Correlation of ISO 16840-2:2007 impact damping and hysteresis measures for a sample of wheelchair seating cushions.

Hysteresis and impact damping measures were made on 37 wheelchair seating cushions according to ISO 16840-2:2007 Wheelchair seating-Part 2: Determination of physical and mechanical characteristics of devices intended to manage tissue integrity-seat cushions. These measures were then correlated using Spearman and Pearson correlations to investigate the relationship between them. Correlations were also conducted on the subset of cushions comprising only those with planar foam construction. Correlation between the hysteresis measures (h250 and h500) and the mean number of rebounds greater in amplitude than 10% of the peak acceleration amplitude (R10%) were weak, as were the correlations between the hysteresis measures and the mean peak first rebound acceleration (aa). Correlations between hysteresis and the mean peak second rebound acceleration (a2), and also hysteresis and the ratio of first and second peak (a2:aa) however were moderate. Results demonstrate that the relationship between these two measures is complex. The assertion implicit in ISO 16840-2:2007 is that the two measures are related, but this study shows that these should not be assumed to be equivalent or used interchangeably.

A quantitative measurement method for comparison of seated postures.

This technical note proposes a method to measure and compare seated postures. The three-dimensional locations of palpable anatomical landmarks corresponding to the anterior superior iliac spines, clavicular notch, head, shoulders and knees are measured in terms of x, y and z co-ordinates in the reference system of the measuring apparatus. These co-ordinates are then transformed onto a body-based axis system which allows comparison within-subject. The method was tested on eleven unimpaired adult participants and the resulting data used to calculate a Least Significant Difference (LSD) for the measure, which is used to determine whether two postures are significantly different from one another. The method was found to be sensitive to the four following standardised static postural perturbations: posterior pelvic tilt, pelvic obliquity, pelvic rotation, and abduction of the thighs. The resulting data could be used as an outcome measure for the postural alignment aspect of seating interventions in wheelchairs.

ISO 16840-2:2007 load deflection and hysteresis measurements for a sample of wheelchair seating cushions.

Load deflection and hysteresis measurements were made on 37 wheelchair seating cushions according to ISO 16840-2:2007. Load deflection plots for all 37 cushions are reported and fundamental aspects of graph interpretation discussed. ISO hysteresis data are also reported and interpretation discussed.

Can static interface pressure mapping be used to rank pressure-redistributing cushions for active wheelchair users?

Interface pressure mapping (IPM) is a clinical tool that assists the selection of seat cushions for pressure management for wheelchair users. Clinical pressure measurements are almost always made under static sitting conditions, although this does not consider the time-dependent properties of some cushion materials that may behave differently under the dynamic conditions of self-propulsion. This study investigated the potential for such differences by collecting seat IPM measurements from eight wheelchair users using four different seat cushion designs during static sitting and self-propulsion. Mean pressure corresponding to the approximate anatomical location of the ischial tuberosities was used to rank the four cushions under the two conditions. The two sets of rankings for each participant were then compared using correlation. Dynamic data from four participants was judged too inconsistent to be interpreted reliably and demonstrates the practical difficulties associated with dynamic IPM measurement when variations in individual propulsion technique cannot be controlled. Strong correlations were observed between rank orders for the remaining four participants and suggest that the statically derived pressure measures can be used for clinical decision making when selecting cushions for self-propelling wheelchair users.