Litchy, William J.

This study presents the first in vivo intraoperative measurement of the kinetic properties of spastic human muscle. Despite slower relaxation in spastic biceps, the force-frequency relationship was similar to that of the healthy gracilis muscle. This suggests that spasticity does not substantially alter frequency-dependent force summation, possibly due to similar fiber-type compositions and limited changes in calcium handling or myosin isoforms in human spastic muscle.

AbstractThe sliding filament theory explains skeletal muscle fibre force change as a function of length based on the overlap of actin and myosin filaments. Although this length‐tension (LT) relationship has been well investigated in animal models, it is not known whether this microscopic sarcomere LT property can be scaled up five orders of magnitude to explain the LT behaviour of a long human muscle such as the gracilis. The goal of this study is to validate the sarcomere LT curve in humans based on human filament length combined with in vivo experimental data. Intraoperative measurements of maximal tetanic force and muscle‐tendon unit length at four different joint configurations (JC) were obtained from 19 patients undergoing free functioning muscle transfer surgery. With physiologically measured fibre length and estimated sarcomere shortening resulting from tendon compliance, we show that 79.7% variance in isometric force data is explained by a simple human sarcomere LT model. This study demonstrates that the human whole muscle LT relationship can be modelled by the sliding filament theory given patient‐specific fibre length, filament length, tendon compliance and sarcomere shortening. imageKey points Whole human gracilis muscle isometric length‐tension relationships were measured in the operating room. Grouped whole muscle raw length‐tension curves showed no obvious form. The width of each experimental length‐tension curve was highly variable across subjects and used to predict fibre length (serial sarcomere number). After whole muscle length‐tension curves were normalized to each patient's serial sarcomere number, the whole human muscle length‐tension curve was well predicted by the sliding filament theory.

ABSTRACTIntroduction/AimsNeuromuscular ultrasound (NMUS), initially performed by physicians, is increasingly performed by technicians in many electrodiagnostic (EDX) laboratories for certain studies under physician supervision. The aims of this study were to determine: (1) the reproducibility of nonphysician sonographers' assessments of the median nerve and (2) the need for ongoing training to maintain the reproducibility and reliability of median nerve ultrasound assessments.MethodsThe median nerve was examined sonographically in a healthy volunteer by 12 nonphysicians on 3 separate occasions: Day 1 and then 2 weeks (Day 2) and 4 months (Day 3) later. Cross‐sectional area (CSA) and wrist‐to‐forearm ratios (WFRs) were calculated each time. Sonographers were retrained prior to Day 2. Reproducibility and reliability were determined using coefficients of variation calculated for each characteristic for each day and each nonphysician sonographer, comparing performance across the 3 time points.ResultsThere was overall less variation for each characteristic (wrist CSA, forearm CSA, and WFR) on Day 2 compared to Day 1 (coefficients of variation 3.0%, 5.4%, and 5.7% vs. 8.8%, 15.5%, and 11.3%, respectively), both when viewed at the group and individual levels, indicating an improvement in reproducibility and reliability after the retraining session. The improvement was similar for Day 3.DiscussionThis study demonstrates the need for training and subsequent retraining sessions to ensure the reproducibility and reliability of NMUS measurements in the median nerve.

ABSTRACTCavin‐4 was identified as a potential autoantigen for immune‐mediated rippling muscle disease (iRMD). To validate this, we developed and tested various immunoassays, including a cell‐based assay (CBA), cavin‐4 recombinant protein ELISA, and multi‐peptide ELISA. Among 19 iRMD patients, all exhibited muscle rippling, and 13 had percussion‐induced mounding. All immunoassays demonstrated clinical and analytical specificities greater than 95%. The protein ELISA had the highest sensitivity (94.7%) and specificity (99.9%), outperforming CBA (sensitivity 89.5%, specificity 99.6%) and the multi‐peptide ELISA (sensitivity 79.0%, specificity 97.2%). Our results suggest that the cavin‐4 protein ELISA is a promising tool for high‐throughput clinical testing in iRMD.