Alterations in postural control: the use of spectral analysis in stability measurement [Alterazioni del controllo posturale: utilità dell'analisi spettrale in stabilometria.]

Static posturography studies the frequency at which the center of gravity in the human body oscillates. There is no universal agreement as to the importance of this index or whether it is specific in identifying alterations in the postural control systems (vestibular, proprioceptive and visual). Nevertheless, some hypotheses appear generally accepted: a) visual information dominates; b) proprioception affects anterior-posterior oscillation; c) relatively low frequency body oscillation is affected by vestibular input while higher frequency oscillations are controlled by proprioceptive information. In order to check these hypotheses, four groups of patients underwent spectral analysis of bodily oscillations recorded with static posturography. The four groups of patients were similar in terms of age and broken down as follows: Group A-peripheral diabetic neuropathy (10 cases); Group B-diabetic neuropathy-free patients (10 cases); Group C-pure peripheral vestibulopathy (10 cases); Group D-normal subjects (20 cases). Analysis was performed dividing the frequency spectrum (FFT) into three groups: gr. I) 0.01-0.7 Hz; gr. II) 0.7-1 Hz; gr. III) > 1 Hz. Analysis of the spectra for Group A showed a significant increase in high frequency bodily oscillation (gr. III) with the eyes open in the anterior-posterior direction (M = 8.6 +/- 5.5; p < 0.05) and in the lateral direction (M = 4.0 +/- 2.0; p < 0.05); an increase was also found in both directions with the eyes closed (M = OCX II: 7.4 +/- 1.5; p < 0.05) (M = OCX III: 5.6 +/- 1.6; p < 0.01) (M = OCY II: 16.8 +/- 5.0; p < 0.05) (M = OCY II: 9.2 +/- 4.4; p < 0.05). In Group B the increase was limited to high frequency anterior-posterior oscillations (gr. III) at open eyes (M = 3.6 +/- 1.6; p < 0.05) and at closed eyes (M = 4.4 +/- 1.5; p < 0.05). In Group C there was an increase in high frequency lateral oscillations (gr. III) at open eyes (M = 4.2 +/- 0.5; p < 0.01) and panfrequency oscillations at closed eyes (M = OCX I: 47.7 +/- 5.6; p < 0.01) (M = OCX II: 23.2 +/- 4.9; p < 0.01) (M = OCX III: 7.2 +/- 2.3; p < 0.05). CONCLUSIONS: The diabetic proprioceptive deficit appears to lead to multiplanar destabilization at the medium-to-high frequency range. The labyrinthine deficit, on the other hand, appears to cause lateral destabilization at all frequencies. The method of analysis used appears to provide useful parameters with which to evaluate static posture since they can specifically identify alterations in orthostatic bodily control of various origins.