Physiology of Micturition

1. Physiology of Micturition Beth Shelly PT, DPT, WCS, BCB PMD www.bethshelly.com

2. Detrusor – smooth mm of the bladder wall Trigone – smooth mm at bladder base Internal sphincter – smooth mm at the bladder neck External sphincter – skeletal mm - PFM

3. Storage Bladder is a reservoir that stores urine (400-600 ml, 13 to 20 oz) Usually fills at a constant rate (slower at night, faster with bladder irritants). Accommodation – detrusor is elastic and allows filling by staying relaxed thus maintaining low bladder pressure The trigone stays closed during filling.

4. Storage First sensation to void - approximately half full (150-200 ml, 5 to 6 ½ oz) sensory stretch receptors in bladder wall give slight perception of need to void – urge Guarding reflex - external sphincter (PFM) stay contracted

5. Storage Postponement of voiding Signals go to sacral micturition center Travels up to the pons Via lateral spinothalamic tract Result - brain inhibits sacral center, bladder keeps filling. Outlet pressure is higher than bladder pressure

6. Emptying At critical level of filling Stretch receptors produce a strong sensation to void – urge Urgency – is sudden compelling desire to void which is difficult to defer (Haylen 2010) Signals go from bladder to brain (pons) Signal returns via somatic track Decision is made to get to the toilet

7. Emptying Position over the toilet Sit or stand Relax overflow muscles – gluteals, adductors, abdominals Maintaining tension in overflow muscles may result in decreased empting External sphincter (PFM) relax → urethral pressure decrease

8. Emptying Internal sphincter/ trigone relaxes Detrusor contracts long and hard enough to empty all but 5 to 50 ml (less than 1 ½ oz) of urine (post void residual). No increase in intra abdominal pressure, one continuous stream Outlet pressure less than bladder pressure

9. Post Void Residual (PVR) • A firm definition of “abnormal” PVR is not universally accepted • Upper limits of normal PVR – 50 (~2 oz) to 100cc (~3 ½ oz) (Haylen 2009) • Abnormal - Most agree that > 200cc (6 ½ oz) is abnormal and consistent with urinary retention • Gray zone - 100 to 200 cc, patient’s diagnosis and other circumstances taken into account to determine correct treatment

10. Post Void Residual (PVR) • PVR percent of total bladder volume (TBV) = PVR/TBV x 100 • Is considered important especially in pediatric patients • PVR of less than 25% of TBV is acceptable (Germain 2003) • 50 ml PVR / 200 ml TBV x 100 = 25%

11. Sensation of Incomplete Empting • ICS definition – complaint that the bladder does not feel empty after micturition (Haylen 2010) • Not a reliable measure • Some feel they are empty when they are not • Some feel the are not empty when they are

12. Sensation of Incomplete Empting • Some feel their bladder must not be empty because they have to urinate again so often • Important for patients to understand • The kidneys make urine continuously • The bladder in never really empty • It is considered normal to have 2 to 3 oz left in the bladder after a normal void

13. Normal Bladder Pattern Total number of voids per 24 hours: 5-7/day (Larsson 1992) Amount of urine voided each time: First morning void - 8 to 12 oz/ void Common daily void – 6 to 8 oz/ void Average time intervals between voiding 2 to 5 hours (young goal 3 - 4 hrs, elderly goal 2 -3 hrs) Total number of nighttime voids 0 to 1/ night under 65ish years old 1 to 2/ night over 65ish years old

14. Autonomic Control of Micturition Sympathetic - Store Parasympathetic – Pee, poop

15. Autonomic Control of Micturition

16. Summary of Voiding Phases

17. Micturition Reflexes Many complex reflexes associated with micturition One reflex allows PFM contraction to results in detrusor relaxation “Stop test” – stop urination Research shows that increased speed of urine interruption = increased PFM strength Not an effective exercise or evaluation tool

18. Practice • PVR means Post void residual • The detrusor is The smooth muscle of the bladder • Urge is the normal gentle sensation of bladder fullness • The abnormal sensation of urge is called Urgency

19. Practice • Total number of voids per 24 hours: • 5-7/day • Amount of urine voided each time: • First morning void - 8 to 12 oz/ void • Common daily void – 6 to 8 oz/ void • Ave time intervals between voiding young • 3 - 4 hrs • Total number of nighttime voids young • 0 to 1/ night under 65ish years old

20. Practice • The correct order of event is 1. Bladder contracts, internal sphincter relaxes, external sphincter relaxes 2. Internal sphincter relaxes, external sphincter relaxes, bladder contracts 3. External sphincter relaxes, internal sphincter relaxes, bladder contracts

21. Practice • Practice explaining normal bladder function to a patient, friend or family member. • Explain normal post void residual and normal bladder patterns • The more you practice the better you will become and the better your patients will understand and be successful at bladder training

22. Keep in Touch Beth Shelly, PT, DPT, WCS, BCB PMD Beth Shelly Physical Therapy Moline, IL 61265 www.bethshelly.com www.pelvicpt.blogspot.com beth@bethshelly.com 563-940-2481