Low and high frequency fluctuations in center of pressure signals can detect postural deficits in idiopathic Parkinson’s disease patients

Deterioration of postural control is one of the cardinal symptom in Parkinson’s disease patients. It is also related to their risk of falls and loss of independence. In this study we have explored Empirical Mode Decomposition (EMD) method to unravel the low and high frequency fluctuations in center of pressure (COP) signals collected from standardized Sensory Organization Testing (SOT) in Parkinson’s disease patients. SOT can objectively measure postural control by assessing patient’s ability to effectively use his/her visual, vestibular, and proprioceptive information. A total of sixty Parkinson’s disease patients participated in this study (age = 68.5 ± 9.4; 44 males and 16 females). The participants performed SOT in both the “on” and “off” medication states. We found that fallers have significantly higher fluctuations in medial-lateral direction for SOT condition C6 (p=0.0001) during ON medication state. We also found that fallers have significantly higher weight asymmetric index than non-fallers (p<0.05) during both ON and OFF medication states. We found that Late PD patients have significantly higher high frequency fluctuations for VEST ratio in anterior-posterior (AP) direction (p=0.0031) and also significantly higher high frequency fluctuations in medial-lateral (ML) direction of SOT conditions C5 (p=0.001). We also found that Late PD patients had significantly lower complexity in VEST ratio. Also fallers were found to have significantly lower complexity in VEST ratio (p<0.001). In summary, low and high frequency fluctuations are sensitive measures to detect postural deficits in fallers versus non-fallers and also among early versus late PD patients. Non-linear signal analysis techniques such as EMD can detect peculiar postural deficits in idiopathic Parkinson’s disease patients.