Rehabilitative orthotics evaluation in children with diplegic cerebral palsy: kinematics and kinetics.

Ankle foot orthoses (AFOs) are prescribed for ambulatory children with spastic diplegia to improve biomechanical alignment and functional capability. The purpose of this study was to employ quantitative motion analysis of the lower extremity to investigate two rehabilitative orthotics. The effects of hinged ankle foot orthoses (HAFO) and dynamic ankle foot orthoses (DAFO) for joint ankle management in children with cerebral palsy were compared. Sixteen (16) independently ambulatory children with a diagnosis of spastic diplegic cerebral palsy (7.5 +/- 2.9 yrs.) were included in the study. The biomechanical effects of two AFO designs were compared to barefoot using a 3-D motion analysis system. Significant differences between braced and unbraced conditions were found in peak ankle dorsiflexion, and peak ankle plantarflexion, knee stance peak flexion, knee swing peak flexion, hip stance peak flexion, and peak ankle plantarflexion moment (p < 0.01). Differences between the HAFO and DAFO were not seen in the kinematic and kinetic metrics. Further development of dynamic testing is suggested in order to advance our understanding of orthotic intervention. The value of quantitative description of gait dynamics is clearly indicated for rehabilitative application.

Constrained RLS algorithm for narrow band interference rejection from EEG signal during CES.

The filtering of signals in the presence of a narrow-band interference noise is a common problem in biomedical signal processing. A double adaptive band-rejection filter is applied to an electroencephalographic (EEG) signal corrupted by a double narrow-band white Gaussian noise during cranial electrical stimulation (CES). The multiple adaptive IIR digital band-rejection filters are designed by the pole-zero placement on the unit circle method using a unique second-order filter structure. Multiple band-rejection filters (of order 2N) can be designed by cascading N second-order band-rejection filters. The coefficients of the multiple band-rejection filters are calculated by convoluting the coefficients of the second-order band-rejection filters. The pole-zero placement on the unit circle method relates the coefficients of the filter through fundamental coefficients that are assumed to be independent. These coefficients are updated through the recursive least-squares (RLS) algorithm. Unlike other RLS based multiple adaptive band-rejection filters, the new constrained RLS (CRLS) multiple adaptive HR band-rejection filter truly adapts its zeros and poles.

Spectral analysis of surface electromyography (EMG) of upper esophageal sphincter-opening muscles during head lift exercise.

Although recent studies have shown enhancement of deglutitive upper esophageal sphincter opening in healthy elderly patients performing an isometric/isotonic head lift exercise (HLE), the muscle groups affected by this process are not known. A shift in the spectral analysis of surface EMG activity seen with muscle fatigue can be used to identify muscles affected by an exercise. The objective of this study was to use spectral analysis to evaluate surface EMG activities in the suprahyoid (SHM), infrahyoid (IHM), and sternocleidomastoid (SCM) muscle groups during the HLE. Surface EMG signals were recorded continuously on a TECA Premiere II during two phases of the HLE protocol in eleven control subjects. In the first phase of the protocol, surface EMG signals were recorded simultaneously from the three muscle groups for a period of 20 s. In the second phase, a 60 s recording was obtained for each of three successive trials with individual muscle groups. The mean frequency (MNF), median frequency (MDF), root mean square (RMS), and average rectified value (ARV) were used as spectral variables to assess the fatigue of the three muscle groups during the exercise. Least squares regression lines were fitted to each variable data set. Our findings suggest that during the HLE the SHM, IHM, and SCM muscle groups all show signs of fatigue; however, the SCM muscle group fatigued faster than the SHM and IHM muscle groups. Because of its higher fatigue rate, the SCM muscle group may play a limiting role in the HLE.

Instantaneous postural stability characterization using time-frequency analysis.

Postural stability assessment is critical to a more accurate understanding of sway and balance control. The center of pressure (COP) metric has been shown to be a suitable output measure for time and frequency analysis. However, the center of pressure is a non-stationary signal. Standard time and frequency analysis methods may not be adequate for monitoring the dynamic changes in the center of pressure signal. In this study a time-frequency method, based on data-adaptive evolutionary spectral estimation, is applied to monitor the dynamic changes of the center of pressure in a non-stationary environment. Metrics including the instantaneous mean frequency (IMF), instantaneous spectral bandwidth (ISB), and instantaneous average power (IAP) are analyzed to characterize the center of pressure signal in both the anterior-posterior (AP) and the medial-lateral (ML) planes. Within the confines of this study, the IMF was found to be inversely proportional to IAP. The inverse proportionality factors were calculated in both eyes-open and eyes-closed trials during upright quiet standing. These findings suggest that the time-frequency analysis provides instantaneous metrics which describe the amplitude changes and frequency shift of the center of pressure under a variety of environmental conditions, thus providing a more reliable quantification of postural control.

Effects of surface electrode size on computer simulated surface motor unit potentials.

Surface myoelectric signals are recorded in motor nerve conduction, fatigue and kinesiologic studies using discrete electrodes. Single site recordings have limited means to reduce cross-talk and to enhance timing and quantification of relative muscular activity. These limitations are compounded by the effects of the electrode size. A grid electrode would reduce some of these limitations. However, an optimum grid electrode requires detail examination of the effects of the size of individual electrodes and the interelectrode distance. The purpose of this study is to investigate the temporal and spatial effects of the electrode size on surface motor unit potentials (SMUP). Muscle fiber action potentials and surface electrodes are simulated by computer models. Peak to peak amplitude, the mean frequency of SMUP, and the muscle conduction velocity were calculated as functions of the size of the electrode. The random variations of these parameters due to systematic errors are also simulated and investigated.

