Hypothesis / aims of study
Pressure changes within the vagina have historically been used to assess the effectiveness of a voluntary pelvic floor muscle (PFM) contraction. The perineometer, a balloon type device has been used extensively to determine ‘strength’ and ‘function’ of the pelvic floor. However, due the design of these devices, the pressure changes reflect global pressure change within the vagina, making it impossible to discriminate between an increase in abdominal pressure and that induced by PFM.
It is well recognised that a pressure profile exists along the vagina, and the mid (high) pressure zone corresponds to the anatomical location of the PFM (1). Measurement and display of this profile provides a more comprehensive and effective means of biofeedback to inform women whether they are performing effective voluntary PFM contractions. This information should thus be provided when using a biofeedback device for PFM training (PFMT).
femfit® (Figure 1) is an intravaginal biofeedback device, consisting of eight pressure sensors (positioned at 10 mm intervals), that measures the vaginal pressure profile (2). Simultaneous detection of different vaginal pressure zones enables the user to discriminate between abdominal and PFM pressures, and provide comprehensive biofeedback on PFMT technique.
The aim of this study was to investigate if a pressure sensor array is more effective at determining PFM contractions, and to understand which of the distal sensors measured peak PFM pressure when contracting in supine and upright positions.
Study design, materials and methods
This is a secondary analysis from a prospective interventional randomised pilot study of women with predominately stress urinary incontinence (leakage at least 3 times per week, over the last 3 months).
In the parent study, sixty participants were randomised into two groups. The biofeedback group used the femfit® system (device and mobile application) to complete PFMT (intervention) for twelve weeks. Non-biofeedback used the same mobile application and followed the same PFMT protocol as the biofeedback group, but did not but did not use a femfit® device (control).
A PFM physiotherapist completed blinded assessments of each participant. The femfit® was used to measure pressure generated by the pelvic floor during a voluntary maximal PFM contraction while supine, which was then repeated while upright (3 × 5 second contractions in each position). The physiotherapist inserted the femfit® to ensure it was positioned correctly for each participant. To minimise study bias, the physiotherapist did not provide guidance or encouragement to the participant on how to perform a contraction. These PFM contractions (as measured by the femfit®) captured PFM function characteristics.
This secondary analysis used descriptive statistics to investigate the sensor that detected peak PFM pressure (during maximal voluntary PFM contraction). Pressure data from distal sensors 1 to 6 (Figure 1) was used to identified peak PFM pressure for each PFM contraction in both supine and upright positions. When participants had the same sensor detect peak PFM pressure for at least two of their three PFM contractions (for that posture position), this was defined as the dominant sensor.
Results
A total of 99 voluntary maximal PFM contractions in supine, and 99 in the upright position were analysed from 33 study participants.
In the supine position, 28 women (85 %) had the same sensor detect peak PFM pressure for each of their three PFM contractions, indicating internal consistency. The remaining five women (15 %) had the same sensor detect peak PFM pressure for 2/3 of their contractions. Between participants, the most frequent dominant sensor was sensor 3 (33 %), followed by sensor 1 (18 %). Only one participant (3 %) had sensor 6 as their dominant sensor.
In the upright position, 22 women (67 %) had the same sensor detect peak PFM pressure for all three PFM contractions. Four participants (12 %) had the same sensor for 2/3 contractions, and two participants (6 %) had a different sensor for each of the three contractions. For the 31 participants with a dominant sensor, the most frequent sensor was sensor 6 (35 %), followed by sensor 1, 2 and 5 with five participants (16 %) each.
A summary of the dominant sensor spread between patients is given in Figure 2. Overall, the mean dominant sensor was sensor 3 in supine (SD: ±1.4) and sensor 4 in upright (SD: ±2.0). In supine, the median dominant sensor was sensor 3, while in upright the median was sensor 5.
When changing posture from supine to upright, seven participants (21 %) had the same sensor detect peak PFM pressure for all three contractions in both positions. For 11/31 participants (35 %), their dominant sensor while upright was adjacent to their dominant sensor in supine (e.g. sensor 1 in supine and sensor 2 in upright).
Interpretation of results
Overall, multiple distal sensors detected a peak PFM pressure during maximal voluntary PFM contraction. The vaginal pressure profile is likely to change dependent on posture, device placement, anatomical adjustment to an internal device and natural anatomical movement. The array of eight pressure sensors used in this study can accommodate this variation. This analysis highlights that a global pressure change (measured by a perineometer) would not capture the magnitude of PFM pressure generated during a voluntary PFM contraction, whereas a pressure sensor array can.
It is promising to see that, for the majority of women when performing repeated PFM contractions in the same position, femfit® detects peak PFM pressure in the same anatomical location, demonstrating the repeatability and reliability of the device.