Assessing postural control and postural control strategy in diabetes patients using innovative and wearable technology

Abstract

Introduction: Currently, diagnosis of patients with postural instability relies on a rudimentary clinical examination. This article suggests an innovative, portable, and cost-effective prototype to evaluate balance control objectively.

Methods: The proposed system uses low-cost, microelectromechanical sensor, body-worn sensors (BalanSens) to measure the motion of ankle and hip joints in three dimensions. We also integrated resulting data into a two-link biomechanical model of the human body for estimating the two-dimensional sway of the center of mass (COM) in anterior-posterior (AP) and medial-lateral (ML) directions. A new reciprocal compensatory index (RCI) was defined to quantify postural compensatory strategy (PCS) performance. To validate the accuracy of our algorithms in assessing balance, we investigated the two-dimensional sway of COM and RCI in 21 healthy subjects and 17 patients with diabetic peripheral neuropathic (DPN) complications using the system just explained. Two different conditions were examined: eyes open (EO) and eyes closed (EC) for duration of at least 30 seconds. Results were compared with center of pressure sway (COP) as measured by a pressure platform (Emed-x system, Novel Inc., Germany). To further investigate the contribution of the somatosensory (SOM) feedback to balance control, healthy subjects performed EO and EC trials while standing on both a rigid and a foam surface.

Results: A relatively high correlation was observed between COM measured using BalanSens and COP measured using the pressure platform (r = 0.92). Results demonstrated that DPN patients exhibit significantly greater COM sway than healthy subjects for both EO and EC conditions (p < 0.005). The difference becomes highly pronounced while eyes are closed (197 +/- 44 cm(2) vs 68 +/- 56 cm(2)). Furthermore, results showed that PCS assessed using RCI is significantly better in healthy subjects compared to DPN subjects for both EO and EC conditions, as well as in both ML and AP directions (p < 0.05). Alteration in SOM feedback in healthy subjects resulted in diminished RCI values that were similar to those seen in DPN subjects (p > 0.05).

Discussion/conclusion: This study suggested an innovative system that enables the investigation of COM as well as postural control compensatory strategy in humans. Results suggest that neuropathy significantly impacts PCS.

2010 Diabetes Technology Society.

Figures

Figure 1.

BalanSens™ system: (A) two sensor units allow providing three-dimensional angles of ankle and hip joints. A central unit allows transferring the estimated angles in real time to a computer via a WiFi communication protocol. A researchable battery allows recording and transferring data unto a 2-hour continuous measurement. If necessary, the battery can be replaced easily. (B) Representation of the axes angles.

Figure 2.

Two-link biomechanical model of human body for estimating COM trajectory.

Figure 3.

Experimental setup: two sensors were attached, one to subject’s lower back and one to the shin. These sensors allow measuring three-dimensional angles of ankle and hip joints. Software was developed to estimate the trajectory of COM, ankle, and hip in real time using a two-link biomechanical model of a human body. Balance control and postural compensatory strategy of subjects were assessed during eyes-open and eyes-closed conditions while standing on a hard surface or a soft surface (using a firm and thick foam). A pressure platform was used as the gold standard to examine accuracy of the system to screen balance deterioration due to sensory alteration.

Figure 4.

The area of sway for COP was measured using a standard pressure platform. Only the area of sway during a double stance condition was calculated, and COP values related to a single stance condition were excluded in the analysis.

Figure 5.

To examine the impact of SOM feedback alteration on balance control, subjects were asked to stand on a firm and thick foam.

Figure 6.

An excellent agreement was observed between COM estimated using BalanSens and COP measured using the gold standard.

Figure 7.

The area of sway for (A) COM, (B) hip joint, and (C) ankle joint for healthy subjects while standing on a hard surface (healthy SOM feedback), DPN subjects (distorted SOM feedback), and healthy subjects while standing on a soft surface (distorted SOM feedback).

Figure 8.

Postural compensatory strategy quantified by RCI value in (A) anterior–posterior (AP)direction and (B) medial–lateral (ML)directions.