title: Dynamics of postural control in Parkinson patients with and without symptoms of freezing of gait.
abstract: BACKGROUND
  It has been suggested that dynamical measures such as sample entropy may be more appropriate than conventional measures when analyzing time series data such as postural sway. We evaluated conventional and dynamical measures of postural sway in Parkinson disease (PD) patients with and without freezing episodes.
  
  
  METHODS
  COP (center of pressure) data were recorded during quiet standing with eyes open, eyes closed and while performing a dual task. Data for 16 patients with freezing of gait, 17 patients with no history of freezing and 24 healthy subjects were analyzed. The amount of postural sway was quantified using conventional measures, whereas for the characterization of the temporal structure of the COP data the normalized sway path and sample entropy was calculated.
  
  
  RESULTS
  Mean radius was higher and sample entropy was lower in patients with freezing symptoms as compared to healthy subjects in all three conditions. Dual-tasking significantly increased sway path length in patients with freezing, while normalized sway path did not change over conditions in this group.
  
  
  CONCLUSIONS
  Our findings show that postural sway is characterized by a combination of large radius, short normalized sway path and high regularity of the COP only in patients with freezing. This pattern becomes most prominent in a dual-task paradigm. This may explain higher occurrence of gait freezing in dual task situations with subsequent higher risk of falls. Results suggested that dynamic measures may add valuable information for characterizing postural stability in PD patients.
authors.affiliation: Department of Physical Medicine and Rehabilitation, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany; Department of Neurology, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany. Electronic address: olena.pelykh@med.uni-muenchen.de.
authors.forename: Olena
authors.initials: O
authors.lastname: Pelykh
authors.affiliation: Department of Physical Medicine and Rehabilitation, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany. Electronic address: anke-maria.klein@med.uni-muenchen.de.
authors.forename: Anke-Maria
authors.initials: AM
authors.lastname: Klein
authors.affiliation: Department of Neurology, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany. Electronic address: kai.boetzel@med.uni.muenchen.de.
authors.forename: Kai
authors.initials: K
authors.lastname: Bötzel
authors.affiliation: Department of Neurology, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany. Electronic address: zusanna.kosutzka@med.uni-muenchen.de.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Kosutzka
authors.affiliation: Department of Physical Medicine and Rehabilitation, University Clinics Munich, Marchioninistr. 15, Munich MA 81377, Germany. Electronic address: josef.ilmberger@med.uni-muenchen.de.
authors.forename: Josef
authors.initials: J
authors.lastname: Ilmberger
mesh_terms: D000368:Aged; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*
keywords: Dynamical measures; Freezing; Parkinson patients; Postural control