Conditional and continuous electrical stimulation increase cystometric capacity in persons with spinal cord injury

Abstract

Aims: Individuals with spinal cord injury (SCI) exhibit neurogenic detrusor overactivity (NDO) causing high intravesicle pressures and incontinence. The first aim was to measure changes in maximum cystometric capacity (MCC) evoked by electrical stimulation of the dorsal genital nerve (DGN) delivered either continuously or conditionally (only during bladder contractions) in persons with SCI. The second aim was to use the external anal sphincter electromyogram (EMG(EAS)) for real-time control of conditional stimulation.

Methods: Serial filling cystometries were performed in nine volunteers with complete or incomplete supra-sacral SCI. Conditional stimulation was delivered automatically when detrusor pressure increased to 8-12 cmH(2)O above baseline. MCCs were measured for each treatment (continuous, conditional, and no stimulation) and compared using post-ANOVA Tukey HSD paired comparisons. Additional treatments in two subjects used the EMG(EAS) for automatic control of conditional stimulation.

Results: Continuous and conditional stimulation increased MCC by 63 +/- 73 ml (36 +/- 24%) and 74 +/- 71 ml (51 +/- 37%), respectively (P < 0.05), compared to no stimulation. There was no significant difference between MCCs for conditional and continuous stimulation, but conditional stimulation significantly reduced stimulation time (174 +/- 154 sec, or 27 +/- 17% of total time) as compared to continuous stimulation (469 +/- 269 sec, 100% of total time, P < 0.001). The EMG(EAS) algorithm provided reliable detection of bladder contractions (six of six contractions over four trials) and reduced stimulation time (21 +/- 8% of total time).

Conclusions: Conditional stimulation generates increases in bladder capacity while substantially reducing stimulation time. Furthermore, EMG(EAS) was successfully used as a real-time feedback signal to control conditional electrical stimulation in a laboratory setting.

Fig. 1

Cystometrograms in a person with spinal cord injury with no stimulation, continuous stimulation, and intermittent stimulation of the dorsal genital nerve. Top three traces display detrusor pressure during no, continuous, and conditional stimulation treatments, with cystometric capacities marked on the bottom trace of infused volume (circle: no stimulation, 271 mL; triangle: continuous stimulation, 483 mL; square: conditional stimulation, 534 mL). The thick horizontal lines denote the delivery of 15 Hz stimulation, asterisks denote stimulation-suppressed contractions, and cross denotes unsuppressed contraction during the conditional stimulation treatment. The transient dips in detrusor pressure were caused by fluctuations in abdominal pressure (not shown).

Fig. 2

Average cystometric capacity during cystometry with no stimulation, continuous stimulation, and conditional stimulation. Open points are individual subjects, solid points are population means, and error bars show standard deviations. Asterisks denote significant difference between groups.

Fig. 3

Analysis of cystometric capacity by trial number (1=first trial, 2=second trial, etc.). The plot displays cystometric capacities for each trial (diamonds: wide, no stimulation; narrow, continuous stimulation; barred, conditional stimulation), the mean cystometric capacity within each trial number group (crosses), and the overall mean (line). There was no significant correlation between cystometric capacity and trial number (Spearman’s rank). Furthermore, the average cystometric capacity during the first trials (always baseline) was not significantly different from the average of other no stimulation trials (Student’s t-test).

Fig. 4

A: Example cystometrogram during a conditional stimulation treatment displaying four suppressed detrusor contractions (asterisks). The fifth contraction (cross) was not suppressed completely, possibly due to the pause in stimulation (arrowhead). B: Transient detrusor contractions (arrowhead) appeared in two of 20 continuous stimulation treatments and in one control treatment. An uncontrolled detrusor contraction (cross) determined the cystometric capacity (33 mL @ second 100).

Fig. 5

Closed-loop electrical control of continence. An adaptive threshold algorithm was used to detect hyper-reflexive detrusor contractions and trigger conditional stimulation (gray bars) in a real-time implementation of closed-loop control of urinary continence. Four false positive (1, 2, 3, 4) and two true positive detections (5, 6) were triggered by the algorithm. Magnification displays the external anal sphincter electromyogram (EAS EMG), detection signal, and adaptive threshold during the fifth detection. Pdet: detrusor pressure.