Hypothesis / aims of study
Pelvic floor muscle training is recommended first line treatment to cure or improve symptoms of urinary continence and improve pelvic organ support [1]. Yet evaluation in the change in muscle function is often limited to subjective questionnaires, or specialised measures of morphometry and function such as ultrasound imaging, or instrumentation that is only available in a research setting. femfit®, a thin and flexible intravaginal pressure sensor array [2], offers an objective, precise, and user-friendly method for quantifying pelvic floor muscle function. It does so by measuring the vaginal pressure profile, through eight sensors located along the length of the device, thus measuring pelvic floor and abdominal pressure simultaneously [3]. The device transmits and visualises pressure data wirelessly on a mobile app in real-time. The performance metric, derived from the profile generated, is named pelvic floor muscle activation pressure (PFMA). It is the difference between pelvic and intra-abdominal pressure, taking into account that the goal during voluntary pelvic floor muscle contractions is to achieve high pressure in the region of the pelvic floor muscles, while keeping abdominal pressure low. The higher the PFMA, the better. For instance, a PFMA score of 8 indicates a peak pelvic floor pressure of 10 mmHg and an intra-abdominal pressure of 2mmHg, suggesting stronger pelvic floor activation compared to a PFMA of 2, which would equate to peak pelvic pressure of 10mmHg and an intra-abdominal pressure of 8mmHg.
The assessment with femfit® formed part of a larger ongoing study, The Clinical Prediction Rule Trial (CER VN 17-18-17), investigating effectiveness of pelvic floor muscle training in women with stress urinary incontinence (SUI) and identifying predictors of success.The aim of this subanalysis was to investigate changes in PFMA calculated from femfit® in women with SUI before and after participating in a validated 12-weeks pelvic floor muscle training (PFMT) programme. The null hypothesis is that the difference between the pre and post PFMA scores in women with UI is zero.
Study design, materials and methods
Participants were recruited through advertisement in the community, inclusion criteria were women > 18 years; have SUI or mixed urinary incontinence (MUI) with predominant stress symptoms (based on QUID), have at least 3 UI episodes in the 7-day bladder diary; are ambulatory. Exclusion criteria included women with urge UI; have any acute or chronic risk factors, medical problems or take medication likely to interfere with the PFMT or evaluations; The assessment time points before and after the 12 week programme were facilitated by a physiotherapist, who also inserted femfit® for each participant. None of the participants reported discomfort or pain during the use of femfit®. Participants were asked to rest for 30 seconds, perform 3 voluntary pelvic floor muscle contractions with 15 seconds rest in between each contraction. Figure 1 shows an example of a participant's post session pressure profile (PFMA = 9.29), with the offset pressures removed from each sensor to ensure only the changes in pressure related to muscle activation were analysed.
A PFMA score was calculated for each participant's pre and post assessments. This was achieved by identifying the peak pressures during each contraction, calculating a median from these peaks, and then averaging the results from the three contractions. This process provided an overall peak pressure value for each sensor. Sensor 8 was taken as the abdominal sensor, whereas the sensor with the highest mean pressure of all contraction peaks from sensor 1 to sensor 7 was taken as the pelvic floor sensor. In the example session presented in Figure 1, the pelvic sensor used is sensor 5. PFMA is then calculated by the mean peak pressure from the pelvic floor sensor minus the mean peak pressure from the abdominal sensor.
Wilcoxon signed-rank test was performed to test the null hypothesis, as the data is not normally distributed. Participants also completed ICIQ-UI Questionnaire, leakage diary before and after the training programme. A patient-estimated percentage symptom improvement was asked after completion of the programme. One-sided Wilcoxon signed-rank tests were conducted on subsets of participants who have shown clinically important improvement: 4 or more point decrease in ICIQ-UI questionnaire; and improvement in leakage dairy score with 50% or more, patient-estimated percentage improvement of 50% or more.
Results
43 participants were initially recruited for the study, of which 24 had femfit® pressures recorded before and after the PFMT programme for analysis. Mean age was 58 years (range 33 - 80), mean BMI 29.2 kg/m2 (range 22.2 - 43.9), median parity 2 (range 0 - 4). Results of pre and post PFMA scores for the 24 participants are shown in Figure 2.
For this study, the difference in PFMA scores before and after the intervention was not statistically significant (p = 0.0951) at the 0.05 significance level, with pseudo median difference (post to pre) being 1.73. The null hypothesis that the median difference is zero cannot be rejected. For the one-sided Wilcoxon signed-rank tests done on subsets of the data, the results are as follows: for participants with an ICIQ-UI improvement of 4 points or more (n=13), pseudo median difference is 0.87 (p = 0.2709); for those with a leakage improvement of 50% or more (n=15), pseudo median difference is 1.12 (p = 0.2271); and among those with an patient-estimated percentage improvement of 50% or more (n=20), pseudo median difference is 1.49 (p = 0.0615).
Interpretation of results
This novel performance metric of PFMA provides a comprehensive representation of the overall functionality of pelvic floor muscles in a simple single number while considering both the pelvic and intra-abdominal pressures. This approach also helps avoid potentially misleading results that may arise when using only the maximum pelvic pressure. Although the differences found in this study were not statistically significant, considering that the PFMA is a summary of two factors and the small sample size, this is likely due to a type 2 error. In general, there’s a noteworthy positive improvement in PFMA following a valid 12-week PFMT programme in women that warrants further investigation in larger studies.