Instrumented Modified Clinical Test of Sensory Interaction on Balance

The original CTSIB is a clinical version of the SOT.^{18 (link),19 (link)} It uses a stop-watch to measure duration of independent standing under 6 sensory conditions, substituting a compliance foam surface for the sway-referenced surface and a visual conflict doam for the sway referenced visual surround.^{18 (link)} As previously reported,^{19 (link),20 (link)} the CTSIB has good test-retest reliability in community-dwelling older adults. Using SOT as the criterion measure, the CTSIB has also been reported to correlate moderately with 90% sensitivity and 95% specificity.^{19 (link)} The CTSIB was later modified to eliminate the visual conflict doam and includes 4 increasingly challenging balance conditions: C1 = firm surface eyes open, C2 = firm surface eyes closed, C4= eyes open foam surface, and C5 eyes closed foam surface. Participants stand upright with feet together and arms across the chest for 30 seconds, first on a firm surface with and without vision, then on an Airex, medium density foam pad (18 in × 18 in × 5 in) with and without vision.^{18 (link)} Each condition is scored on an ordinal scale based on performance in time and sway 0–3 (0= unable, 1=˂30s, 2=30s unstable, 3=30s stable). To instrument the mCTSIB, 1 wireless tri-axial body-worn inertial sensor (Opal by APDM, Inc) was placed at L-5 with an elastic belt (Figure 1b). The system included a set of Opals with a docking station and an access point for wireless data transmission, from which the anterior-posterior (AP) and medio-lateral (ML) directions of change were used to quantify postural sway after wirelessly transmitted to a laptop using Mobility Lab software from APDM (Figure 1a). Postural sway metrics, were quantified during each stance condition.^{13 (link)} Although the system automatically calculates amplitude, velocity, frequency and jerkiness of postural sway in the ML direction, AP direction as well as an average of both directions, we used the amplitude measure in the AP direction (range) as the primary metric since it is equivalent to the peak-to-peak measure used to calculate the SOT equilibrium score by NeuroCom. This AP range measure, which has equal intervals and an absolute zero, is defined as the range of acceleration [m] ([m/s2]).^{12 (link)} In PD, the Opal range measure has been shown to be more responsive than clinical measures^{13 (link),21 (link)} and have good test-retest reliability (ICC of 0.82) and significantly correlate with the clinical postural stability score r = 0.56.^{12 (link)}