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abstract

401 - AN AUTOMATED, SERVO-CONTROLLED INTRAVAGINAL DYNAMOMETER TO ASSESS MECHANICAL TISSUE PROPERTIES OF THE PFMS IN WOMEN: IMPORTANT FACTORS TO CONSIDER WHEN DEVELOPING A CLINICAL OR EXPERIMENTAL PROTOCOL

401

AN AUTOMATED, SERVO-CONTROLLEDINTRAVAGINAL DYNAMOMETER TO ASSESS MECHANICAL TISSUE PROPERTIES OFTHE PFMS IN WOMEN: IMPORTANT FACTORS TO CONSIDER WHEN DEVELOPING ACLINICAL OR EXPERIMENTAL PROTOCOL

M. BERUBE, C. S. CZYRNYJ, L. B.MCLEAN;
Univ. of Ottawa, Ottawa, Canada.

Introduction: Intravaginaldynamometry is used to measure pelvic floor muscle (PFM) strength andpassive tissue properties [1,2]. We have developed an automatedintravaginal dynamometer that allows customization of aperture,speeds of aperture opening, and hold time.
Objective: (1)To investigate the reliability of PFM maximum voluntary contraction(MVC) force and passive intravaginal tissue resistance recorded usingthe dynamometer. (2) To compare forces recorded during PFM MVCs attwo apertures and passive intravaginal resistance recorded at twovelocities of aperture opening.
Methods: The protocol wasapproved by our institutional research ethics board. Nulliparouswomen provided written informed consent, and attended afamiliarization session (V1) and two dynamometry sessions (V2, V3) atone week intervals. In supine with the dynamometer inserted into thevagina, the arms were opened to 25mm diameter and, once the baselinewas stable, women held a 5s MVC of their PFMs. The task was repeatedusing a 35mm diameter. Next, to assess resistance to passive stretch,the arms of the dynamometer were opened, at a constant velocity(18mm/s or 9mm/s), from an initial diameter of 15mm to 40mm and heldat this aperture for 5s. Three trials of each task were performed,with 90s of rest between trials. Force data, sampled at 100Hz, werefiltered using a 4th order, low pass (5Hz) Butterworth filter.Outcomes included baseline force, peak force, relative peak force andmaximal rate of force development, (Figure 1). Trials with evidenceof reflex PFM activation were removed from the analysis. ANOVAs wereused to test for trial and day effects and for differences betweenapertures and opening speeds (α=0.05). Intra-class correlationcoefficients (ICCs), and minimal detectable change (MDC) werecomputed.
Results: Twenty nulliparous women [age= 35(±15)years; body mass index= 23(±4) kg/m2] participated. Therewere no between trial effects for MVC outcomes, but most resistanceto passive stretch outcomes were higher for trial 1 than for trials 2and 3, thus ICC and MDC were computed using trials 2 and 3 only.Between-trial reliability was very good to excellent (Tables 1 &2). No significant between day effects were found for any outcomes.Between-day reliability of baseline resistance and peak force wasvariable, yet the reliability of relative peak force was very good.Baseline force, peak force, relative peak force, and rate of forcedevelopment were all higher with the larger aperture. Relative peakforce (V2 only) and rate of force development were higher using fastcompared to the slow aperture opening.


Figure 1. (A)Custom intravaginal dynamometer. (B) Sample data recorded during amaximal voluntary pelvic floor muscle contraction (diameter = 35 mm).(C) Sample data recorded during a passive stretch (aperture openingat 18mm/s).

Maximumvoluntary contraction (MVC) outcomes. *=significant differencebetween diameters.


Mean(±SE)

ICC(95% CI)

MDC

V2

V3

V2

V3

V2-V3

V2-V3

MVCat 25 mm

Baseline(N)

6.98± 0.38*

7.46± 0.45*

0.95(0.89-0.98)

0.94(0.87-0.97)

0.52(-0.27-0.82)

3.36

PeakForce (N)

12.39± 0.42*

13.03± 0.51*

0.95(0.89-0.98)

0.96(0.92-0.98)

0.11(-1.37-0.67)

5.08

Rateof Force Development (N/s)

17.44± 1.66*

18.03± 2.35*

0.91(0.80-0.96)

0.90(0.80-0.96)

0.89(0.69-0.96)

7.51

RelativePeak Force (N)

5.41± 0.32*

5.51± 0.48*

0.91(0.82-0.96)

0.95(0.89-0.98)

0.82(0.51-0.93)

2.03

MVCat 35mm

Baseline(N)

11.00± 0.51*

11.25± 0.69*

0.90(0.80-0.96)

0.93(0.84-0.97)

0.85(0.59-0.95)

2.62

PeakForce (N)

20.39± 0.71*

20.77± 0.75*

0.94(0.87-0.98)

0.94(0.87-0.98)

0.75(0.30-0.91)

4.13

Rateof Force Development (N/s)

28.56± 3.24*

27.08± 3.66*

0.89(0.77-0.96)

0.92(0.81-0.97)

0.93(0.79-0.97)

10.16

RelativePeak Force (N)

9.32± 0.62*

9.54± 0.79*

0.94(0.86-0.98)

0.95(0.90-0.98)

0.87(0.64-0.95)

2.87


Passiveresistance outcomes. *=significant difference between speeds.


Mean(±SE)

ICC(95% CI)

MDC

V2

V3

V2

V3

V2-V3

V2-V3

Resistanceat 40mm - 9mm/s

Baseline(N)

3.39± 0.39

3.27± 0.25

0.91(0.76-0.97)

0.89(0.73-0.96)

0.72(0.21-0.90)

1.77

PeakForce (N)

15.67± 1.05

15.52± 0.81

0.98(0.94-0.99)

0.96(0.90-0.99)

0.64(0.04-0.87)

5.85

Rateof Force Development (N/s)

19.39± 0.75*

19.31± 0.84*

0.82(0.57-0.93)

0.94(0.84-0.98)

0.75(0.35-0.90)

4.95

RelativePeak Force (N)

11.30± 0.65*

12.22± 0.71

0.91(0.77-0.97)

0.96(0.89-0.98)

0.71(0.21-0.89)

4.02

Resistanceat 40mm - 18mm/s

Baseline(N)

3.56± 0.20

3.41± 0.22

0.89(0.74-0.96)

0.91(0.78-0.97)

0.25(-1.01-0.72)

2.41

PeakForce (N)

17.75± 1.03

17.64± 0.83

0.96(0.89-0.98)

0.95(0.87-0.98)

0.85(0.61-0.95)

4.16

Rateof Force Development (N/s)

36.89± 1.58*

36.99± 1.52*

0.83(0.62-0.93)

0.95(0.88-0.98)

0.76(0.40-0.91)

10.32

RelativePeak Force (N)

14.35± 0.94*

14.00± 0.77

0.96(0.90-0.99)

0.96(0.89-0.98)

0.80(0.47-0.92)

4.51


Conclusions: Ourservo-controlled dynamometer yields very good to excellentbetween-trial reliability and moderate to very good between-dayreliability. Maximum force generating capacity of the PFMs is morereliable using relative compared to absolute forces. When setting aprotocol and/or comparing studies, aperture and rate of apertureopening should be carefully controlled, as these parameterssignificantly impact outcomes.
References: 1. Neurourol.Urodyn., vol. 22, no. 7, pp. 648-653, 2003 2. Neurourol Urodyn.,vol.32, no. 6, pp.658-659, 2013