Acute phase spinal cord injury (SCI) induces urinary retention, whereas during chronic phase detrusor overactivity and detrusor sphincter dyssynergia (DSD) are observed [1]. Low-intensity extracorporeal shock wave therapy (LiESWT) has been used to treat orthopedic injuries, angina pectoris, and erectile dysfunction. LiESWT was recently shown to promote tissue regeneration in the vagina and urethra and ameliorate urinary dysfunction in an animal model of urinary disturbances such as stress urinary incontinence [2]. To date, the effect of LiESWT on the urethra after SCI, especially on DSD, remains unclear. To evaluate the efficacy of LiESWT in bladder and urethral dysfunction after SCI, we treated an SCI rat model with LiESWT and assessed its effects via cystometrogram (CMG) and external urethral sphincter electromyogram (EUS-EMG).

Seventeen female Sprague-Dawley rats, 6 weeks of age, were used in this study. SCI rats were produced by Th9 transection. Rats with induced spinal injury were divided into two groups: LiESWT treated (LiESWT group, n = 9) and LiESWT untreated (control group, n = 8). In the LiESWT group, LiESWT was performed at 3 weeks after spinal cord transection with an energy flux density of 0.12 mJ/mm2, 300 shots at 2 Hz, repeated four times, 1,200 shots in total. A shockwave applicator was applied to the lower abdomen and aimed at the bladder and urethra. Six weeks after spinal cord transection, CMG was performed to evaluate single voided volume, post-void residual volume, non-voiding bladder contractions, bladder contraction duration (CD) during voiding, and voiding efficiency (VE) under waking conditions in both groups. VE was calculated using the following formula: VE (%) = [voided volume /(voided volume + post-void residual volume) × 100]. EUS-EMG was performed to assess DSD by EUS-relaxation (EUS-R) and EUS-contraction (EUS-C) during voiding bladder contraction. The EUS-R ratio was calculated using the following formula: EUS-R ratio (%) = [EUS-R/CD × 100]. CD was defined as the duration of EUS-R + EUS-C (Figure 1). Each parameter was compared using the Mann–Whitney U-test, and P < 0.05 defined as significant.

In the CMG, voiding pressure amplitude and non-voiding bladder contractions were not significantly different between the control and LiESWT groups. However, VE was significantly higher in the LiESWT group than that in the control group (71.18 ± 6.64% vs. 51.76 ± 6.72%, P < 0.05).  Simultaneous CMG and EUS-EMG recordings showed that bladder contraction duration (CD) tended to be longer in control group than in LiESWT group (37.52 ± 5.74 sec vs. 26.25 ± 4.86 sec, p = 0.083). The total EUS-R-to-CD ratio was significantly higher in the LiEWST group than in the control group (66.16 ± 5.68% vs. 45.65 ± 3.98%, p < 0.05, Figure 1, Table 1).

These findings reveal that VE was significantly increased by LiESWT in rats with SCI. Amplitude voiding pressure (AVP) was higher and bladder contraction duration (CD) was longer in the control group, suggesting that urethral pressure, rather than bladder contractility, affects VE. The treatment of SCI rats with LiESWT resulted in an increase in the total EUS-relaxation to CD ratio and suppressed EUS activity during voiding. Hence, LiESWT reduced the DSD in rats with SCI.

The present study demonstrated the efficacy of LiESWT in the urethra by suppressing DSD, resulting in the improvement of VE. Therefore, LiESWT may be a promising approach to treat urinary dysfunction after SCI.

W. C. de Groat and N. Yoshimura, “Plasticity in reflex pathways to the lower urinary tract following spinal cord  injury.,” Exp Neurol, vol. 235, no. 1, pp. 123–132, May 2012, doi: 10.1016/j.expneurol.2011.05.003.
X. Zhang et al., “Delayed Treatment With Low-intensity Extracorporeal Shock Wave Therapy in an  Irreversible Rat Model of Stress Urinary Incontinence.,” Urology, vol. 141, pp. 187.e1-187.e7, Jul. 2020, doi: 10.1016/j.urology.2020.03.035.

Continence 7S1 (2023) 100968
DOI: 10.1016/j.cont.2023.100968