Distinguishing reflex from non-reflex responses elicited by transcutaneous spinal stimulation targeting the lumbosacral cord in healthy individuals.

Transcutaneous spinal stimulation (TSS) studies rely on the depolarization of afferent fibers to provide input to the spinal cord; however, this has not been routinely ascertained. Thus, we aimed to characterize the types of responses evoked by TSS and establish paired-pulse ratio cutoffs that distinguish posterior root reflexes, evoked by stimulation of afferent nerve fibers, from motor responses, evoked by stimulation of efferent nerve fibers. Twelve neurologically intact participants (six women) underwent unipolar TSS (cathode over T11-12 spinal processes, anode paraumbilically) while resting supine. In six participants, unipolar TSS was repeated 2-3 months later and also compared to a bipolar TSS configuration (cathode 2.5 cm below T11-12, anode 5 cm above cathode). EMG signals were recorded from 16 leg muscles. A paired-pulse paradigm was applied at interstimulus intervals (ISIs) of 25, 50, 100, 200, and 400 ms. Responses were categorized by three assessors into reflexes, motor responses, or their combination (mixed responses) based on the visual presence/absence of paired-pulse suppression across ISIs. The paired-pulse ratio that best discriminated between response types was derived for each ISI. These cutoffs were validated by repeating unipolar TSS 2-3 months later and with bipolar TSS. Unipolar TSS evoked only reflexes (90%) and mixed responses (10%), which were mainly recorded in the quadriceps muscles (25-42%). Paired-pulse ratios of 0.51 (25-ms ISI) and 0.47 (50-ms ISI) best distinguished reflexes from mixed responses (100% sensitivity, > 99.2% specificity). These cutoffs performed well in the repeated unipolar TSS session (100% sensitivity, > 89% specificity). Bipolar TSS exclusively elicited reflexes which were all correctly classified. These results can be utilized in future studies to ensure that the input to the spinal cord originates from the depolarization of large afferents. This knowledge can be applied to improve the design of future neurophysiological studies and increase the fidelity of neuromodulation interventions.

Pendulum test parameters are useful for detecting knee muscle hypertonia and quantifying response to an intrathecal baclofen bolus injection.

Our objective was to determine which pendulum test parameters are useful for detecting hypertonia in the knee muscles and assessing the group and individual responses to intrathecal baclofen (ITB) bolus injection among prospective pump recipients. We included 15 neurological patients with lower limb hypertonia (mainly spinal cord injury, n  = 7) and collected data the day before (baseline), and 2.5 and 5.0 h after the 50-µg ITB bolus injection. For comparison, data were collected in 15 healthy controls. The average over six test repetitions was obtained for the number of oscillations, swing time (SwingT), amplitudes of the first flexion and extension, maximum angular velocities of the first flexion (F1V) and extension (E1V), relaxation index, and damping coefficient (DampC). Across the patient group, all pendulum parameters indicated a significant decrease in hypertonia from baseline to postinjection (analysis of variance P  ≤ 0.004), except DampC. On the basis of the cutoffs from the receiver operating characteristic curve, all parameters were good or excellent discriminators of hypertonia in patients from normotonia in controls (area under the curve ≥0.85), with the highest sensitivity for SwingT and E1V (≥93%). Furthermore, all parameters except F1V revealed a significant shift from preinjection hypertonia to postinjection normotonia among patients (McNamar test P  ≤ 0.002, DampC excluded due to missing data), with the greatest responsiveness for E1V and relaxation index (≥73%). The results confirm the overall usefulness of pendulum test parameters in this patient population and indicate that some parameters are better at detecting hypertonia (SwingT, E1V) whereas others (E1V, relaxation index) are more responsive to the ITB injection.

The contribution of walking speed versus recent stroke to temporospatial gait variability.

