Genital nerve stimulation increases bladder capacity after SCI: A meta-analysis

Abstract

Background: Neurogenic detrusor overactivity (NDO) often results in decreased bladder capacity, urinary incontinence, and vesico-ureteral reflux. NDO can trigger autonomic dysreflexia and can impair quality of life. Electrical stimulation of the genital nerves (GNS) acutely inhibits reflex bladder contractions and can increase bladder capacity. Quantifying the effect of GNS on bladder capacity and determining what study factors and subject factors influence bladder capacity improvements will inform the design of clinical GNS interventions.

Methods: We measured bladder capacity in 33 individuals with NDO, with and without GNS. These data were combined with data from seven previous GNS studies (n=64 subjects). A meta-analysis of the increase in bladder capacity and potential experimental factors was conducted (n=97 subjects total).

Results: Bladder capacity increased 131±101 ml with GNS across subjects in all studies. The number of individuals whose bladder capacity was greater than 300 ml increased from 24% to 62% with GNS. Stimulus amplitude was a significant factor predicting bladder capacity gain. The variance of the bladder capacity gain significantly increased with increasing infusion rate. Other factors did not contribute to bladder capacity gain.

Conclusion: GNS acutely increases bladder capacity in individuals with NDO. The consistent increase in magnitude of bladder capacities across the eight studies, and the lack of dependence on individual-specific factors, provide confidence that GNS could be an effective tool for many individuals with NDO. Studies of the chronic effect of GNS on bladder control, with clinical measures such as urinary continence, are needed.

Keywords: Electrical stimulation; Genital nerve stimulation; Neurogenic bladder; Spinal cord injury.

Figures

Figure 1

Bladder capacities increased from a baseline of 284 ± 148 ml (control) to 432 ± 179 ml (stimulation) in response to GNS (n = 33) in the current Bourbeau et al. cohort (P<0.001). The boxplot shows the 10th, 25th, 50th, 75th, and 90th quartiles for the distributions of bladder capacities without and with stimulation. Genital nerve stimulation (GNS) achieved Bladder Capacity Gains of 148 ± 97 ml. This increase in bladder capacity is the primary outcome measure used for the meta analysis.

Figure 2

Bladder capacity gains and 95% confidence intervals are shown for the current study and seven other studies (n = 97 subjects total). Mean Bladder Capacity Gain for all subjects (n = 97) was 131±101 ml (108 – 155 95% confidence interval). Bourbeau et al. are data from the current study and shown in Figure 1. These data provide confidence in the amount and variance for improvements in bladder capacity from GNS. No studies were statistically different from the pooled mean. The consistency of the bladder capacity gain across multiple studies suggests that GNS may be effective for the majority of individuals with SCI and NDO.

Figure 3

The distribution of bladder capacities achieved with genital nerve stimulation (GNS) increased. Most individuals reached clinically acceptable bladder capacities. Bladder capacity increased by at least 50 ml in 79/97 (81%) of individuals. The number of individuals whose bladder capacity was greater than 300 ml increased from 23/97 (24%) to 60/97 (62%) with GNS. 400 ml: 11/97 (11%) to 33/97 (34%). 500 ml: 2/97 (2%) to 23/97 (24%).

Figure 4

Increasing bladder infusion rates during urodynamic studies increased the variance of the Bladder Capacity Gains by 0.014 ml/(ml/min). Data are grouped by study cohort (n = 8). Infusion rate did not affect the magnitude of the Bladder Capacity Gain. Therefore, larger infusion rates may increase the standard deviation, or precision, of the measured Bladder Capacity Gain and may affect statistical power.