Speed and force validation of an improved intravaginal dynamometer design

Abstract

Intravaginal dynamometry can provide reliable and objective assessment of the active and passive properties of the female pelvic floor muscles (PFMs) and associated connective tissues. This work presents a new automated intravaginal dynamometer (IVD) designed to address the limitations of many devices described in the literature, and provides a preliminary mechanical characterization and validation of the system. The new IVD includes dual (anterior and posterior) force measurement probes, minimalistic actuators to reduce IVD size and weight, off-the-shelf components optimized for cost and performance, integrated concurrent electromyography recordings, and an easy-to-use graphic user interface (GUI). IVD load measurements were validated against an Instron® Universal Tester (0-28N) and probe opening speeds were validated using video analysis. A linear regression model was used to quantify the input/output relationship in both cases (α=0.05). While the IVD exhibited -0.828 N bias in load measurements, there was a definitive linear relationship between IVD and Instron® force measurement, with a slope of 0.950 and an excellent model fit (adjR2=1.000). The linear relationships between the GUI set speed of arm opening and true speed measured by video analysis were also excellent (0.958<adjR2<0.991), slopes ranged from 0.874-0.980. The bias and the standard deviation of the bias of speeds ranged from -3.987mm/s to -0.809mm/s and 2.817mm/s to 1.207mm/s, respectively, generally decreasing in magnitude with increasing diameters. While fit was still excellent, speed of opening exhibited lower validity (i.e. lower slopes) at smaller apertures, which may be due to inertia effects. The IVD design presented here demonstrates valid force and speed values during bench testing.