Postural responses to balance perturbations in individuals with Supratentorial Stroke and Idiopathic Parkinson's Disease

Falls are a major health problem in our aging population. Since balance
deficits are the most important risk factor for falls, it is not surprising
that in the population of Parkinson (PD) and stroke patients, in whom balance
deficits are very common, the problem of falls is paramount. We have planned a
prospective cohort study using a new experimental setup (Radboud Falls
Simulator) where we intend to predict falls and to better understand the
mechanisms of postural instability in PD and stroke patients. For both groups,
some questions remain to be answered to improve the interpretation of the
results of cohort study. These separate questions will be addressed in two
pilot studies as described in the current proposal.

In PD patients: To investigate the effect of Levodopa on postural responses
after translational perturbations. These outcomes will be helpful to decide
whether patients in the cohort study should be measured in the ON or OFF
medication state. In addition, the results will provide more information about
the role of the dopaminergic system in postural stability in PD patients.
In stroke patients: To determine the effect of Weight Bearing Asymmetry (WBA)
on postural stability. Since WBA is common in stroke patients, the outcomes are
useful for the interpretation of the results of the cohort study. Furthermore,
the reusults give more insight in the mechanisms of balance control in stroke
patients.

Experimental study with repeated measurements.

Patients will have to visit the hospital for a balance assessment (1 visit for
stroke AND 2 visits for PD). During the balance assessment participants will be
exposed to balance perturbations by sudden translations of the support surface.
The risks of participating in the balance assessment are very small, since
rails are mounted around the balance platform and participants wear a safety
harness. PD patients will be measured in their medication OFF state once, which
means that they have to skip one dose of dopaminergic medication. This
procedure is completely safe and internationally accepted. After the
assessments, that will be planned in the morning, patients can take the missed
medication dose and continue the regular medication schedule.