Dynamic sitting to prevent pressure ulcers in spinal cord injured

At present, clinical interventions and research efforts are not fully successful in defining the risk of pressure ulcer development and as such in eventually preventing pressure ulcers. As a result, the prevalence and incidence values of pressure ulcers remain unacceptably high. It is common sense that healthy subjects do not develop pressure ulcers due to a dynamic variation in sitting posture. This dynamic sitting behavior can be identified and used as a reference values for the optimal sitting behavior of individuals that use a wheelchair and are at risk of developing pressure ulcer. The main research question that has been answered in this thesis is if imposing dynamic sitting behavior by means of the Dynasit chair in Spinal Cord Injured individuals results in elevated tissue viability? \ud In order to define a reference values for the sitting behavior of spinal cord injured individuals, an analysis of healthy sitting behavior has been performed. It was found that healthy subjects change their sitting posture at least every eight minutes. To impose this dynamic sitting behavior on spinal cord injured individuals, the Dynasit chair has been developed. The Dynasit chair is an experimental sitting device developed to investigate the effects of different sitting postures, alternating tuberal support and pelvic orientations on the (sub-) cutaneous tissue viability. Two studies on healthy subjects demonstrated the positive effect of actuation with the Dynasit chair on the tissue load. Regarding the main research question of this thesis, a study performed in 10 male spinal cord injured individuals, confirmed the ability of the Dynasit chair to impose dynamic sitting behavior, based on healthy sitting behavior, in spinal cord injured individuals. This imposed dynamic sitting behavior resulted in significant elevation of the (sub-) cutaneous tissue oxygenation. This elevated tissue oxygenation implies that due to the dynamic sitting, the wheelchair user can sit for prolonged periods of time without tissue breakdown

Analysis of healthy sitting behavior: Interface pressure distribution and subcutaneous tissue oxygenation

Pressure ulcers are a large problem in individuals who use a wheelchair for their mobility and have limited trunk stability and motor function. Because no relation between interface pressure and pressure ulcer development has been established and no clinical threshold for pressure ulcer development can be given, looking at the sitting behavior of nondisabled individuals is important. Nondisabled individuals do not develop pressure ulcers because they continuously shift posture. We analyzed the sitting behavior of 25 nondisabled male subjects by using a combination of interface pressure measurement and subcutaneous tissue oxygenation measurement by means of the Oxygen to See. These subjects shifted posture on average 7.8 +/- 5.2 times an hour. These posture shifts were merely a combination of posture shifts in the frontal and sagittal plane. Subcutaneous oxygen saturation increased on average 2.2% with each posture adjustment, indicating a positive effect of posture shifts on tissue viability. The results of this study can be used as a reference for seating interventions aimed at preventing pressure ulcers. Changing the sitting load at least every 8 minutes is recommended for wheelchair users

Estimating qualitative parameters for assessment of body balance and arm function in a simulated ambulatory setting

Continuous daily-life monitoring of balance control and arm function of stroke survivors in an ambulatory setting, is essential for optimal guidance of rehabilitation. In a simulated ambulatory setting, balance and arm function of seven stroke subjects is evaluated using on-body measurement systems (Xsens MVN Biomech and the Xsens Instrumented Force Shoes). Ethical approval for this study was obtained. Qualitative parameters of body balance and arm function are estimated and compared with the results of a generally accepted clinical balance assessments (e.g. Berg Balance Scale and Fugl-Meyer)

Quantifying and correcting for speed and stride frequency effects on running mechanics in fatiguing outdoor running

Measuring impact-related quantities in running is of interest to improve the running technique. Many quantities are typically measured in a controlled laboratory setting, even though most runners run in uncontrolled outdoor environments. While monitoring running mechanics in an uncontrolled environment, a decrease in speed or stride frequency can mask fatigue-related changes in running mechanics. Hence, this study aimed to quantify and correct the subject-specific effects of running speed and stride frequency on changes in impact-related running mechanics during a fatiguing outdoor run. Seven runners ran a competitive marathon while peak tibial acceleration and knee angles were measured with inertial measurement units. Running speed was measured through sports watches. Median values over segments of 25 strides throughout the marathon were computed and used to create subject-specific multiple linear regression models. These models predicted peak tibial acceleration, knee angles at initial contact, and maximum stance phase knee flexion based on running speed and stride frequency. Data were corrected for individual speed and stride frequency effects during the marathon. The speed and stride frequency corrected and uncorrected data were divided into ten stages to investigate the effect of marathon stage on mechanical quantities. This study showed that running speed and stride frequency explained, on average, 20%–30% of the variance in peak tibial acceleration, knee angles at initial contact, and maximum stance phase knee angles while running in an uncontrolled setting. Regression coefficients for speed and stride frequency varied strongly between subjects. Speed and stride frequency corrected peak tibial acceleration, and maximum stance phase knee flexion increased throughout the marathon. At the same time, uncorrected maximum stance phase knee angles showed no significant differences between marathon stages due to a decrease in running speed. Hence, subject-specific effects of changes in speed and stride frequency influence the interpretation of running mechanics and are relevant when monitoring, or comparing the gait pattern between runs in uncontrolled environments