Biomedical subjects

Maria Stokes

Publications and source records attributed to Maria Stokes.

4 recordsLinked to original sources

PubMed2006

Abdominal muscle size and symmetry in normal subjects.

This study was undertaken to establish normal reference ranges for abdominal muscle size and symmetry and to examine the effects on these of gender and age. We studied 123 subjects, consisting of 55 men (aged 21-72 years) and 68 women (aged 20-64 years). Real-time ultrasound imaging of the abdominal muscles was performed. Thickness of internal and external oblique (IO, EO), transversus abdominis (TA), and rectus abdominis (RA), and cross-sectional area (CSA) of RA were measured, and absolute and relative muscle thickness (percent total muscle thickness), order of thickness, and symmetry (percent difference between sides) were determined. Males had significantly larger muscles than females and size was poorly correlated with age. The pattern of relative muscle thickness was RA > IO > EO > TA. Symmetry for total absolute thickness of all three lateral muscles was 8%-9% (mean) but for individual muscles there was asymmetry of absolute size (13%-24%), whereas relative thickness was symmetrical for all muscles. These findings provide robust reference data for the abdominal muscles in normal males and females in order to enable comparison with clinical groups to assess abnormalities and establish sensitivity for evaluating the effectiveness of interventions.

Abdominal Muscles↗

PubMed2004

Adaptive BCI based on variational Bayesian Kalman filtering: an empirical evaluation.

This paper proposes the use of variational Kalman filtering as an inference technique for adaptive classification in a brain computer interface (BCI). The proposed algorithm translates electroencephalogram segments adaptively into probabilities of cognitive states. It, thus, allows for nonstationarities in the joint process over cognitive state and generated EEG which may occur during a consecutive number of trials. Nonstationarities may have technical reasons (e.g., changes in impedance between scalp and electrodes) or be caused by learning effects in subjects. We compare the performance of the proposed method against an equivalent static classifier by estimating the generalization accuracy and the bit rate of the BCI. Using data from two studies with healthy subjects, we conclude that adaptive classification significantly improves BCI performance. Averaging over all subjects that participated in the respective study, we obtain, depending on the cognitive task pairing, an increase both in generalization accuracy and bit rate of up to 8%. We may, thus, conclude that adaptive inference can play a significant contribution in the quest of increasing bit rates and robustness of current BCI technology. This is especially true since the proposed algorithm can be applied in real time.

Algorithms↗

PubMed2004

Cognitive tasks for driving a brain-computer interfacing system: a pilot study.

Different cognitive tasks were investigated for use with a brain-computer interface (BCI). The main aim was to evaluate which two of several candidate tasks lead to patterns of electroencephalographic (EEG) activity that could be differentiated most reliably and, therefore, produce the highest communication rate. An optimal signal processing method was also sought to enhance differentiation of EEG profiles across tasks. In ten normal subjects (five male), aged 29-54 years, EEG activity was recorded from four channels during cognitive tasks grouped in pairs, and performed alternately. Four imagery tasks were: spatial navigation around a familiar environment; auditory imagery of a familiar tune; and right and left motor imagery of opening and closing the hand. Signal processing methodology included autoregressive (AR) modeling and classification based on logistic regression and a nonlinear generative classifier. The highest communication rate was found using the navigation and auditory imagery tasks. In terms of classification performance and, hence, possible communication rate, these results were significantly better (p < 0.05) than those obtained with the classical pairing of motor tasks involving imaginary movements of the left and right hands. In terms of EEG data analysis, a nonlinear classification model provided more robust results than a linear model (p << 0.01), and a lower AR model order than those used in previous work was found to be effective. These findings have implications for establishing appropriate methods to operate BCI systems, particularly for disabled people who may experience difficulty with motor tasks, even motor imagery.

Adult↗

PubMed2003

Effects of knee joint angle and tilt table incline on force distribution at the feet and supporting straps.

OBJECTIVE: To investigate the effects of tilt table incline and knee flexion angle on the degree of weight bearing and forces exerted across the supporting straps. DESIGN: A quantitative and exploratory study to investigate the effects of a mechanical procedure. SETTING: Physiotherapy gymnasium. SUBJECTS: Twelve healthy subjects (9 female, 3 male) aged 22-45 years. INTERVENTIONS: Subjects stood on a tilt table, on two occasions, with simulated contractures of 10 degrees and 40 degrees knee flexion. Nine tilt angles, between 10 degrees and 90 degrees, were maintained for 1 minute each in random order. MAIN OUTCOME MEASURES: Force was recorded from single-point load cells placed under the feet, and at knee and chest straps. RESULTS: The degree of simulated knee contracture (10 degrees or 40 degrees) influenced the distribution of forces at different recording sites. Weight bearing increased with table incline and was significantly less with the 40 degrees than the 10 degrees knee angle (p < 0.001). Conversely, forces across the knee straps were systemically higher with the 40 degrees knee angle (p < 0.0001). The effects were accentuated by greater body weight. Forces across the chest strap also increased with tilt and were significantly larger with the 40 degrees knee angle (p < 0.05). CONCLUSIONS: The relationships between table incline, angle of knee flexion and distribution of forces generated during tilt table standing have been quantified and described. Standing with flexed knees involved less weight bearing under the feet and greater force exerted across the supporting straps. These effects were more pronounced at the higher knee angle and with greater body weight, and could be modified by reducing table incline.

Adult↗