Continuous controllable balloon dilation: a novel approach for cervix dilation

The study (ISRCTN54007498) was conducted at the Gynecology & Obstetrics Clinics at Kragujevac Clinical Center, Serbia, and Podgorica Clinical Center, Montenegro. The data were collected by the study coordinators at the participating centers. The authors vouch for the completeness and accuracy of the data and analyses. An independent data and safety monitoring board monitored the study and reviewed the protocol compliance and outcome data. The protocol was approved by each participating center's institutional review board.

The patients were enrolled in the study using the following criteria: age between 19 and 40; pregnancy verified by an ultrasound; singleton pregnancy; gestational age ≤10; uterus and cervix with normal findings; and absence of uterine contractions or bleeding.

The study included 120 pregnant women randomly assigned to one of the following three groups: Group I (40 pregnant women), control group with no dilations; Group II (40 pregnant women), dilations performed using Hegar dilators (HeDs); and Group III (40 pregnant women), dilations performed using the CCBD.

The experiments were undertaken with the understanding and appropriate informed consent of each patient.

The CCBD is a fully controllable device for cervical dilation (Figure 1A) based on the use of a specially constructed balloon dilator (BD) that consists of three layers: an inner silicone layer, a central layer made from high-strength fabric, and an outer silicone layer (Figure 1B,C). The maximum BD expansion diameter is limited by the central layer. The outer silicone layer contacts the cervical tissues during dilation. The consistency and endurance of this BD were tested at a pressure of 25 bars, with no detected risk for breakage. The reliability of the CCBD was confirmed in vitro and in vivo (Figure 1D, 1E).

Dilation using the CCBD is performed continuously, with only one dilator placement. In this study, the CCBD was integrated into a system that enables real-time data acquisition and the monitoring of the parameters relevant to the biophysics of dilation (Figure 1A). Dilation dynamics directly depend on the flow of an incompressible fluid into the BD, which is an easily controllable parameter. Because it is an incompressible working fluid, distilled water was used with the addition of nonionic contrast medium (Ultravist-300; Schering AG, Berlin, Germany), which enabled the visual monitoring of dilation using a digital subtraction apparatus for angiography (Figure 1A).

Incompressible fluid from the hydraulic cylinder is pumped to the BD via a flexible hose (hose) and one-way valve (Figure 1A). Fluid flow is controlled by an electric motor that, via a spiral spindles/nut system, provides constant speed of the hydraulic cylinder piston and consequently constant fluid flow. The actual position of the hydraulic cylinder piston and the fluid pressure are monitored by displacement and pressure transducers. The unit for measurement and control collects signals from those two transducers. The pressure gauge is used for visual control of the current fluid pressure, while the pressure reduction valve represents a safety element. After finalization of the dilatation procedure, the choke valve is opened by remote command, which results in draining of fluid from the BD. Then the BD could be easily extracted from the cervical canal. Dilatation duration and maximum pressure in the BD represents parameters assigned by a PC-controlled unit for measurement and control. Those parameters could be monitored in real-time parameters by PC and appropriate acquisition software, which enable full controllability of the cervical canal dilatation process (Figure 1A).

Tissue material for the histological evaluation of cervical damage was obtained from the endocervical mucosa by single curettage (Novac Curette, CooperSurgical, Trumbull, Connecticut, USA) before and after dilation using the HeD or CCBD. The samples were stained with H&E and blinded analysis was performed using a light microscope (Olympus BX 51; Olympus, Hamburg, Germany). The surface areas of the hemorrhagic regions were measured according to a previously published protocol [15].

All of the statistical analyses were conducted using SPSS 13.0 for Windows (IBM, New York, New York, USA). The results were analyzed using Student’s t test. All of the data in this study are expressed as the mean ± standard error. P < 0.05 was considered significant.

The CCBD dilations were successfully performed on all patients. The providers and patients reported no complications or problems with the CCBD, a new dilation technique. The average duration of CCBD dilation was approximately 25.5 seconds (Figure 1F) and was independent of the individual patient's cervical resistance (Figure 1F). The maximal recorded pressure in the BD during dilation was significantly lower than the test pressure for BD consistency and endurance.

The basic biophysical models of cervical canal dilation using the HeD and CCBD are shown in Figure 2. Under the action of an external force F _e (the force required to dilate the cervix at each stage of HeD cervical dilation), the HeD (with diameter D _i ) moves at speed v through the cervical canal (with length L). The external force F _e must overcome the resulting sum of the forces that appear in the direction of the moving HeD. The HeD motion leads to changes in the geometry of the cervical canal. In various ways, the tissue opposes these geometrical changes upon contact with the HeD, which is characterized by the pressure distribution p(x). Because a relatively small zone of the cervical canal is affected by dilation at this time, high contact loads are produced in the tissue (Figure 2A). A detailed overview of the basic forces involved in the contact zones between the HeD and cervical canal tissue during dilation indicates that only one component of the applied external force is responsible for dilation. None of the other forces directly participate in dilation and may lead to a large number of side effects.

In contrast, the CCBD dilation procedure involves inserting the BD in its initial form (diameter D _i  ≈ 4.5 mm) into the cervical canal, which results in a very low resistance to penetration (Figure 2B). Pumping incompressible fluid into the BD increases the outer diameter and pressure of the BD, which dilates the cervical canal. Dilation is performed synchronously along the entire length L of the cervical canal, where the relative movement between the tissue/BD contact pair is reduced to almost zero. In this case, the cervical tissue also opposes changes in its geometry, which is characterized by a much more uniform pressure distribution p(x) (Figure 2B). All of the components of the involved forces participate in dilation, which significantly reduces any side effects.

There was a statistically significant difference in the percentage of epithelial damage (P <0.001), basal membrane damage (P <0,001) and stromal damage (P <0.01) when comparing cervices dilated by the HeD with cervices dilated by the CCBD (Figure 3).

In addition, the extent of cervical hemorrhagia was significantly lower (P <0.01) after CCBD dilation compared with HeD dilation (90% after HeD dilation vs. 32.5% after CCBD dilation; Figure 4).