Objective: To investigate the posture reaction in patients with Parkinson’s disease (PD) and healthy age-matched controls when they were given quantitative backward perturbation.

Background: Although postural instability has large adverse influence on the ADL of PD patients, there is no established method for quantitative measurement of postural instability. Recently we developed a new apparatus imitating pull test for the quantitative assessment of postural instability. Using this apparatus, we are involved in elucidating the pathophysiology of postural instability.

Methods: Experiments were performed on eight PD patients (71.1 ± 4.7 y.o., UPDRS Part III 20.4 ± 12.3, Yahr stage 2.4 ± 1.0) and six healthy age-matched controls (75.0 ± 6.7 y.o.) (Figure 1). Subjects were worn a vest in which a lope was connected at the back and backward perturbation was given unexpectedly to the subjects at standing by suddenly putting a heavy bob attached at the other end of the lope (Figure 2). The minimum weight load for the induction of stepping reaction was measured. During the experiment surface EMGs of tibialis anterior muscle (TA) and soleus muscle were recorded. The onset time of trunk movement by the heavy bob was identified by an accelerometer attached at the back.

Results: The minimum weight load for stepping was 1.7 ± 0.8 kg in PD patients and 1.8 ± 0.7 kg in the controls, showing no significant change. In PD patients, the minimum weight load for stepping did not correlate with the degree of Yahr stage (Figure 3) nor the degree of UPDRS Part III (Figure 4). In the controls, TA activity started 180 ± 60 msec after the onset of trunk movement (Figure 5); whereas in PD patients, trunk movement started 170 ± 330 msec after the onset of TA activity (p<0.05) (Figure 6).

Conclusions: We were unable to make a quantitative assessment of postural instability by measuring minimum weight load for stepping. The present result that backward perturbation induced TA activity at a different timing between PD patients and controls indicate that posture reaction in PD patients may be performed in different manners from those in controls.

References: Horak F and Nashner L. Central programming of postural movements: adaptation to altered support-surface configurations. J Neurophysiol 55: 1369-1381, 1986. Chandler J, Duncan P, Studenski S. Balance performance on the postural stress test: comparison of young adults, healthy elderly, and fallers. Phys Ther 70: 410-415, 1990.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-difference-in-posture-reaction-against-backward-perturbation-between-patients-with-parkinsons-disease-and-healthy-controls/