Detrended fluctuation analysis of temporal variation of the center of pressure (COP) during quiet standing in parkinsonian patients

Abstract

[Purpose] Parkinson's disease (PD) leads to stance instability in the late stage of the disease. Conventional studies of the center of pressure (COP) have difficulties characterizing postural instability in the early stage of PD. The present study analyzed stabilograms of PD patients using a recently developed method, detrended fluctuation analysis (DFA). [Subjects] The subjects were 7 PD patients in stages I-III of Hoehn and Yahr, and 10 age-matched healthy elderly (HE) persons. [Method] COP signals were measured during quiet standing, and subjected to DFA and conventional analysis. DFA parameters (scaling exponents) relating COP fluctuation to time interval showed similar behaviors both in PD and HE subjects. Both in the anterior-posterior (AP) and medio-lateral (ML) directions, three exponents, α1, α2 and α were obtained for short-and long-term fluctuations, and the whole range, respectively. [Results] Magnitudes α, α1 and α2 were almost the same: α1 ≈1.5, α2 ≈1.0, and α ≈1.3. The crossover points dividing the shortand long-term fluctuations in the AP direction, however, differed between PD and HE subjects. The former was about 0.6 times shorter than the latter. [Conclusion] PD patients may control upright posture with the similar postural strategies to HE subjects, but the switching times between the short-and long-term strategies may be different.