Ronald H. Gabel

The effects of signal conditioning on the statistical analyses of gait EMG

Ensemble averaged EMG profiles generated for leg muscles during gait have been used to clinically assess disease or injury. Several of the methods that have been reported for conditioning gait EMG signals were compared using data collected from clinically normal subjects walking on a treadmill. Specifically investigated were the effects of filtering and the quantity of data averaged upon several statistical tests that measure the variability of, or differences between, EMG profiles. Our results suggest that the variance ratio (VR) provides a reasonable test of data variability because of its modest sensitivity to both the degree of filtering and the amount of data averaged. They also suggest that of the comparison statistics: Pearsons r, the Kolmogorov-Smirnov T test and the ANOVA F ratio, the T test was the most reliable in detecting differences between given profiles for all test conditions. However, recognition of this ability of the T test must be tempered by the knowledge that while obvious EMG signal differences did exist, observable functional differences in gait did not. The relationship between statistically similar/dissimilar EMG patterns and clinically functional/dysfunctional gait patterns needs to be established. In addition, since all of the test statistics studied were affected to some degree by filtering and averaging, care should be used when comparing statistical results from separate studies unless it is known that the studies were conducted under similar conditions, including data processing. To that end, we recommend that at least 20 strides be used in the averaging process since the statistics we tested have reached or are asymptotically approaching their final values by this point.

A gait analyzer/trainer instrumentation system☆

Abstract A device is described which permits the collection of numerous temporal and distance factors of gait. The device, which utilizes a microprocessor and instrumented walkway, was designed to make practical the routine clinical evaluation of the gait parameters. The self-contained clinical device, which can be made portable, does not require the attachment of any apparatus to the patient.

Some characteristics of laminar flow velocity spectra detected by a 20 MHz pulsed ultrasound Doppler.

For the purpose of improving accuracy of noninvasive flow measurements in small (1-2 mm diameter) blood vessels, an existing 20 MHz pulsed ultrasound Doppler velocimeter (PUDVM) has been augmented to allow fast Fourier transformation (FFT) of its Doppler shift signal. The modified instrument was used to collect velocity spectra for a benchtop test section delivering precise Poiseuille flows at velocities in the range of physiological interest. The velocity spectra demonstrated a substantial degree of broadening, much of which was attributable to the geometry of the finite sample volume size. Several spectral indices were studied as a function of flow field variables. Results showed that the intensity-weighted mean Doppler shift frequency, when converted to its corresponding velocity vM, agreed very closely with the theoretically predicted local fluid velocity. Measurement linearity and repeatability were evaluated for a number of system variables, indicating that FFT performance was essentially unaffected by several parameters capable of causing major degradation of (phasic) Doppler shift signals produced by conventional zero-crossing-counter circuitry. As presently configured, the augmented PUDVM instrument is fully capable of detailed flow field mapping in small subcutaneous vessels such as human digital arteries.

Insertion of fine-wire electrodes does not alter EMG patterns in normal adults

Abstract Dynamic electromyography (EMG) utilizes either surface or fine-wire intramuscular electrodes to collect data on muscle activity. The question arises whether or not insertion of fine-wire electrodes alters the patterns they are intended to reflect. This study was designed to evaluate the affect of fine-wire electrode insertion on muscle activity during gait in normal adults without muscle tone abnormalities by comparing ensemble-averaged surface EMG patterns and variance ratios (VR) before and after fine-wire electrode insertion. Pearsons correlation coefficients (r) and variance ratios (VR) were determined to assess the degree of similarity between pre- and post-insertion surface EMG patterns and the degree of repeatability of the muscle activity respectively. The ensemble-averaged signals reflect a high degree of pattern similarity as evidenced by high r values (usually greater than 0.90). Pre- and post-insertion VRs are similar. The low mean VRs indicate reasonable reproducibility for both pre- and post-insertion. We concluded that fine-wire electrodes had no significant affect on muscle activity during gait as measured by surface EMG signals under our conditions in normal adults.

Transcutaneous blood flow measurements in arteries of the human hand.

Technical advances in twenty MHz pulsed ultrasonic Doppler velocimetry (PUDVM) permit increasingly accurate measurements of blood flow in small vessels. This study applied advanced twenty MHz PUDVM methods to the transcutaneous, noninvasive quantitation of blood flow in arteries of the human hand. One hundred forty-four measurements were completed bilaterally in the digital arteries of all fingers and in the distal radial and ulnar arteries of the forearm. The data were averaged by artery for maximum velocity and average volumetric flow. The maximum velocity for digital and forearm arteries was about 20 centimeters per second and 50 centimeters per second, respectively. The average volumetric flow for these same arteries was about 0.02 cubic centimeters per second and 0.18 cubic centimeters per second, respectively. Statistical analysis demonstrated no differences between paired, contralateral arteries; within given fingers a difference occurred only between the radial and ulnar arteries of the index finger.