Perineal electromyography (EMG) is a crucial part of urodynamic studies. Many researchers focused on the standardization of techniques in urodynamics, but no study has yet evaluated the differences with various reference electrode placements. The aim of this study was to determine the optimal placement of the reference electrode for recording pelvic floor activity in urodynamic studies.
Children over 6 years of age without anatomic or neurological abnormalities were invited to participate in the study. Four reference electrodes were placed on the right kneecap, the inner surface of the right inner thigh, the right anterior iliac spine (AIS), and the skin over the left gluteal muscles for simultaneous recording. The EMG signal formed by pelvic contraction during forceful straining was recorded both in the supine and sitting positions. The root mean square (RMS) value of each muscle contraction signal was calculated.
Twenty-one participants (10 boys and 11 girls) were included. The mean age was 10.19±3.20 years. The highest RMS values were obtained with the reference electrode on the thigh in the supine position and the AIS in the sitting position. Significant differences were found between the mean RMS values of the knee and other locations of reference electrodes in the supine position, as well as between mean RMS values in all regions except the thigh and gluteus in the sitting position. The minimum mean RMS values in both positions were obtained with the reference electrode on the knee.
During urodynamic studies, reference electrodes shall be placed on AIS in the sitting and on the inner thigh in the supine position. The knee is not a suitable option for reference electrode placement. This information may help improve EMG recordings in the evaluation of pelvic floor muscles.
Electromyography (EMG) is a diagnostic method to evaluate the muscles and motor neurons [
Perineal EMG is a crucial part of urodynamic studies. A reference electrode is needed when evaluating pelvic floor activity [
Patients over 6 years of age who were scheduled for uroflowmetry in our department with no anatomical or neurological abnormalities were invited to participate in our study. After consent, children were informed about anal sphincter and pelvic floor activity. They were then instructed to tighten their anus in the supine frog-leg position. Patients who had abnormal EMG findings and those who could not perform this maneuver were excluded from the study. This study was approved by the local ethics committee of the Ege University Faculty of Medicine (19- 11.1T/47). The optimization of EMG recordings is particularly essential in pediatric practice; therefore, this study was performed in children. The study was conducted according to the criteria set by the Declaration of Helsinki, and each subject and parent signed informed consent before participating in the study.
Four identical EMG amplifier modules (Aymed Medical Tech, Istanbul, Turkey) with electrically isolated inputs (
A common input was constituted by connecting the negative and positive inputs of each EMG amplifier. Reference electrodes were placed on different locations connected to EMG amplifiers independently. All hardware except the computer was housed in a box with a large metal plate on the base. The negative terminals of the battery and the analog-digital converter were connected to this metal plate to reduce the environmental noise.
All amplifiers and the inputs of the analog-to-digital converter module were made of exactly the same parts or materials, but there may still have been some minor differences. Signals with a known amplitude or potential difference were applied to the inputs of these modules by means of a signal generator in order to overcome this issue. Then, their outputs were measured by means of an oscilloscope and a voltmeter. Calculations were made to assess whether the analog-to-digital converter performed linear digitization. Equations with necessary corrections for existing minor differences were defined in the recording and analysis software.
The signals received from the EMG amplifiers were connected to 4 inputs of the analog-digital converter module, which could run each channel with 16-bit resolution simultaneously and independently. The analog-to-digital conversion module sent the incoming signal to the computer at a rate of 50,000 samples per second. DASYLab software was used as a recording and analysis program. In this software, modules as figures representing certain functions are connected to each other with lines, and then a running program is created. A depiction of the structured program is given in
The root mean square (RMS) is a statistical parameter used to measure the magnitude of varying quantities. It is especially useful in waves where the change is positive and negative. It is defined as the square root of the mean square (the arithmetic mean of the squares of a set of numbers). It represents the magnitude of a waveform in the time axis. The data were analyzed with software prepared with modules in the DASYlab program. The RMS value of each muscle contraction signal was calculated.
After skin preparation with an alcohol-based solution, self-adhesive gel skin electrodes (Aymed, Istanbul, Turkey) were placed on the right and left sides near the anus in the supine frog-leg position. These electrodes were connected to the recording device as active electrodes.
