Validation of a data logger for measuring standing time and seat angles for community-based standing devices

Abstract

Context: Little is understood about community-based standing device use and the impact of standing on health outcomes (e.g. pressure injury) in those living with spinal cord injury (SCI). This project reports on the accuracy of a commercially available data logger for measuring standing time and seat angle.

Methods: A standing frame and a standing manual wheelchair were each instrumented with a commercially available data logger and each was tested by an non-disabled participant. Standing time in the standing frame was calculated from the data logger and compared to a user-recorded standing log over a two-month period in a laboratory environment. The standing wheelchair's seat angle was calculated using motion capture and compared to the calculated seat angle from the data logger. Average seat interface pressures were also captured during the testing of the standing wheelchair.

Results: The data logger demonstrated high accuracy (99.99999%) in classifying sitting and standing in the standing frame when compared to a user-recorded standing log. The wheelchair seat angle calculated from the data logger demonstrated a high level of agreement with the motion lab calculations of seat angle (ICC = 0.96 (0.95, 0.97)). The data logger seat angle results also demonstrated strong relationships to average seat pressure and rear dispersion index, measures relevant to pressure injuries.

Conclusions: The data logger appears to be an appropriate tool for determining standing time and seat angle in standing devices, which may aid clinicians and researchers to better understand the use and impact of standing technologies on health outcomes.

Keywords: Accelerometry; Activity trackers; Standing position; Weight-bearing; Wheelchairs.

Figure 1

The two devices tested and placement of data logger on each. A. Standing frame device in seated position. B. Standing frame in standing position set up with approximate location of data logger (blue) and Z-axis (inset). C. Lateral view of the marker set for motion capture calculations, using three makers (blue arrows) on both sides of the manual wheelchair. D. Data logger position along a parallel bar to the seat frame in a multiple-bar linkage system with the Z axis parallel to the seat angle (inset) for manual wheelchair.

Figure 2

The various seat angles of the standing manual wheelchair tested during the motion lab portion of testing with data logger measurements noted in paratheses. A. Full stand (85.1 deg) B. ¾ stand (38.2 deg) C. ½ stand (18.0 deg) D. ¼ stand (5.3 deg) E. Full seated position (−5.8 deg).

Figure 3

Synchronized data signals for seat angle (deg) as measured by the data logger and pressure metrics (average pressure and Dispersion Index [DI]) on the standing wheelchair. Seat angles range from ∼−5 deg (seated) to ∼85 deg (standing) where standing seat angles according to the data logger were approximately 82, 38, 18 and 5 deg respectively.

Figure 4

Down sampled (1 Hz) linear relationship of seat angles as captured by motion capture and data logger with ICC = 0.96.

Figure 5

Down sampled (1 Hz) seat angle (deg) as measured by the data logger vs average pressure (mmHg).

Figure 6

Down sampled (1 Hz) rear cushion Dispersion Index (DI) across seat angles, as measured by the data logger. Vertical red dashed line shows the study cutoff for standing angle (0.5G or 45 deg), and green dashed line shows historical threshold for critical risk for pressure injury from Drummond et al. (15). All data points above our standing angle are below this threshold, reinforcing our choice of thresholds.