BACKGROUND: Inconsistent results have been reported for temporospatial gait variability after stroke. Given the large differences in gait speed across stroke subjects and relative to healthy controls, it is not clear which changes in temporospatial gait variability can be ascribed to the walking speed during gait evaluation versus the consequences of stroke. RESEARCH QUESTIONS: Does temporospatial gait variability differ between (1) stroke subjects grouped in clinically-relevant functional ambulation classes, (2) the paretic and non-paretic legs within each class, and (3) stroke and healthy subjects after controlling for gait speed? METHODS: Stroke subjects were evaluated at their comfortable speed < 2 months post-onset and classified into the household (<40 cm/s, n = 38), limited-community (40-80 cm/s, n = 35), and full-community (>80 cm/s, n = 14) walkers. Coefficients of variation (CVs) for paretic and non-paretic stance, initial double-support, and single-support times, step length, step cadence, and step width were compared across the stroke ambulation classes and between the two legs. For the parameters with significantly different CVs between stroke subjects and 33 age-matched controls walking at very-slow and free speeds, a 1-way ANCOVA was used with the gait speed as a covariate. RESULTS: For most step parameters, CVs were greater in slower stroke ambulation classes except for the smaller step width CV. The differences between the paretic and non-paretic legs emerged in slower walkers only. After controlling for the gait speed, CVs of stroke subjects no longer significantly differed from controls walking at very-slow speed. With controls walking at free speed, however, CVs for the paretic and non-paretic single-support times and the non-paretic step time remained significantly different. SIGNIFICANCE: Gait is more variable at slower speeds both in stroke subjects and healthy controls. After accounting for the free gait speed, the increased variability of only a few temporal parameters may be attributed to a recent stroke.

Neuromodulation with transcutaneous spinal stimulation reveals different groups of motor profiles during robot-guided stepping in humans with incomplete spinal cord injury.

Neuromodulation via spinal stimulation has been investigated for improving motor function and reducing spasticity after spinal cord injury (SCI) in humans. Despite the reported heterogeneity of outcomes, few investigations have attempted to discern commonalities among individual responses to neuromodulation, especially the impact of stimulation frequencies. Here, we examined how exposure to continuous lumbosacral transcutaneous spinal stimulation (TSS) across a range of frequencies affects robotic torques and EMG patterns during stepping in a robotic gait orthosis on a motorized treadmill. We studied nine chronic motor-incomplete SCI individuals (8/1 AIS-C/D, 8 men) during robot-guided stepping with body-weight support without and with TSS applied at random frequencies between 1 and up to 100 Hz at a constant, individually selected stimulation intensity below the common motor threshold for posterior root reflexes. The hip and knee robotic torques needed to maintain the predefined stepping trajectory and EMG in eight bilateral leg muscles were recorded. We calculated the standardized mean difference between the stimulation conditions grouped into frequency bins and the no stimulation condition to determine changes in the normalized torques and the average EMG envelopes. We found heterogeneous changes in robotic torques across individuals. Agglomerative clustering of robotic torques identified four groups wherein the patterns of changes differed in magnitude and direction depending mainly on the stimulation frequency and stance/swing phase. On one end of the spectrum, the changes in robotic torques were greater with increasing stimulation frequencies (four participants), which coincided with a decrease in EMG, mainly due to the reduction of clonogenic motor output in the lower leg muscles. On the other end, we found an inverted u-shape change in torque over the mid-frequency range along with an increase in EMG, reflecting the augmentation of gait-related physiological (two participants) or pathophysiological (one participant) output. We conclude that TSS during robot-guided stepping reveals different frequency-dependent motor profiles among individuals with chronic motor incomplete SCI. This suggests the need for a better understanding and characterization of motor control profiles in SCI when applying TSS as a therapeutic intervention for improving gait.

Reply to Daly, J.J. Comment on "Chow, J.W.; Stokic, D.S. Longitudinal Changes in Temporospatial Gait Characteristics during the First Year Post-Stroke. Brain Sci. 2021, 11, 1648".

This commentary [...].

Correction: Chow, J.W. and Stokic, D.S. Longitudinal Changes in Temporospatial Gait Characteristics during the First Year Post-Stroke. Brain Sci. 2021, 11, 1648.

The authors have made some changes in response to the reviewer's comments after the manuscript was published in December 2021 [...].

Longitudinal Changes in Temporospatial Gait Characteristics during the First Year Post-Stroke.

