title: Validity and reliability of an instrumented speculum designed to minimize the effect of intra-abdominal pressure on the measurement of pelvic floor muscle strength.
abstract: BACKGROUND
  Measurements of pelvic floor muscle strength are contaminated by crosstalk from intra-abdominal pressure. We tested an improved instrumented speculum designed to minimize this crosstalk. The hypotheses were that the speculum yields: 1) maximum vaginal closure forces unrelated to intra-abdominal pressure, 2) discriminatory validity between women with strong vs. weak pelvic floor muscles, and 3) acceptable test-retest reliability.
  
  
  METHODS
  Maximum voluntary vaginal closure force was measured in 40 incontinent women (20-77 years) on two visits spaced one month apart. At the baseline visit, intra-abdominal pressure was also estimated via intra-vesical catheterization during the vaginal closure force measurement. Subjective estimate of pelvic floor muscle strength was also assessed using digital palpation by a skilled examiner to determine group placement as "strong" (n=31) or "weak" (n=9).
  
  
  RESULTS
  Vaginal closure force was not significantly correlated with intra-abdominal pressure (r=-.26, P=.109). The groups with subjectively scored strong and weak pelvic floor muscles differed significantly by mean [SD] maximum vaginal closure force (3.8 [1.7] vs. 1.9 [0.8] N respectively, P<.01.) Across both time points the mean vaginal closure force was 3.42 [1.67] N with a range of .68 to 9.05 N. Mean Visit 1 and Visit 2 vaginal closure force scores did not differ (3.41 [1.8] and 3.42 [1.6] N, respectively). The vaginal closure force repeatability coefficient was 3.1N.
  
  
  CONCLUSIONS
  The improved speculum measured maximum vaginal closure force without evidence of crosstalk from intra-abdominal pressure, while retaining acceptable discriminant validity and repeatability.
authors.affiliation: Department of Mechanical Engineering, University of Michigan College of Engineering, Ann Arbor, MI, United States. Electronic address: jaam@med.umich.edu.
authors.forename: James A
authors.initials: JA
authors.lastname: Ashton-Miller
authors.affiliation: University of Michigan School of Nursing, Ann Arbor, MI, United States.
authors.forename: Ruth
authors.initials: R
authors.lastname: Zielinski
authors.affiliation: Department of Obstetrics & Gynecology, University of Michigan Medical School, Ann Arbor, MI, United States.
authors.forename: John O L
authors.initials: JO
authors.lastname: DeLancey
authors.forename: Janis M
authors.initials: JM
authors.lastname: Miller
mesh_terms: D000328:Adult; D000368:Aged; D004867:Equipment Design; D005260:Female; D006801:Humans; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D017773:Pelvic Floor / Q000502:physiology*; D015203:Reproducibility of Results; D013525:Surgical Instruments; D014621:Vagina / Q000502:physiology*; D055815:Young Adult
keywords: Instrumented speculum; Levator ani; Repeatability; Strength; Vaginal closure force