Micturition

Normal Micturition – process of voiding (peeing)

Muscles of bladder – detrusor muscle, urethral smooth muscle, urethral striated muscle (urethral/external sphincter)

Functions of bladder – store and empty urine

filling and storage – accommodation of Ý urine volumes at low intravesical pressure, normal sensation

bladder neck closed both at rest and during Ý intra-abdominal pressure; no uninhibited bladder contractions

emptying – coordinated smooth muscle contraction, relaxation of internal/external sphincters and urethra

bladder actions – voluntary initiation and termination of urination, residual urine<30mL (capacity 400-600 mL), first urge to avoid ~150mL, accommodation, sensation intact, no inhibited contractions

nervous control:

storage

autonomic by efferent sympathetic control (T11-L2 via Hypogastric Nerve) signalling a -receptors in bladder neck and urethra to contract, and b -receptors in bladder body to relax

somatic by efferent fibers from S2-S4 via Pudendal Nerve that innervate external sphincter

emptying

sacral reflex arc – afferent stretch receptors (S2-S4) signal bladder filling to brain; efferent parasympathetic nerves (S2-S4 via Pelvic Nerve)Þ detrusor muscle contraction (and reflexive erections)

injury to nervous system (esp. spinal cord) can disrupt coordinated effort

Urodynamic Evaluation – tests to analyze micturition:

(1) Cystometry – evaluates storage capability of bladder by measuring changes in bladder pressure with Ý bladder volume

normal capacity = 400-750 cc; normal pressure = 6 cm H₂O.

(2) Uroflowmetry – measurement of rate and pattern of flow from bladder, in mL/sec; indicates detrusor and urethra activity

(3) Post void residual profile – negligible in normal bladder

(4) Urethral pressure profile – obtained by recording pressure within urethra down its length

catheter placed in urethra measures resistance; it is slowly withdrawn through the length of the urethra.

(5) Electromyography (EMG) – measures electric potentials from muscle (sphincter, detrusor, and abdominal wall)

useful to demonstrate true detrusor sphincter dyssynergia (discoordinate voiding)

(6) Stop flow test – measures flow and intravesical pressure as a person voluntarily stops urination midstream

ideally done while observing bladder and outlet with fluoroscopy or ultrasonography (videourodynamics)

Urinary Incontinence – defined as failure of voluntary control of urination causing loss of urine via urethra

affects a broad range of patients; often occurs transiently in elderly during changes of environment

Etiology – usually urinary tract diseases or injuries; UTIs, pelvic muscle damage during childbirth, prostate surgery, etc.

Pathology – many potential sources of pathology, often multifactorial

(1) neural injury or disease of brain – low-volume bladder contraction, normal pressure voiding, absence of residual urine, coordination of bladder and sphincter

(2) neural injury or disease of spinal cord above sacral segments – low-volume bladder contraction, high pressure voiding, presence of residual urine, discoordination of bladder and sphincter

(3) injury or disease of bladder (detrusor overactivity or underactivity) – often associated with absent (flaccid), hypotonic, hypertonic, or hyperreflexic (unstable) bladder

(4) obstruction of outlet – can lead to overflow (bladder completely distended and urine trickles out) – common causes:

Obstructive uropathy – residual urine, high bladder pressure, restricted urinary flow

Benign Prostatic Hypertorphy – smooth muscle hyperplasia Þ bladder/urethral obstruction

(5) urethral hypermobility – a.k.a. stress incontinence; leakage with effort or cough; urethra can move into vagina

Diagnosis – from history, including discussion of toileting patterns; physical examination

check list of medications to see if they are affecting bladder/sphincter
urodynamic evaluation – confirms diagnosis, suggests effective therapy, estimates prognosis

Treatment – medication, surgery, artificial urinary sphincter, contigen implant