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Bioengineering in Urology > Electrical Implants for the Neuropathic Bladder > Flashcards

Electrical Implants for the Neuropathic Bladder Flashcards

1
Q

Function of cerebral cortex

A

Conscious control of voiding

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2
Q

Function of pontine micturition centre

A

Co-ordination of bladder and sphincter contraction/relaxation

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3
Q

Function of sacral micturition centre

A

Detrusor contraction

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4
Q

Function of parasympathetic nerves

A

S2-S4 run in pelvic nerve

Detrusor contraction

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5
Q

Function of sympathetic nerves

A
  • T11-L2 run through hypogastric plexus

- detrusor relaxation/sphincter relaxation

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6
Q

Function of somatic nerves

A
  • pudendal nerves arising in Onuf’s nucleus

- sphincter contraction

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7
Q

What happens in the storage phase?

A
  • 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
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8
Q

What happens in the voiding phase?

A
  • 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
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9
Q

What is the bladder function after SCI

A
  • 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
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10
Q

Presentation of Upper Motor Neurone Lesion Bladder Dysfunction

A
  • lesion above SMC
  • bladder reflexes intact
  • loss of conscious control
  • loss of co-ordination
  • detrusor over activity
  • detrusor sphincter dys-synergia
  • autonomic dysreflexia
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11
Q

Lower motor Neurone Lesion Bladder Dysfunction

A
  • lesion below SMC
  • areflexic bladder and sphincters
  • loss of conscious control
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12
Q

How/Why does loss of conscious control present in an UMN lesion?

A
  • no voluntary bladder emptying

- lack of sensation of bladder fullness

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13
Q

Why is detrusor over activity in UMN lesions a problem?

A
  • small capacity bladder
  • reduced compliance
  • incontinence
  • high pressures = danger to upper tracts
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14
Q

Why is DSD in UMN lesions a problem?

A
  • high pressures

- incomplete empyting, infection

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15
Q

How/Why does loss of conscious control present in an LMN lesion?

A
  • no voluntary bladder emptying

- no sensation of bladder fullness

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16
Q

Why is weak sphincters and pelvic floor a problem in LMN lesions?

A
  • incontinence/ stress/ overflow
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17
Q

Why is an areflexic bladder a problem in LMN lesions?

A
  • large capacity bladder
  • chronic retention
  • poor compliance
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18
Q

What does management of the bladder after SCI aim to do?

A
  • reduce pressures = protect upper tracts
  • facilitate emptying
  • improve capacity
  • reduce incontinence
  • improve quality of life
19
Q

What management options are there for the bladder after SCI? What do they do?

A
  • antimuscarinics, Botox injections = reduce pressures
  • SPEC, ICS, urethral stenting, alpha blockers = allows emptying
  • clam ileocystoplasty = improves capacity
  • increase sphincter strength, AUS = reduce incontinence
20
Q

FES for restoring bladder function

A
  • alternative option
  • control bladder by exploiting neuronal circuits
  • current state of the art
21
Q

How does FES work?

A

Exploit neuronal circuits:

  • voiding phase (promotes bladder emptying via neurostimulatiion)
  • storage phase (reduces pressure and increasing capacity via neuromodulation)
22
Q

Sites for FES of the bladder

A
  • bladder wall
  • sacral nerve roots (intra-thecal and extradural)
  • pelvic nerves
  • hypogastric nerves
  • spinal cord stimulation
  • pudendal nerves
  • pelvic floor
  • tibial nerves
23
Q

What is Intra-vesical Electrical Stimulation? How does it work?

A
  • stimulating bladder mechanoreceptor afferents
  • catheter mounted electrode (cathode) placed in urethra
  • anode electrode on abdominal skin over pubic symphysis
24
Q

What has intra-vesical electrical stimulation been used for?

A
  • 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
25
Q

Detrusor muscle stimulation Challenges

A
  • 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
26
Q

Pelvic nerve stimulation challenges

A
  • lower currents required
  • difficult to access nerves
  • concomitant contraction of EUS
27
Q

Finetech Sacral Anterior Root Stimulator (SARSI)

A
  • 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
28
Q

Parts of sacral anterior root stimulator implant (SARSI)

A
  • external control unit
  • external cable
  • transmitter block
  • receiver block
  • implanted cable
  • electrodes
29
Q

Benefits of SARSI with posterior rhizotomy

A
  • complete bladder emptying with low residual
  • posterior rhizotomy
  • increased bowel function
  • implant driven erections
30
Q

Why is complete bladder empyting with low residual an advantage with SARSI + posterior rhizotomy

A
  • reduction in bladder infections

- eliminates need for catheters

31
Q

Why is increased bowel function an advantage with SARSI + posterior rhizotomy

A
  • increases bowel motility, moving stools down colon

- in some patients evacuation occurs by stimulation alone

32
Q

Why is posterior rhizotomy an advantage?

A
  • eliminates reflex incontinece
  • improved bladder compliance
  • reduces autonomic dys-reflexia (associated with bladder)
  • protects from kidney failure
33
Q

Sacral Nerve Neuromodulation

A
  • 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
34
Q

Percutaneous Tibial nerve Stimulation

A
  • 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
35
Q

Spinal cord stimulation

A
  • 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
36
Q

Pudendal nerve stimulation

A
  • 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
37
Q

High Frequency Nerve Blocking

A
  • 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
38
Q

Past, Current and Potential Research at RNOH

A
  • SPARSI and SPAIRS
  • Surface Neuromodulation
  • Wearable devices
  • Pudendal blocking
  • Complete bladder function restoration
39
Q

SPAIRS

A
  • sacral nerve neurostimulation through Finetech SARS
  • no sacral de-afferentation
  • sacral neuromodulation through sacral electrodes
40
Q

What does sacral neuromodulation through sacral electrodes do?

A
  • 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?
41
Q

Optimization of neuromodulation site

A
  • dorsal gential nerve
  • tibial nerve
  • sacral spinal cord
42
Q

CARM

A
  • 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
43
Q

Complete restoration of bladder function

A
  • bladder emptying by stimulation of anterior roots
  • prevention of DSD by pudendal nerve blocking
  • conditional neuromodulation of NDO by pudendal nerve stimulation

Bioengineering in Urology (8 decks)

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