Effect of dual task performance on postural stability in Parkinson´s disease patients. A pilot study.

Introduction

Parkinson‘s disease (PD) is a progressive degenerative disorder of the central nervous system (CNS). Its clinical manifestations include 4 cardinal signs: tremor, rigidity, bradykinesia and postural instability (Rossi et al., 2009). Postural instability represents a highly disabling and poorly treatable symptom that interferes with the ability to maintain balance and predisposes Parkinson´s disease (PD) patients to unexpected falls. Horak et al. (1992) found that patients exhibited little sway, but had altered postural responses due to excessive antagonist muscle tone and inflexibility in adapting to changing support conditions.

Many factors have been found to be associated with loss of balance and falling in PD patients (Ashburn et al 2001). However, the attention has been focused on the possible influence of dual task performance on postural stability (Morris et al., 2000; Marchese et al., 2003). Ashburn and Stack (2000) showed that greater postural sway was present in faller PD patients whilst completing a distracting cognitive task. This study investigates the influence on standing balance of dual task performance in patients with PD.

Methods

Subjects.

Six PD patients (68.1 years; Hoehn & Yahr 1,5-3; 3 males) and six control subjects (64.7 years; 4 males) participated in this study.

General procedures.

Was performed a static posturographic analysis to verify whether balance was similarly affected in PD patients and control subjects (CTRL) during concomitant performance of relatively simple cognitive tasks. A force plate (Kistler 9286) was used to analyze the following variables:

1. Center of mass (CoM) Area corresponding to the the area of the ellipse of inertia of the computed CoM points (this parameter gives an indication of the amplitude of body sway);
2. Trace length corresponding to the distance covering the successive positions of the moving CoM;
3. Mean radius is defined as the average distance covered by the CoM from the initial position of the center of gravity of the CoM that describes the radius of a circumference;
4. Mean speed represents the average velocity of the CoM displacement;
5. Mediolateral (X) range represents the CoM displacement on the coronal plane (right to left);
6. Anteroposterior (Y) range represents the CoM displacement on the sagittal plane (anterior to posterior).

Subjects were asked to maintain a stable posture (foots 4 cm apart and the arms relaxed in their sides) during the performance of the balance tests. They were tested in four randomized conditions: a) eyes open (EO), b) eyes closed (EC), c) EO during counting backward aloud in multiples of three (EOcog), d) EC during counting backward aloud in multiples of three (ECcog).

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Figure 1. Example of a subject CoM trace in the four experimental conditions (EO, EC, EOcog and ECcog).

Statistical analysis.

To assess the effect of cognitive task on postural control, ECcog and EOcog values were normalized in relation to EO and EC values, respectively, and a two way repeated measures (RM) ANOVA (condition -EO, EC, EOcog and ECcog – and group -PD and CTRL-) was performed using SPSS  software (v. 15.0). The level of significance was 0.05.

Results

The ANOVA-RM showed significant differences between groups in the CoM area (p= 0.007), and mean radius (p= 0.005). The post-hoc analysis reflected significant differences between PD and CTRL in the ECcog (p? 0.05) and a trend in the EOcog (p= 0.11) for the CoM area. In relation to the Mean radius, the post-hoc analysis showed significant differences between PD and CTRL in the EOcog (p? 0.05) and a trend in the ECcog (p= 0.09). Differences between conditions were not found.

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Figure 2. Effect of dual-task performance in PD patients and CTRL subjects during balance control. (*) p? 0.05
Discussion.

This study has shown that the effect of dual-task performance on standing posture was different between PD patients and control subjects. Our results are consistent with findings from previous studies (Morris et al., 2000; Marchese et al., 2003). According to Morris et al. (2000) a concomitant verbal–cognitive task significantly deteriorated postural stability in PD patients. Impaired dual-task performance has been also documented during gait in PD patients (Bond and Morris, 2000; Morris et al., 1996). It has been suggested that PD patients use attentional strategies to compensate their balance problems due to defective basal ganglia mechanism (Morris et al., 2000). It has been postulated that during dual-task performance PD patients have reduced attentional capabilities so that their cortical control is less effective and the balance problems are revealed (Marchese et al., 2003).  However, on the other hand, Lajoie et al. (1993) observed a dual task decrement of mental performance that was attributed to the hierarchical functional priority of balance control. In this way, we did not control the cognitive performance of the participants, and we did not know the level of the attentional demands imposed to each subject. It could be a factor that triggers a greater variability in the results observed in our study.
In summary, we have observed impaired dual-task performance in PD patients in comparison with CTRL subjects during balance control. This finding has some implications for the strategies to be used in reducing the risk of fall in PD.

References

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