Hypothesis / aims of study
This study aimed to assess the acute effects of TTNS on OAB through invasive urodynamics (UDI), using an intermittent, on-demand approach; with a focus on urinary urgency as the central axis for its application
Study design, materials and methods
A proof of concept was carried out on patients, with OAB. Included were subjects with a negative urine culture, excluding those with previous TTNS treatments or recent antimuscarinic use.
After informed consent, approved by the local ethics committee, a standard invasive UDI was performed, following the recommendations of the International Continence Society Good Urodynamic Practices.(1)
Patients who presented with detrusor overactivity (DO) associated with urgency during cystometry were selected. Patients who did not meet these two conditions, or with low bladder compliance (BC) were excluded (≤20ml/cmH2O)
Those selected were immediately subjected to a second cystometry (UDI TENS), this time connected to a Transcutaneous Electrical Nerve Stimulation (TENS) device positioned at the stimulation points of the posterior tibial nerve in normal mode, with a frequency of 30 Hz and a pulse width of 200 microseconds. Correct electrode placement was verified by observing toe flexion produced by the contraction of plantar muscles in response to the TENS device stimulus. The intensity for application was determined based on the motor stimulation level and the absence of painful sensation.
During the second cystometry, TTNS stimulus was initiated each time the patient indicated the onset of urgency, and it was stopped when the patient reported relief of this symptom.
Both urodynamics were performed in the sitting position. Intravesical pressures were measured with a fluid-filled double-lumen 6 Fr catheter. For abdominal pressures, a rectal flaccid-filled balloon catheter was used. The external transducers were calibrated to atmospheric pressure, using the upper edge of the symphysis pubis as a reference. Data were integrated into the Laborie Aquarius Lt. equipment. A non-physiological filling rate of 40-50 ml per minute with normal saline at room temperature was used for cystometry.The infusion was stopped when the patient expressed a strong desire to void, or a terminal involuntary detrusor contractions occurred.
During UDI Dg, involuntary detrusor contractions (IDC), maximum cystometric capacity (MCC), urgency urinary incontinence episodes (UUI), were noted, bladder compliance (BC) was calculated. The average duration of the involuntary detrusor contractions was determined by calculating the mean duration of each contraction, excluding terminal contractions.
During UDI TENS, in addition to the previous parameters, TENS device activations (ACT) were noted, and the average duration of the ACT time was calculated.
Statistical analysis was performed using the Shapiro-Wilk test and Student's t-test or the Wilcoxon test as appropriate, with significance set at p ≤ 0.05.
Results
The study initially involved a total of 29 subjects, including 25 women and 4 men. After the first cystometry, 17 subjects were excluded and did not proceed to the second cystometry. Among these, 11 did not exhibit DO. One patient requested to discontinue, one had previously consumed antimuscarinics, and four had a BC of ≤ 20 ml/cm H2O.
For the second cystometry, 12 subjects were selected, comprising 2 men and 10 women, with an average age of 53 years, ranging from 23 to 81 years. The etiology of OAB in three cases was secondary to Bladder Outlet Obstruction (BOO); one case was associated with Genitourinary Syndrome of Menopause (GSM); one with Coexistent Overactive-underactive Bladder Syndrome (COUB); one with Painful Bladder Syndrome (PBS); and six were idiopathic or under investigation without an apparent neurological cause.
During UDI Dg, an average of 3.33 ± 1.3 IDCs per patient were observed, with episodes of UUI averaging 0.67 ± 0.98. Meanwhile, the MCC reached 235 ± 79 ml, and the average duration of IDCs was 33 ± 19 seconds. In contrast, during conditional UDI TENS, a decrease in the number of IDCs to an average of 0.08 ± 0.29 (p ≤ 0.001) and an absence of UUI episodes were recorded. An increase in MCC to 315 ± 83 ml (p = 0.00012) was observed. The number of ACTs was 5.25 ± 2.56, with an average duration of 26 ± 10 seconds. (Figure 1 summarizes the main events per patient in each urodynamics sesión)
Following each device activation, patients reported a significant decrease in the intensity of urinary urgency. To evaluate if there was also an effect on the duration of the urgency sensation, we compared the average duration of IDCs versus ACTs. Although the latter was shorter (26 ± 10 vs 33 ± 19 seconds), this difference did not reach statistical significance (p = 0.33).
Interpretation of results
In this series of patients, we observed through UDI that the application of acute TTNS stimulus, using an intermittent, on-demand approach, effectively reduces the intensity of urinary urgency, the number of IDCs, the number of UUI episodes, and improves MCC in patients with OAB.
While a favorable response in terms of reducing the urgency sensation's duration was observed, certain errors in the study design, such as the failure to record urgency episodes without an increase in true detrusor pressure during the first cystometry, hamper a correct data analysis in this aspect.
Despite the heterogeneity of the group in terms of sex, age range, and comorbidities, detrusor stability during the fill phase was achieved in the vast majority . This stability also extended to controlling urge urinary incontinence episodes, (figure 2) with significant improvement even observed in the patient who presented with DO during UDI TENS (figure3). These findings suggest that TTNS could influence the triggering mechanism of IDCs, regardless of the syndrome's underlying etiology.
Furthermore, these observations allow us to infer that the sensation of urinary urgency generally precedes the IDC; this reinforces the theory that urinary urgency in OAB is more a reflection of altered neuromuscular activity than a consequence of increased vesical pressure itself.
Available studies indicate that consecutive cystometries can affect urodynamic parameters in patients with OAB, potentially reducing DO (2). This finding contrasts with a 2010 study aimed at assessing the reproducibility of repeated urodynamic measurements within the same session in women with incontinence, where the authors concluded that the reproducibility of these measurements was good to excellent.(3) Furthermore, these findings align with current guidelines.(1)
Comparing our results with others in the literature is challenging due to differences in the studied populations, as well as in the techniques and stimulation patterns employed. Amarenco (2003) and Canbaz (2008, 2009) provided evidence of the effectiveness of PTNS and TTNS with a continuous stimulation approach. In contrast, other research, like Doherty (2019), did not find TTNS effective in inhibiting IDCs with conditional stimulation in a population with spinal cord injuries. These discrepancies underscore the need for deeper and more systematized exploration to fully understand TTNS's impact on OAB.
Concluding message
Our study presents promising results regarding the ability of TTNS to acutely reduce DO, decrease the episodes of UUI, and increase the MCC in patients diagnosed with OAB using intermittent, conditional, on-demand approaches. However, the limited number of patients analyzed suggests that these findings should be interpreted with caution. This underscores the need for additional research involving a larger sample of patients and the inclusion of a control group to more definitively corroborate our findings