Hypothesis / aims of study
Continence in males and females depends on smooth muscles, passive forces and the contribution of multiple striated muscles, which can all constrict the urethra at different locations. Comprehensive analysis of continence function would require simultaneous measurement of each contribution. Conventional urodynamic testing typically uses catheter devices with two pressure transducers; one located in the bladder and one located in the urethra , or a single pressure sensor that records pressure during withdrawal (i.e. conventional measure of maximal urethral closure pressure [MUCP]). There are several problems with these methods. The former lacks the spatial resolution to investigate how the multiple continence mechanisms simultaneously coordinate maintenance of urinary continence. It is also not possible to accurately identify the location of the urethral transducer, which may lie adjacent to different muscles in different patients or tests. Pressure recordings during catheter withdrawal assume that the mechanisms can maintain a constant pressure over the time taken to complete the withdrawal, which is an issue because the pelvic floor muscles have been shown to fatigue rapidly and this limits measurement to static tasks. Recently a multi-sensor pressure catheter has been developed that uses fibre-optic technology to measure pressure at multiple sites that extend the entire length of the urethra at intervals of 1 cm.
This initial study aimed to; (i) test the feasibility of recording urethral pressure using this new multi-sensor pressure catheter, (ii) provide preliminary data of one male and one female participant for calculation of the amplitude, location and timing of the increase in urethral pressure along the length of the urethra, and (iii) investigate the relationship between displacements observed on transperineal ultrasound imaging (US) and the urethral pressures recorded at sites related to specific muscles.
Study design, materials and methods
This proof of concept study included one male and one female participant aged 47 and 33 years, respectively. A multi-sensor fibre optic pressure catheter with sensors at 1-cm increments was inserted into the urethra using an aseptic technique. An ultrasound transducer (Aixplorer, Super Sonic Imagine, France) was placed on the perineum in the mid-sagittal line to measure displacement of landmarks associated with contraction of the striated urethral sphincter (SUS), puborectalis (PR) and bulbocavernosus (BC) muscles . Ultrasound imaging and pressure data were recorded simultaneously during sub-maximal and maximal voluntary contractions and coughing evoked by inhalation of capsaicin. Pressure data from each sensor was evaluated. Time of onset and peak pressures were identified and the change in amplitude with each task was recorded.
Increases in pressure were successfully recorded from all sensors simultaneously in all tasks in both participants, confirming the viability of the device for recording urethral pressure. Discrete regions of pressure increase could be attributed to PR, SUS, and BC. Onset of pressure increase occurred in a distal to proximal wave in the male participant (Fig. 1), but not the female participant during voluntary contraction. The location, timing and amplitude of peak urethral pressure varied between tasks in both participants. Coughing resulted in the greatest urethral pressure increase recorded across all tasks for both participants. Displacements measured from ultrasound imaging were correlated with pressure data.
Interpretation of results
The fibre optic catheter provided high spatial resolution pressure recordings in both participants. Patterns of pressure change differed along the urethra. This implies a non-uniform contribution of the individual striated muscles of the pelvic floor to constriction of the urethra and thus, continence control. Differences in the patterns of pressurization were observed between sexes and tasks.