysterograms, evaluation of the effectiveness of labor based on impulse pressure, i.e. the product of the average pressure value and the time of its action, Montevideo units, Alexandrian units, active planimetric units, etc.

Multichannel external hysterography. Multichannel external hysterography is used for a more detailed study of the contractile activity of the uterus during labor. Five-channel hysterography was used with the location of sensors in the area of the fundus and body of the uterus on the right and left to the lower segment of the uterus along the midline. Later, an electronic hysterograph with a mechanophotoelectronic converter was developed. In recent years, a dynamometerograph has been designed - DU-3 three-channel with ink recording. The device uses modern strain gauge sensors. The device is reliable in operation, portable.

Hysterogram analysis:

• the external hysterogram indicates to a greater extent the dynamics of the volume of the uterus and its membrane at the location of the sensor than the magnitude of the tension of the uterine membrane;
• In the uterus during labor contractions, three hydrodynamic systems can be clearly distinguished:
  • cavity and lining of the body of the uterus;
  • cavity and membrane of the lower segment;
  • the cavity of the vascular depots of the uterus, which influence the amplitude of external and internal hysterograms;
• pathological labor contractions differ from physiological ones not so much in the absolute value of the tension of the myometrium during its contraction, but in the disruption of the order of changes in the volumes of various parts of the uterus, which leads to a disruption of the mechanism for converting the energy of isometric tension of the myometrium into external work to change the tissues of the cervix;
• since external and internal hysterograms have a fundamentally different physical nature, the use of the same methods of their analysis and interpretation is incorrect in relation to the basic physical laws operating in the uterus contracting during labor.

Despite the presence of conflicting data on the contractile activity of the uterus, further study of the qualitative and quantitative characteristics of the contractile activity of the uterus will help to identify such informative indicators of its disorders that can be used for its diagnosis.

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