Abstract
Background The Instrumented Stand and Walk (ISAW) test, which includes 30 seconds of stance, step initiation, gait, and turning, results in many objective balance and gait metrics from body-worn inertial sensors. However, it is not clear which metrics provide independent information about mobility.
Objective It was hypothesized that balance and gait represent several independent domains of mobility and that not all domains would be abnormal in individuals with Parkinson disease (PD) or would change with levodopa therapy.
Design This was a cross-sectional study.
Methods A factor analysis approach was used to identify independent measures of mobility extracted from the ISAW in 100 participants with PD and 21 control participants. First, a covariance analysis showed that postural sway measures were independent of gait measures. Then, the factor analysis revealed 6 independent factors (mobility domains: sway area, sway frequency, arm swing asymmetry, trunk motion during gait, gait speed, and cadence) that accounted for 87% of the variance of performance across participants.
Results Sway area, gait speed, and trunk motion differed between the PD group in the off-levodopa state and the control group, but sway frequency (but not sway area) differed between the PD group in the off-levodopa state and the control group. Four of the 6 factors changed significantly with levodopa (off to on): sway area, sway frequency, trunk motion during gait, and cadence. When participants were on levodopa, the sway area increased compared with off levodopa, becoming more abnormal, whereas the other 3 significant metrics moved toward, but did not reach, the healthy control values.
Limitations Exploratory factor analysis was limited to the PD population.
Conclusions The different sensitivity various balance and gait domains to PD and to levodopa also support neural control of at least 6 independent mobility domains, each of which warrants clinical assessment for impairments in mobility.
Footnotes
All authors provided concept/idea/research design. Dr Horak, Dr Mancini, Dr Carlson-Kuhta, and Dr Salarian provided writing. Dr Horak, Dr Carlson-Kuhta, and Dr Salarian provided data collection. Dr Mancini and Dr Salarian provided data analysis. Dr Horak and Dr Carlson-Kuhta provided project management. Dr Horak provided fund procurement, facilities/equipment, and institutional liaisons. Dr Nutt provided participants. Dr Horak, Dr Nutt, and Dr Salarian provided consultation (including review of manuscript before submission).
This study was approved by the Institutional Review Board of Oregon Health & Science University.
This publication was made possible with support from a grant from the National Institute on Aging (AG006457); a Challenge Grant from the National Institute of Neurological Disorders and Stroke (RC1 NS068678) and from the Oregon Clinical and Translational Research Institute at Oregon Health & Science University; and grant number UL1 RR024140 from the National Center for Research Resources, a component of the National Institutes of Health (NIH), and the NIH Roadmap for Medical Research.
Oregon Health & Science University and Dr Horak have a significant financial interest in APDM, a company that may have a commercial interest in the results of this research and technology. This potential institutional and individual conflict has been reviewed and managed by OHSU.
- Received October 17, 2015.
- Accepted March 28, 2016.
- © 2016 American Physical Therapy Association
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