## 2 Materials and Methods
### ONIRY Meter and ONIRY Probe  
The ONIRY Meter is an impedance spectroscopy device. It allows for measuring bioimpedance of the tissues through the ONIRY Probe. The main parameters measured were impedance module and impedance phase shift. The impedance was established based on [PERSON]'s law. The module can be calculated as the square root of the sum of resistance and capacitance, both squared. The phase shift can be estimated by finding the arc tangent of the ratio between capacitive and resistive components. All are calculated by the device. A block diagram of the version used in the study is shown in Figure 1.  
The selection of application and measuring electrodes is made using a set of multiplexers. The application electrodes apply current (generated by a bidirectional current source) with an amplitude of less than 1 mA to the patient's body, while measuring electrodes record the voltage change. The measured signal is amplified and adjusted to meet the specification of the impedance converter. The whole process is controlled by the STM32 microcontroller, which is also responsible for saving the test data to the microSD card. In this study, measurements from each probe position were saved in a separate file. After switching on the device, calibration should be performed by connecting three plugins with test impedance values to the cable connector, parallel connection of resistor, \(Rp\), and resistor \(Rs\) in series with capacitor \(Cs\):  
* \(Rp=510\ \Omega,Rs=100\ \Omega,Cs=10\ \mathrm{nF}\),
* \(Rp=82\ \Omega,Rs=100\ \Omega,Cs=32\ \mathrm{nF}\), and
* \(Rp=500\ \Omega,Rs=2.2\ k\Omega,Cs=2\ \mathrm{nF}\). If necessary, it is also possible to calibrate the device during its operation. After a positive calibration result, the investigator connects the probe and can start the measurement by pressing the button on the front panel of the housing. After the measurements, the investigator removes the microSD card from the device and all files from the examination can be uploaded to anelectronic Case Report Form (e-CRF, provided by the CRO of the trial; later versions will have a more automatic process for data transfer). The ONIRY Meter is a battery-powered device, therefore there is no direct risk of electric shock to the patient. The ONIRY Probe is an elongated, rounded probe, which, when inserted into the body cavity (anal canal), is able to precisely measure the bioimpedance of adjacent tissue \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Visit Number** & **0** & **1** & **2** \\ \hline Written consent to participate in the study (patient’s informed consent form) & X & & \\ Assessment of inclusion/exclusion criteria & X & X & \\ Assessment of vital signs & X & X & X \\ Neonatal and gynecological interview \& medical history & X & \\ Physical examination & X & X & X \\ Evaluation of fecal incontinence symptoms using the Wexner scale & & X \\ Gynecological examination & & X & \\ Proctological examination & & X & \\ Collection of blood and stool samples & X & \\ pH measurement of the vagina & & X & \\ Impedance spectrometry testing using the ONIRY device & & X & \\ Endoanal ultrasound & & & X \\ Anorectal manometry & & X & X \\ Monitoring of adverse events & & X & X \\ Determining the degree of sphincter injury and planning the treatment & & X \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Schedule of visits during the study. that may allow for concluding the presence and location of an injury. It is based on the tetrapolar measurement strategy using 4 silver electrodes, where two of them (outside) are used as application electrodes and the other two (inside) as measuring ones.