title: Does vaginal closure force differ in the supine and standing positions?
abstract: OBJECTIVE
  This study was undertaken to quantify resting vaginal closure force (VCF(REST)), maximum vaginal closure force (VCF(MAX)), and augmentation of vaginal closure force augmentation (VCF(AUG)) when supine and standing and to determine whether the change in intra-abdominal pressure associated with change in posture accounts for differences in VCF.
  
  
  METHODS
  Thirty-nine asymptomatic, continent women were recruited to determine, when supine and standing, the vaginal closure force (eg, the force closing the vagina in the mid-sagittal plane) and bladder pressures at rest and at maximal voluntary contraction. VCF was measured with an instrumented vaginal speculum and bladder pressure was determined with a microtip catheter. VCF(REST) was the resting pelvic floor tone, and VCF(MAX) was the peak pelvic floor force during a maximal voluntary contraction. VCF(AUG) was the difference between VCF(MAX) and VCF(REST). T tests and Pearson correlation coefficients were used for analysis.
  
  
  RESULTS
  VCF(REST) when supine was 3.6 +/- 0.8 N and when standing was 6.9 +/- 1.5 N--a 92% difference (P < .001). The VCF(MAX) when supine was 7.5 +/- 2.9 N and when standing was 10.1 +/- 2.4 N--a 35% difference (P < .001). Bladder pressure when supine (10.5 +/- 4.7 cm H2O) was significantly less (P < .001) than when standing (31.0 +/- 6.4 cm H2O). The differences in bladder pressure when either supine or standing did not correlate with the corresponding differences in VCF at rest or at maximal voluntary contraction. The supine VCF(AUG) of 3.9 +/- 2.7 N, was significantly greater than the standing VCF(AUG) of 3.3+/-1.9 N.
  
  
  CONCLUSIONS
  With change in posture, vaginal closure force increases because of higher intra-abdominal pressure and greater resistance in the pelvic floor muscles.
authors.affiliation: Department of Obstetrics and Gynecology, Pelvic Floor Research Group, University of Michigan Medical School, Ann Arbor 48109, USA. morgand@umich.edu
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Morgan
authors.forename: Gurpreet
authors.initials: G
authors.lastname: Kaur
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Hsu
authors.forename: Dee E
authors.initials: DE
authors.lastname: Fenner
authors.forename: Kenneth
authors.initials: K
authors.lastname: Guire
authors.forename: Janis
authors.initials: J
authors.lastname: Miller
authors.forename: James A
authors.initials: JA
authors.lastname: Ashton-Miller
authors.forename: John O L
authors.initials: JO
authors.lastname: Delancey
mesh_terms: D000328:Adult; D004867:Equipment Design; D005260:Female; D006176:Gynecology / Q000295:instrumentation; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D017773:Pelvic Floor / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012016:Reference Values; D012146:Rest; D016683:Supine Position; D013525:Surgical Instruments; D001743:Urinary Bladder / Q000502:physiology; D014621:Vagina / Q000502:physiology*