Krzysztof Kręcisz

Attention Demand and Postural Control in Children with Hearing Deficit.

To elucidate the mechanisms responsible for deteriorated postural control in children with hearing deficit (CwHD), we measured center-of-pressure (COP) variability, mean velocity and entropy in bipedal quiet stance (feet together) with or without the concurrent cognitive task (reaction to visual stimulus) on hard or foam surface in 29 CwHD and a control group of 29 typically developing children (CON). The CwHD displayed an overall decreased postural performance as compared to the CON in the medial-lateral plane (p<0.05). Standing on foam pad revealed slower simple reaction time in the CwHD (p<0.05) while the results on hard surface were not different. The CwHD decreased (p<0.05) the amount of attention invested in posture during dual task which accounted for the need of more cognitive resources to handle two tasks simultaneously than controls. It was unmistakable that the intergroup differences emerged when the tasks performed were relatively novel and untrained: feet together, foam pad, and reaction time. All these tasks, while being very easy for the CON, made the CwHD deteriorate postural or cognitive performance. These results unravel the difficulty in reaching the consecutive developmental stages in the CwHD and call for specific therapeutic modalities that might facilitate this development.

Postural stability in young adults with down syndrome in challenging conditions

To evaluate postural control and performance in subjects with Down syndrome (SwDS), we measured postural sway (COP) in quiet stance in four 20-second tests: with eyes open or closed and on hard or foam surface. Ten SwDS and eleven healthy subjects participated, aged 29.8 (4.8) and 28.4 (3.9), respectively. The time-series recorded with the sampling rate of 100 Hz were used to evaluate postural performance (COP amplitude and mean velocity) and strategies (COP frequency, fractal dimension and entropy). There were no intergroup differences in the amplitude except the stance on foam pad with eyes open when SwDS had larger sway. The COP velocity and frequency were larger in SwDS than controls in all trials on foam pad. During stances on the foam pad SwDS increased fractal dimension showing higher complexity of their equilibrium system, while controls decreased sample entropy exhibiting more conscious control of posture in comparison to the stances on hard support surface. This indicated that each group used entirely different adjustments of postural strategies to the somatosensory challenge. It is proposed that the inferior postural control of SwDS results mainly from insufficient experience in dealing with unpredictable postural stimuli and deficit in motor learning.

Age-Related Impairment of Quality of Joint Motion in Vibroarthrographic Signal Analysis

Aging is associated with degenerative changes in articular surfaces leading to quantitative and qualitative impairment of joint motion. Therefore, the aim of this study is to evaluate an age-related quality of the patellofemoral joint (PFJ) motion in the vibroarthrographic (VAG) signal analysis. Two hundred and twenty individuals were enrolled in this study and divided into five groups according to age. The VAG signals were collected during flexion/extension knee motion using an acceleration sensor and described using four parameters (VMS, P1, P2, and H). We observed that values of parameters VMS, P1, and P2 increase in accordance with the age, but H level decreases. The most significant differences were achieved between the youngest and the oldest participants groups. Moreover, we show that parameters VMS, P1, and P2 positively correlate with age, contrary to negatively associated H parameter. Our results suggest that the impairment of joint motion is a result of age-related osteoarticular degenerative changes.

Vibroarthrography in the evaluation of musculoskeletal system - a pilot study.

BACKGROUND. Disorders of the articular surfaces are associated with impaired quality of joint motion and joint play. Crepitations are the hallmark clinical sign. This paper aims to present the possibilities of using vibroacoustic signal analysis in assessing the function of articular surfaces in the course of disorders of the knee and shoulder. MATERIAL AND METHODS. The study involved 30 people, 10 for each of the following disorders: patellar chondromalacia (Ch), meniscal tears (Mc), and degenerative changes of the glenohumeral joint (GH). A control group (K1-K3) was matched to each dysfunctional group. 6-second vibroacoustic signals (VAG) were recorded during motion in particular joints. The resulting time series were filtered (50-1000 Hz) and the following parameters were calculated: variance-mean-square (VMS), the mean of the four lowest and four highest values (R4) and the total spectral power density in the 50-250 Hz (P1) and 250-450 Hz (P2) ranges. RESULTS. Depending on the type of disorder, VAG signals in the dysfunctional groups were characterized by higher variability, amplitude and frequency than was the case in the control groups. This is reflected in the values of all parameters (VMS, R4, P1, P2), which were significantly higher in the Ch, Mc and GH groups compared to K1-K3. CONCLUSIONS. 1. Vibroarthrography can be a useful tool for accurate and objective assessment of the quality of joint motion. 2. The non-invasive nature of vibroarthrography allows the use of this method to monitor the effects of the treatment of joint structures.