Anatomical and technical considerations in surface electromyography.

Despite the technical and clinical limitations of surface EMG, it is essential in the physical medicine and rehabilitation field. Surface EMG has evolved from a secondary means of clinical assessment to a primary factor in determining and predicting clinical outcomes. Computer models of electrical muscular activity are currently implemented to assist in designing proper instrumentation and electrode with optimum dimensions. These models could be expanded to simulate pathological motor functions to help understand functional abnormalities even before clinical interventions. Currently, several groups all over the world are investigating the use of multichannel surface EMG. This technological advancement would have an immediate impact on several medical fields. For instance, tendon transfers are performed to improve function in peripheral nerve injury, brachial plexus lesion, spinal cord injury, and cerebral palsy. There are potential uses for multichannel surface EMG, both preoperatively and postoperatively. Preoperatively choosing the muscle for transfer has been largely based on clinical grounds. Multichannel surface EMG could give a more objective database to assess prognosis and determine which muscle to transfer. Postoperatively, multichannel surface EMG can provide a systematic way of assessing changes in gross muscle topography caused by the tendon transfer. Other applications of multichannel surface EMG would be for bony and soft tissue deformity from arthritis, heterotopic ossification, amputation, or burns. Multichannel surface EMG would allow clinicians to get a broader picture of the skeletal muscle activity despite the fact that it is physically impossible for the patient to assume the anatomic position used for traditional isolated electrode placement. Individuals with physical disabilities that affect their ability to assume the usual posture for electrophysiologic testing may benefit considerably from development of multichannel electrophysiologic testing. Patients with abnormalities of tone from various causes such as stroke, traumatic brain injury, and cerebral palsy are at times evaluated with kinesiologic EMG to assess motor control. Multichannel surface EMG could potentially give us much greater insight into motor control disorders.

Enhanced period-peak analysis of electro-encephalograms using a fast sinc function.

In an effort to reduce the memory space and processing time required by fast Fourier transforms, enhanced period-peak detection is investigated. The method is based on a combination of Fourier transforms and period-peak detection. The signal is considered as a train of truncated sinusoidal functions. Each truncated sinusoidal function is limited by two successive local extrema. The Fourier transform of the truncated sinusoidal function is a sinc function. The summation of these sinc functions yields an approximate frequency spectrum of the signal.

Potential and current density distributions of cranial electrotherapy stimulation (CES) in a four-concentric-spheres model.

Cranial electrotherapy stimulation (CES) has been successfully used for treatment of many psychiatric diseases. Its noninvasive nature is its major advantage over other forms of treatments such as drugs. It is postulated that the low electric current of CES causes the release of neurotransmitters. However, the current pathways have not been extensively investigated. In the following paper, analytical and numerical methods are used to determine the distribution of potential and current density in a four zone concentric spheres model of the human head when excited by two electrodes diametrically opposite to each other. Because of the azimuthal symmetry, which is assumed in this study, a two-dimensional (2-D) finite difference approximation is derived in the spherical grid. The current density distribution is projected around the center of the model, where the thalamus is modeled as a concentric sphere. All dimensions and electrical properties of the model are adapted from clinical data. Results of this simulation indicate that, in contrast to previous beliefs, a small fraction of the CES current does reaches the thalamic area and may facilitate the release of neurotransmitters.

Adaptive digital notch filter design on the unit circle for the removal of powerline noise from biomedical signals.

This paper investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz, three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared (CLMS) algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal.

Enhanced period-peak analysis of the electroencephalogram using a fast Sinc function.

EEG computer analysis is still not widely used in the clinic, and the need for advanced signal processing techniques is still warranted. The fast Fourier transform (FFT) is the method most frequently used for power spectrum estimation of the EEG. In an effort to reduce memory space and processing time required by the fast Fourier transform (FFT), a new method, the enhanced period-peak detection (EPPD), is investigated. The method is based on a combination of the Fourier transform (FT) and period-peak detection. The signal is considered as a train of truncated sinusoidal functions. Each truncated sinusoidal function is limited by two successive local extrema (a peak and a valley). The Fourier transform of the truncated sinusoidal function is the well known Sinc function. The summation of these Sinc functions yields an approximate frequency spectrum of the signal. The speed and performance of the FFT rely upon the number of data collected and the sampling frequency. On the other hand, the enhanced period-peak detection (EPPD) method does not require that the entire EEG data be stored. Only the extrema of the signal and time between the peaks are needed. Furthermore, the frequency resolution of the EPPD is independent of the number of data available and of the sampling frequency.

Frequency-domain digital filtering techniques for the removal of powerline noise with application to the electrocardiogram.

This paper presents two new local processing frequency-domain methods for the removal of powerline noise from electrophysiological signals. The first is based on an iterative division or a multiplication of a set of frequencies centered at 60 Hz. The second users a basic property of the natural logarithm to smooth the 60-Hz noise. Both methods are intended to reduce powerline noise without affecting the frequency spectrum of the signal in the regions surrounding 60 Hz. For illustration, these local processing methods are applied to artificial and real electrocardiographic (ECG) data and are compared to a fixed IIR notch digital filter which is designed by pole-zero placements on the unit circle. The performance of each method is measured by the error squared, which is the square of the difference between the original noise-free signal and the filtered noisy ECG. Finally, since the two methods are iterative processes, comparison of their rate of convergence to a predefined noise reduction level is considered.