Electrical Implants for the Neuropathic Bladder Flashcards
Function of cerebral cortex
Conscious control of voiding
Function of pontine micturition centre
Co-ordination of bladder and sphincter contraction/relaxation
Function of sacral micturition centre
Detrusor contraction
Function of parasympathetic nerves
S2-S4 run in pelvic nerve
Detrusor contraction
Function of sympathetic nerves
- T11-L2 run through hypogastric plexus
- detrusor relaxation/sphincter relaxation
Function of somatic nerves
- pudendal nerves arising in Onuf’s nucleus
- sphincter contraction
What happens in the storage phase?
- afferent impulses from stretch receptors to spinal cord
- sympathetic efferents inhibit the detrusor and contract the internal sphincter
- somatic efferents (pudendal nerve) contract the external urethral sphincter
What happens in the voiding phase?
- afferent impulses from stretch receptor to pons
- PMC activated if not inhibited by higher centres
- parasympathetic efferents (S2-S4) contract detrusor muscle
- sympathetic efferents relax bladder neck
- somatic efferents inhibited, external urethral sphincter relaxes
What is the bladder function after SCI
- interrupted normal control of bladder function blocking pathway between bladder and higher centres
- function depends on level of injury
- loss of voluntary control and development of aberrant reflexes that are not inhibited
Presentation of Upper Motor Neurone Lesion Bladder Dysfunction
- lesion above SMC
- bladder reflexes intact
- loss of conscious control
- loss of co-ordination
- detrusor over activity
- detrusor sphincter dys-synergia
- autonomic dysreflexia
Lower motor Neurone Lesion Bladder Dysfunction
- lesion below SMC
- areflexic bladder and sphincters
- loss of conscious control
How/Why does loss of conscious control present in an UMN lesion?
- no voluntary bladder emptying
- lack of sensation of bladder fullness
Why is detrusor over activity in UMN lesions a problem?
- small capacity bladder
- reduced compliance
- incontinence
- high pressures = danger to upper tracts
Why is DSD in UMN lesions a problem?
- high pressures
- incomplete empyting, infection
How/Why does loss of conscious control present in an LMN lesion?
- no voluntary bladder emptying
- no sensation of bladder fullness
Why is weak sphincters and pelvic floor a problem in LMN lesions?
- incontinence/ stress/ overflow
Why is an areflexic bladder a problem in LMN lesions?
- large capacity bladder
- chronic retention
- poor compliance
What does management of the bladder after SCI aim to do?
- reduce pressures = protect upper tracts
- facilitate emptying
- improve capacity
- reduce incontinence
- improve quality of life
What management options are there for the bladder after SCI? What do they do?
- antimuscarinics, Botox injections = reduce pressures
- SPEC, ICS, urethral stenting, alpha blockers = allows emptying
- clam ileocystoplasty = improves capacity
- increase sphincter strength, AUS = reduce incontinence
FES for restoring bladder function
- alternative option
- control bladder by exploiting neuronal circuits
- current state of the art
How does FES work?
Exploit neuronal circuits:
- voiding phase (promotes bladder emptying via neurostimulatiion)
- storage phase (reduces pressure and increasing capacity via neuromodulation)
Sites for FES of the bladder
- bladder wall
- sacral nerve roots (intra-thecal and extradural)
- pelvic nerves
- hypogastric nerves
- spinal cord stimulation
- pudendal nerves
- pelvic floor
- tibial nerves
What is Intra-vesical Electrical Stimulation? How does it work?
- stimulating bladder mechanoreceptor afferents
- catheter mounted electrode (cathode) placed in urethra
- anode electrode on abdominal skin over pubic symphysis
What has intra-vesical electrical stimulation been used for?
