Pressure ulcer risk detection from complexity of activity

Activity levels in nursing home residents were measured with accelerometers over one week as part of a multicenter randomized controlled trial, and complexity of the resulting activity patterns were characterized. Among 813 study participants on whom activity data had been collected, 16 participants developed pressure ulcers by the end of the study. The fractal dimension D₀ of the activity series was lower (p=0.039) in residents who developed pressure ulcers than in controls matched on the basis of race, randomization group, score on the Braden scale, and diagnoses of cardiovascular disease and dementia. Hurst exponents indicated that the scaling of the power spectrum was close to 1/f in pressure ulcer cases. At timescales exceeding 30 minutes, approximate entropy tended to be higher in the controls than in the pressure ulcer cases. The fractal structure of the activity time series and its information content offer the ability to predict higher risk of development of pressure ulcers in nursing home residents.