Design and validation of an automated dual-arm instrumented intravaginal dynamometer

(1) To present the design of a novel intravaginal dynamometer (IVD) capable of measuring vaginal closure force on both the anterior and posterior arms, (2) to use bench testing to validate the force, speed of arm opening, and positional accuracy of load measurement along the IVD arms, and (3) to present in vivo force measurements made with this device, comparing forces measured by the anterior and posterior arms.

IVD load measurements were validated against an Instron® Universal Tester, arm opening speeds were validated using video analysis, and position-load accuracy was validated against calibration weights. In vivo IVD data were acquired from female volunteers during passive opening and pelvic floor muscle contraction tasks. Anterior and posterior IVD arm force outcomes were compared.

Forces measured by the IVD and Instron® exhibited a strong linear relationship with excellent model fit. The speed control system was valid when tested under physiological loading conditions, however smaller antero-posterior opening diameters (25 and 30 mm) exhibited some error. The loading position along the IVD arms had no effect on force outcomes. In vivo data exhibited differences between force outcomes measured at the anterior and posterior aspects of the vagina during active contraction and passive elongation of the pelvic floor muscles.

This IVD design demonstrates valid load measurement and speed control during bench testing. Active and passive forces measured are consistent with the literature. With dual instrumented arms, this device allows for further investigation into the source of measured vaginal closure forces.