Physiology of micturition

Question 1

What is a safe bladder?

Answer 1

low pressure storage vessel

Question 2

What happens if the bladder is high pressure?

Answer 2

hydronephrosis
renal impairment
incontinence

Question 3

What happens to the detrusor and sphincters of the bladder during voiding?

Answer 3

smooth muscle of internal urethral sphincter relaxed
striated muscle of external sphincter relaxed
detrusor muscle contracts

Question 4

What can go wrong with the detrusor muscle if the neurology is disrupted?

Answer 4

detrusor contracts too much:
- failure of detrusor to store at low pressure
- leakage, high pressure transmitted to upper tracts

detrusor muscle doesn’t contract enough:
- failure of detrusor to contract during emptying
- incomplete emptying, urinary retention
- LUTS, UTIs, high pressure retention

Question 5

What can go wrong with the urethral sphincter mechanism if the neurology is disrupted?

Answer 5

doesn’t contract enough:
- failure/inadequate contraction during storage phase
- leakage - stress incontinence

sphincter doesn’t relax:
- detrusor contracts against closed sphincter
- detrusor-sphincter dyssynergia
- incomplete emptying + high pressure transmitted to upper tracts

Question 6

How is bladder physiology tested?

Answer 6

urodynamics

Question 7

How is detrusor pressure calculated from urodynamics?

Answer 7

rectum pressure - bladder pressure when a patient coughs

Question 8

What is autonomic dysreflexia?

Answer 8

occurs in high spinal cord lesions (eg. C spine lesions)
stimulation of spinal cord below level of injury (eg. blocked catheter, UTI) leads to sympathetic overactivity
patients will carry GTN spray or sublingual Ca2+ channel blocker

Question 9

What happens to the bladder in MS?

Answer 9

detrusor overactivity
poor bladder emptying
safe bladder
no need for urodynamics at initial assessment
most end up on medication and self-catheterisation

Question 10

How can low pressure bladder storage be improved?

Answer 10

antimuscarinics - reduction of detrusor pressure, treats urgency and urge incontinence
eg. oxybutynin, solifenacin

Question 11

Why are suprapubic catheters preferable to urethral catheters in patients with spinal cord injuries?

Answer 11

patients often have poor sensation
cannot feel urethral catheter being pulled/can cause damage to urethra