- children with underactive bladder due to spina bifida and hypo- or acontractile bladder in SCI
- reports that it increased ability to empty bladder
- however best results in hypocontractile bladder
Detrusor muscle stimulation Challenges
- difficult to keep electrodes in place over long period
- concomitant contraction of external urethral sphincter due to stimulation of sensory nerves
- high stimulation currents required
Pelvic nerve stimulation challenges
- lower currents required
- difficult to access nerves
- concomitant contraction of EUS
Finetech Sacral Anterior Root Stimulator (SARSI)
- implant restoring bladder function following SCI
- electrodes placed on S2-S4 roots
- intra-thecal or extra-dural
- electrical stimulation (20-40Hz) causing bladder contraction
- complete bladder emptying w/o need for catheters
- usually combined with posterior rhizotomy to reduce over-activity
Parts of sacral anterior root stimulator implant (SARSI)
- external control unit
- external cable
- transmitter block
- receiver block
- implanted cable
- electrodes
Benefits of SARSI with posterior rhizotomy
- complete bladder emptying with low residual
- posterior rhizotomy
- increased bowel function
- implant driven erections
Why is complete bladder empyting with low residual an advantage with SARSI + posterior rhizotomy
- reduction in bladder infections
- eliminates need for catheters
Why is increased bowel function an advantage with SARSI + posterior rhizotomy
- increases bowel motility, moving stools down colon
- in some patients evacuation occurs by stimulation alone
Why is posterior rhizotomy an advantage?
- eliminates reflex incontinece
- improved bladder compliance
- reduces autonomic dys-reflexia (associated with bladder)
- protects from kidney failure
Sacral Nerve Neuromodulation
- medtronic interstim targets sacral afferents entering spinal cord to modulate bladder reflexes reducing overactivity
- tined electrodes placed on extra-dural sacral S3 nerves
- implanted pulse generator
- best results in OAB
- early intervention in SCI reduced development of over activity
Percutaneous Tibial nerve Stimulation
- tibial nerve originates in L4-S3 lumbosacral plexus
- stimulation thought to cause neuromodulation of bladder reflexes
- less invasive than SNM
- treatment given for 30 mins 1-2 times a week
- used in OAB, MS, SCI
- best results in SCI
- may employ supra-spinal pathways
- no large acute studies in SCI
Spinal cord stimulation
- good results in animal models
- high complication rates
- epidural electrodes now being developed for locomotor function
- improved bladder function anecdotally reported
- transcutaneous spinal cord stimulation
Pudendal nerve stimulation
- originates at S2-S4 of spinal cord
- low frequency electrical stimulation (5-15Hz) of the pudendal nerves has been shown to effectively suppress bladder over activity
- distally (dorsal genital nerve) becomes purely afferent
- improved results compared with neuromodulation of whole sacral root
High Frequency Nerve Blocking
- high freq electrical stimulation (kHz range) of pudendal nerves can block motor axons to sphincter
- possibility of reducing DSD and concomitant sphincter contraction during bladder stimulation
- LT safety on human nerves not yet determined
Past, Current and Potential Research at RNOH
- SPARSI and SPAIRS
- Surface Neuromodulation
- Wearable devices
- Pudendal blocking
- Complete bladder function restoration
SPAIRS
- sacral nerve neurostimulation through Finetech SARS
- no sacral de-afferentation
- sacral neuromodulation through sacral electrodes
What does sacral neuromodulation through sacral electrodes do?
- extra-dural electodes (mixed nerve root) could not empty bladder due to reflex contractions of sphincter = need to block sphincter contraction
- intra-thecal electrodes seperated motor and sensory nerves so could provide differentiated stimulation?
Optimization of neuromodulation site
- dorsal gential nerve
- tibial nerve
- sacral spinal cord
CARM
- wearable neuromodulation
- conditional ano-rectal modulation
- provides trans-anal neuromodulation to pudendal nerves lying in Alcock’s canal
- neuromodulation triggered conditionally on increase in sphincter EMG
- trial in 6 SCI patients gave significant increase in bladder capacity and reduction in pressure
- improved design
- further clinical trials
Complete restoration of bladder function
- bladder emptying by stimulation of anterior roots
- prevention of DSD by pudendal nerve blocking
- conditional neuromodulation of NDO by pudendal nerve stimulation