Attentional demands associated with augmented visual feedback during quiet standing

To investigate how additional visual feedback (VFB) affects postural stability we compared 20-sec center-of-pressure (COP) recordings in two conditions: without and with the VFB. Seven healthy adult subjects performed 10 trials lasting 20 seconds in each condition. Simultaneously, during all trials the simple auditory reaction time (RT) was measured. Based on the COP data, the following sway parameters were computed: standard deviation (SD), mean speed (MV), sample entropy (SE), and mean power frequency (MPF). The RT was higher in the VFB condition (p < 0.001) indicating that this condition was attention demanding. The VFB resulted in decreased SD and increased SE in both the medial-lateral (ML) and anterior-posterior (AP) planes (p < .001). These results account for the efficacy of the VFB in stabilizing posture and in producing more irregular COP signals which may be interpreted as higher automaticity and/or larger level of noise in postural control. The MPF was higher during VFB in both planes as was the MV in the AP plane only (p < 0.001). The latter data demonstrate higher activity of postural control system that was caused by the availability of the set-point on the screen and the resulting control error which facilitated and sped up postural control.

Application of sEMG and Posturography as Tools in the Analysis of Biosignals of Aging Process of Subjects in the Post-production Age

Surface electromyography (sEMG) and posturography are some of the most useful tools applied in the assessment of the motor skills of humans. The scope and objective of this paper is to report on concurrent and synchronized application of the Kistler platform for postural balance and electromyography analysis (sEMG Noraxon) with the purpose of the registration of the bioelectric muscle tension of selected muscles (soleus, tibialis anterior). A random group of senior subjects aged 60–70 years, who participate in regular fitness program involving the formation of psychomotor activities (once a week) and focusing primarily on the motor coordination and low-intensity aerobic performance capacity was subjected to 4 tasks involving postural assessment. The results of the study were concerned with the analysis of the correlation between the sEMG and COP parameters and confirm the initial hypothesis regarding the existence of a positive correlation between the level of muscular coactivation (soleus, tibialis anterior) and the scatter parameters of COP.

Analysis and multiclass classification of pathological knee joints using vibroarthrographic signals

BACKGROUND AND OBJECTIVEnVibroarthrography (VAG) is a method developed for sensitive and objective assessment of articular function. Although the VAG method is still in development, it shows high accuracy, sensitivity and specificity when comparing results obtained from controls and the non-specific, knee-related disorder group. However, the multiclass classification remains practically unknown. Therefore the aim of this study was to extend the VAG method classification to 5 classes, according to different disorders of the patellofemoral joint.nnnMETHODSnWe assessed 121 knees of patients (95 knees with grade I-III chondromalacia patellae, 26 with osteoarthritis) and 66 knees from 33 healthy controls. The vibroarthrographic signals were collected during knee flexion/extension motion using an acceleration sensor. The genetic search algorithm was chosen to select the most relevant features of the VAG signal for classification. Four different algorithms were used for classification of selected features: logistic regression with automatic attribute selection (SimpleLogistic in Weka), multilayer perceptron with sigmoid activation function (MultilayerPerceptron), John Platts sequential minimal optimization algorithm implementation of support vector classifier (SMO) and random forest tree (RandomForest). The generalization error of classification algorithms was evaluated by stratified 10-fold cross-validation.nnnRESULTSnWe obtained levels of accuracy and AUC metrics over 90%, more than 93% sensitivity and more than 84% specificity for the logistic regression-based method (SimpleLogistic) for a 2-class classification. For the 5-class method, we obtained 69% and 90% accuracy and AUC respectively, and sensitivity and specificity over 91% and 69%.nnnCONCLUSIONSnThe results of this study confirm the high usefulness of quantitative analysis of VAG signals based on classification techniques into normal and pathological knees and as a promising tool in classifying signals of various knee joint disorders and their stages.