Study design: Laboratory investigation using serial slow-®ll cystometrograms. Objectives: To examine the acute e ects of di erent modes of dorsal penile nerve stimulation on detrusor hyperre¯exia, bladder capacity and bladder compliance in spinal cord injury (SCI). Setting: Spinal Injuries Unit, Royal National Orthopaedic Hospital, Stanmore, Middlesex, UK. Methods: Fourteen SCI patients were examined. Microtip transducer catheters enabled continuous measurement of anal sphincter, urethral sphincter and intravesical pressures. Control cystometrograms were followed by stimulation of the dorsal penile nerve at 15 Hz, 200 ms pulse width and amplitude equal to twice that which produced a pudendo-anal re¯ex. Stimulation was either continuous or in bursts of one minute triggered by a rise in detrusor pressure of 10 cm water (conditional). Further control cystometrograms were then performed to examine the residual e ects of stimulation. Results: Bladder capacity increased signi®cantly during three initial control ®lls. Continuous stimulation (n=6) signi®cantly increased bladder capacity by a mean of 110% (+Standard Deviation 85%) or 173 ml (+146 ml), and bladder compliance by a mean of 53% (+31%). Conditional stimulation in a di erent group of patients (n=6) signi®cantly increased bladder capacity, by 144% (+127%) or 230 ml (+143 ml). In the conditional neuromodulation experiments, the gap between suppressed contractions fell reliably as bladder volume increased, and the time from start of stimulation to peak of intravesical pressure and 50% decline in intravesical pressure rise was 2.8 s (+0.9 s) and 7.6 s (+1.0s) respectively. The two methods of stimulation were compared in six patients; in four out of six conditional neuromodulation resulted in a higher mean bladder capacity than continuous, but the di erence was not signi®cant. Conclusions: Both conditional and continuous stimulation signi®cantly increase bladder capacity. The conditional mode is probably at least as e ective as the continuous, suggesting that it could be used in an implanted device for bladder suppression. Spinal Cord (2001) 39, 420 ± 428

1. Somatosensory evoked potentials from electrical stimulation of the digital nerves of the right thumb have been recorded during the performance of various motor tasks in eight normal subjects. 2. The N20-P30 primary cortical response is only moderately affected by task context, while the P45-N55 secondary response is markedly 'gated' by movement of the stimulated digit. The late N140 vertex is variable. 3. In most subjects, active and passive movements are about equally effective in suppressing the secondary complex; but in one, passive movement has come to be rather less effective than active. 4. Secondary response suppression occurs in proportion to the velocity of the movement of the thumb, up to a velocity of 20 deg/s. 5. Secondary response suppression is unrelated to load in the range 0 to 0.16 Nm. 6. When the stimulus is timed to occur at various points in movement, secondary complex suppression occurs at all stages; but there is little or no suppression when stimulation is timed at 200 ms before the start of or 500 ms after the end of a movement. 7. Secondary response suppression is maximal when the same digit is both moving and shocked. When the right index or little finger are moved instead, the right thumb being stimulated, suppression is less; when the left thumb moves, no suppression is seen. 8. Secondary response suppression is reduced but not lost if the skin and interphalangeal joint of the thumb are anaesthetized distal to the stimulating electrodes. 9. Secondary response suppression is unimpaired when the radial nerve is anaesthetized, paralysing the finger extensors. 10. In an attempt to identify the course taken by the afferent volley between the primary and secondary responses, and to identify the gating site, we recorded the responses in six patients with Parkinson's disease who had undergone thalamotomy. Their secondary responses were present, and gated in the normal way. 11. We are unable to confirm whether the secondary response represents the re-arrival at cortical level of a volley that has traversed the cerebrocerebellar loop. 12. We confirm that the secondary complex is located a little anterior to the primary cerebral response. 13. We conclude that a gating action is exerted in the brain on somatosensory afferent activity, after it first reaches the cortex, and that this gating action associated with movement is controlled by other afferent signals from the stimulated limb, and particularly from the stimulated digit.

Study design: Investigation of ®ve patients receiving an implant, using laboratory cystometry and self-catheterisation at home. Objectives: To use the established Finetech-Brindley sacral root stimulator to increase bladder capacity by neuromodulation, eliminating the need for posterior rhizotomy, as well as achieving bladder emptying by neurostimulation. Setting: Spinal Injuries Unit, Royal National Orthopaedic Hospital, Stanmore, Middlesex, UK. Methods: Five patients underwent implantation of a Finetech-Brindley stimulator without rhizotomy of the posterior roots. This was either a two channel extradural device (four cases) or a three channel intrathecal device (one case). In each patient, the implant was con®gured as a Sacral Posterior and Anterior Root Stimulator (SPARS). Postoperatively, repeated provocations using rapid instillation of 60 ml saline were used to determine the relative thresholds for neuromodulation using each channel. The eect of continuous neuromodulation was examined in the laboratory using slow ®ll cystometrograms, and conditional stimulation was also studied (neuromodulation for 1 min to suppress hyperre¯exic contractions as they occurred). In one patient, neuromodulation was applied continuously at home, and volumes at self catheterisation recorded in a diary. Results: Re¯ex erections were preserved in each patient. In three patients, detrusor hyperre¯exia persisted postoperatively and neuromodulation via the implant was studied. In these three patients, the con®guration was: S2 mixed roots bilaterally (channel B), and S34 bilaterally (channel A). Both channels could be used to suppress provoked hyperre¯exic contractions, with the S2 channel eective at a shorter pulse width than S34 in a majority of cases. Continuous stimulation more than doubled bladder capacity in two out of three patients during slow ®ll cystometry. Conditional stimulation was highly eective. In the one patient who used continuous stimulation at home, bladder capacity was more than doubled and the eect was comparable with anticholinergic medication. Bladder pressures 470 cm water could be achieved with intense stimulation in three patients, but detrusor-external urethral sphincter dyssynergia (DSD) prevented complete emptying. Conclusions: Neuromodulation via a SPARS was eective and may replace the need for posterior rhizotomy. However, persisting DSD may prevent complete bladder emptying and warrants further investigation.

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