Todd R. Farrell

A Comparison of the Effects of Electrode Implantation and Targeting on Pattern Classification Accuracy for Prosthesis Control

The use of surface versus intramuscular electrodes as well as the effect of electrode targeting on pattern-recognition- based multifunctional prosthesis control was explored. Surface electrodes are touted for their ability to record activity from relatively large portions of muscle tissue. Intramuscular electromyograms (EMGs) can provide focal recordings from deep muscles of the forearm and independent signals relatively free of crosstalk. However, little work has been done to compare the two. Additionally, while previous investigations have either targeted electrodes to specific muscles or used untargeted (symmetric) electrode arrays, no work has compared these approaches to determine if one is superior. The classification accuracies of pattern-recognition-based classifiers utilizing surface and intramuscular as well as targeted and untargeted electrodes were compared across 11 subjects. A repeated-measures analysis of variance revealed that when only EMG amplitude information was used from all available EMG channels, the targeted surface, targeted intramuscular, and untargeted surface electrodes produced similar classification accuracies while the untargeted intramuscular electrodes produced significantly lower accuracies. However, no statistical differences were observed between any of the electrode conditions when additional features were extracted from the EMG signal. It was concluded that the choice of electrode should be driven by clinical factors, such as signal robustness/stability, cost, etc., instead of by classification accuracy.

Vaginal pressure-pain thresholds: initial validation and reliability assessment in healthy women.

Objectives Pelvic muscle pain syndromes are poorly understood and lack reliable diagnostic criteria. Furthermore, animal models suggest that somatic pain can influence the development of pelvic visceral pain dysfunction. To develop psychophysical measures to facilitate diagnosis of pelvic floor myofascial pain syndromes, this pilot was designed to preliminarily test the feasibility, reliability, and validity of pressure-pain thresholds (PPTs) to identify and quantify pelvic floor pain sensitivity. Methods We conducted a cross-sectional study of pelvic floor PPTs using 19 healthy women. Using a prototype vaginal pressure algometer, we measured PPTs and calculated intraclass correlations for short-term and intermediate-term reliability. Validity was assessed by correlating numerical rating scores for pain (0 to 100) at standard pressure levels applied to the right iliococcygeus muscle. Results The mean PPT of all pelvic floor sites was 1.52 kg/cm2 (SD=0.62), whereas thresholds of nonmuscle vaginal sites (anterior and posterior wall) were 1.65 kg/cm2 (SD=0.64). Pain numerical rating scores were positively correlated with stimulus intensity at the right iliococcygeus (Pearson r=0.61). Intraclass correlation demonstrated good short-term reliability at this same site for the first versus second, and second versus third measurements (0.75, 0.64); 1-week repeat reliability was also good for the right pubococcygeus, iliococcygeus, and obturator (0.69, 0.84, and 0.61, respectively), and both nonmuscle vaginal sites. Discussion These data suggest that PPTs may prove to be valid and reliable measures of pelvic floor somatic pain sensitivity in healthy women. Broader studies including a pelvic pain cohort should be conducted to corroborate these results and determine the techniques external validity and clinical relevance.

Comparative measurement of pelvic floor pain sensitivity in chronic pelvic pain.

OBJECTIVE: Women with pelvic pain conditions exhibit enhanced somatic pain sensitivity at extragenital sites. Whether comparable differences exist for pelvic floor or vaginal pain sensitivity is unknown. The present study was undertaken to estimate pelvic floor and vaginal pressure-pain detection thresholds both in women with pelvic pain and healthy women. METHODS: We conducted a cross-sectional study of pelvic floor and vaginal pain detection thresholds comparing 14 women with chronic pelvic pain to 30 healthy women without this condition. Using a prototype vaginal pressure algometer, we recorded continuous ascending pressure and determined each subjects pressure-pain threshold at each of eight paired pelvic floor sites and two adjacent vaginal sites. RESULTS: Mean pain detection thresholds for all 10 sites were significantly lower in women with pelvic pain compared with healthy controls (at right iliococcygeus, controls 1.73±0.60 kg/cm2 compared with women 0.96±0.38 kg/cm2, P<.001, other sites similar), and remained so after controlling for differences in patient age and menopausal status. Pelvic floor and vaginal site pain detection thresholds had moderate-to-strong correlations with each other (r=0.62–0.91). CONCLUSION: Chronic pelvic pain is associated with enhanced pelvic floor and vaginal pressure-pain sensitivity. LEVEL OF EVIDENCE: II

Pilot comparison of surface vs. implanted EMG for multifunctional prosthesis control

The classification accuracies of controllers utilizing EMG input from six surface and ten intramuscular recordings are compared. In addition, the effect of including autoregressive (AR) parameters into the input sets is examined. The average accuracies from four subjects are reported. It was observed that surface recordings based solely on amplitude data did not perform well (21.1% error) but adding AR coefficients increased this accuracy substantially (10.3%). The intramuscular recordings performed comparably to the surface recordings with AR coefficients using all ten (13.2%) and a smaller set of six (12.1%) channels of intramuscular data. The subset of six channels was selected using multinomial logistic regression. It was observed that adding the AR coefficients to the intramuscular recordings also produced an improvement in classification accuracy for the six (92.8%) and ten (93.7%) channel input sets. To our knowledge this is the first work in more than three decades that explores the use of intramuscular EMG for the control of upper-limb prostheses and this work demonstrates that it is possible to achieve a decrease in classification error of nearly 40% by using intramuscular recordings.