The postural stability of stroke patients with hemiplegia was studied using a stabilometric platform with optokinetic stimulation (OKS). Four patients who could maintain a sitting posture without assistance were recruited. The patients were asked to sit quietly on a stabilometric platform fixed on a stool in a dim room. For OKS, a pattern of random dots was projected onto a screen placed 100 cm in front of the subjects, and was moved continuously in either horizontal direction with a velocity of 20º/s. The same pattern without any movement was presented as a control condition. In each condition, the total length of the sway path (SP), the circumferential area (CA), and the center of pressure position (CoP) along the right-left (x) and antero-posterior (y) axes were examined. The slope of the linear regression applied to the CoP change along the x-axis was used for the evaluation of the OKS effect (slope of CoP). Spectral analysis of body sway in the x-and y-axes was performed using fast Fourier transform (FFT). Power spectra of body sway were evaluated by comparing powers for three frequency bands: 0.01-0.1 1 Hz (Band 1), 0.1-1.0 Hz (Band 2) and 1.0-10 Hz (Band 3).
The SP and CA of the control subjects showed no significant difference for any pair of stimulus conditions. In CVA patients, however, the CA tended to be larger during ipsi-paralysis OKS than contra-paralysis OKS, while the SP showed no significant difference. The slope of CoP tended to shift to the ipsi-paralysis side during ipsi-OKS, while no clear shift was observed in contra-OKS (p < 0.05). Spectral analysis of x-axis body sway showed that the power for Band 1 during ipsi-OKS was larger than during contra-OKS (p < 0.05), while the power for Band 2 during ipsi-OKS was smaller than during contra-OKS (p < 0.05). The results suggest that the CoP shift during ipsi-paralysis OKS might be attributable to a relatively low contribution of the visual system to posture control.