The first electrode to be used as a reference was placed on the skin on the right kneecap, the second on the skin on the inner surface of the right inner thigh, the third on the right anterior iliac spine (AIS) skin, and the fourth on the skin over the left gluteal muscles (
All subjects were taught how to contract the pelvic floor muscles before the recording and were asked to perform one or 2 short-term contraction exercises. During the recording, the subjects were instructed to contract their pelvic floor muscles as strong and long as they could. The EMG signal formed by pelvic contraction was recorded. The recordings were performed twice, in the supine position on the examination table and the sitting position on the urodynamic chair.
The data were analyzed using IBM SPSS Statistics ver. 23.0 (IBM Co., Armonk, NY, USA). The normality of the data distribution was assessed with the Kolmogorov-Smirnov test. Nonparametric values were analyzed with the Wilcoxon test and parametric values with the t-test. A P-value less than 0.05 was defined as statistically significant.
In total, 21 subjects (10 boys and 11 girls) were included in the study. The mean age was 10.19±3.20 years. The RMS values could not be recorded in the sitting position in 5 patients due to a lack of cooperation. The mean RMS values at the supine and sitting positions are given in
The mean percentages of the differences between each channel were calculated (
Many studies have investigated the techniques of EMG examinations; however, few studies have described the reference electrode location [
EMG is an integral part of urodynamic studies. Disposable surface electrodes have been widely used for many years [
Bony prominences, hypothetically being electrically unaffected areas, have also been suggested as a better option for placing reference electrodes [
Although a urodynamic examination in a sitting position gives better results, supine urodynamics may be more ergonomic in patients with mobility impairments. Therefore, we evaluated the performance of EMG electrodes in different patient positions. Our study showed that the difference between different positions for each electrode was small.
The reliability of EMG studies is frequently questioned due to the lack of standardization in many aspects [
The record system setup was specifically designed with the following features to investigate the effects of the reference electrode position: Measurements from all locations with 4 identical EMG amplifiers through 4 simultaneous analog-to-digital conversion processes made it possible to analyze the same EMG signal in real time without any difference at the inputs except the reference electrode. The EMG amplifiers with electrically isolated inputs (
There are some limitations of this study. The results may not reflect clinically substantial differences since the RMS values were very similar. Placing a reference electrode on the skin over the gluteus may not affect the EMG results.
In conclusion, our study revealed that different options for reference electrode placement result in slight differences between EMG recordings. The knee is not a suitable option for placing the reference electrode. The AIS should be the preferred location for the reference electrode in the sitting position and the inner thigh in supine position during urodynamic studies. This information may help improve EMG recordings in the evaluation of pelvic floor muscles.
This study was supported by Ege University Scientific Research Projects Coordination Unit.
This study was approved by the local ethic committee of the Ege University Faculty of Medicine (19-11.1T/47).
No potential conflict of interest relevant to this article was reported.
·Conceptualization:
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Isolated amplifiers prevent interactions between electrodes.
Schematic diagram of the setup.
The general structure of the DASYlab program.
The location of the electrodes.
The mean percentages of the differences between each channel. RMS, root mean square; AIS, anterior iliac spine.
Mean RMS values in the supine and sitting positions
Reference localization | Mean RMS values in the supine position |
Mean RMS values in the sitting position |
||
---|---|---|---|---|
No. | Mean±SD | No. | Mean±SD | |
Knee | 21 | 0.89 ± 0.81 | 17 | 0.69 ± 0.28 |
Thigh | 21 | 0.98 ± 0.87 | 17 | 0.76 ± 0.29 |
AIS | 21 | 0.95 ± 0.75 | 17 | 0.79 ± 0.30 |
Gluteus | 21 | 0.98 ± 0.86 | 17 | 0.77 ± 0.29 |
RMS, root mean square; SD, standard deviation; AIS, anterior iliac spine.
Statistical significance of the mean RMS values according to the reference localization.
Localization | Supine position |
Sitting position |
---|---|---|
P-value (Wilcoxon test) | P-value (t-test) | |
Knee vs. thigh | 0.000 | 0.000 |
Knee vs. AIS | 0.010 | 0.000 |
Knee vs. gluteus | 0.000 | 0.000 |
Thigh vs. AIS | 0.217 | 0.000 |
Thigh vs. gluteus | 0.848 | 0.128 |
AIS vs. gluteus | 0.054 | 0.000 |
RMS, root mean square; AIS, anterior iliac spine.