Long-Range Autocorrelations in Parkinson’s Disease as a Reflect of Disease Severity and Dynamic Stability

Warlop, Thibault [UCL] Detrembleur, Christine [UCL] Stoquart, Gaëtan [UCL] Crevecoeur, Frédéric [UCL] Jeanjean, Anne [UCL] Lejeune, Thierry [UCL]

Introduction/Background: Stride duration continuously fluctuates in a complex manner over time, displaying long-range autocorrelations (LRA). The presence of such temporal dynamics is thought to be a critical marker of health and their breakdown as an index of pathological condition, especially associated to dynamic stability in locomotion. However, neurophysiological mechanisms generating such correlations remain a matter of debate. Material and Methods: To further investigate their origin and the influence of pathological locomotion, we studied LRA from 20 parkinsonian patients walking on treadmill and overground at a comfortable speed. The presence of LRA was based on scaling properties of the series variability (Hurst exponent) and the shape of the power spectral density (α exponent). Functional status of each patient was assessed using MDS-UPDRS and modified H&Y scale. Furthermore, to precise the relationship between LRA and the dynamic stability, objective and subjective measures of balance was collected using BESTest and ABC Scale. Spearman’s correlation coefficients were calculated. Results: LRA were highlighted in all patients. However, Hurst and α exponents were significantly higher during treadmill walking (p<0.001). For each exponent, strong correlations were observed on overground walking between H&Y scale and LRA (Hurst: r=-0,831; α: r=- 0,907), and BESTest score and LRA (Hurst: r=0,745; α: r=0,906), while no significant correlations were observed between MDS-UPDRS and ABC Scale with LRA obtained on overground walking. On treadmill, no correlations were observed between functional and balance measures with LRA. Conclusion: This study demonstrates the presence of LRA in parkinsonian gait on overground walking jointly evolving with balance status (BESTest) and supporting the relationship with dynamic stability. Furthermore, the modulation of LRA by treadmill and disease severity (H&Y scale) could suggest further participation of basal ganglia in control mechanisms of LRA.