Given the paucity of longitudinal data in gait recovery after stroke, we compared temporospatial gait characteristics of stroke patients during subacute (<2 months post-onset, T0) and at approximately 6 and 12 months post-onset (T1 and T2, respectively) and explored the relationship between gait characteristics at T0 and the changes in gait speed from T0 to T1. Forty-six participants were assessed at T0 and a subsample of twenty-four participants were assessed at T2. Outcome measures included Fugl-Meyer lower-extremity motor score, 14 temporospatial gait parameters, and symmetry indices of 5 step parameters. Except for step width, all temporospatial parameters improved from T0 to T1 (p ≤ 0.0001). Additionally, significant improvements in symmetry were found for the initial double-support time and single-support time (p ≤ 0.0001). As a group, no significant differences were found between T1 and T2 in any of the temporospatial measures. However, the individual analysis revealed that 42% (10/24) of the subsample showed a significant increase in gait speed (Welch's t-test, p ≤ 0.002). Yet, only 5/24 (21%) of the participants improved speed from T1 to T2 according to speed-based minimum detectable change criteria. The increase in gait speed from T0 to T1 was negatively correlated with gait speed and stride length and positively correlated with the symmetry indices of stance and single-support times at T0 (p ≤ 0.002). Temporospatial gait parameters and stance time symmetry improved over the first 6 months after stroke with an apparent plateau thereafter. A greater increase in gait speed during the first 6 months post-stroke is associated with initially slower walking, shorter stride length, and more pronounced asymmetry in stance and single-support times. The improvement in lower-extremity motor function and bilateral improvements in step parameters collectively suggest that gait changes over the first 6 months after stroke are likely due to a combination of neurological recovery, compensatory strategies, and physical therapy received during that time.

Perception and predictors of health locus of control at rehabilitation discharge and 1 year after traumatic spinal cord injury.

This retrospective study examined the perception and predictors of health locus of control (LOC) in 71 individuals with a spinal cord injury (SCI) at discharge from inpatient rehabilitation (average age 39 years, 77% male, 54% black, 51% cervical SCI, 51% incomplete SCI and average time post-SCI 20 days). We also determined if health LOC beliefs and predictors change over the 1st year after SCI in a representative subsample of 36 individuals. The participants completed surveys regarding the health LOC, self-esteem and depression whereas demographic and SCI information were retrieved from medical records. At inpatient discharge, 55% of SCI individuals endorsed the doctor LOC category compared to internal (14%), other people (6%), chance (3%) or multiple LOC categories (22%). A similar pattern was found at 1-year postinjury (doctor LOC 44% and non-doctor LOC combined 56%). A backward stepwise regression revealed that white race (P = 0.093), >12 years of education (P = 0.001) and cervical level of SCI (P = 0.033) were significant predictors of the doctor LOC category at inpatient discharge (overall classification accuracy 76%). Similarly, >12 years of education (P = 0.055), cervical level of SCI at inpatient discharge (P = 0.033) and higher self-esteem at 1-year post-SCI (P = 0.113) were significant predictors of the doctor LOC category at 1-year post-SCI (overall classification accuracy 78%). We conclude that health LOC remains stable over the 1st year after SCI with the majority of individuals believing that the control over outcomes of their health is in the hands of doctors. These findings have implications for the provision of rehabilitation services after SCI.

Characteristics of rectus femoris activation and rectus femoris-hamstrings coactivation during force-matching isometric knee extension in subacute stroke.

The spectral properties of surface electromyographic (EMG) signal in the rectus femoris (RF) and the coactivation in the medial hamstrings (MH) were investigated in 45 stroke subjects (22 ± 12 days post-onset) and 30 age-matched healthy controls who performed unilateral knee extensions at maximum effort (100% MVC) and during 5-s force-matching tasks (10, 30, 50% MVC). The spectral properties were obtained through a power spectrum analysis based on Fast Fourier Transform. The coactivation was measured as the MH amplitude (%max) and MH/RF amplitude ratio. Force variability was expressed as the coefficient of variation. Both knee extensors and flexors were weaker in the paretic leg than the non-paretic and control legs (p < 0.001). A significantly higher relative power in the 5-13 and 13-30 Hz bands was found in the paretic than the non-paretic leg across all force levels (p ≤ 0.001) without changes in the 30-60 and 60-100 Hz bands or the mean and median frequencies. Regarding the antagonist coactivation, MH amplitude in the paretic leg was higher than in the non-paretic leg (submaximal levels, p < 0.0001) and the control leg (all force levels, p = 0.0005) with no differences between legs in the MH/RF ratio. The steadiness of the knee extension force was not related to the spectral properties of the agonist EMG or antagonistic coactivation. Greater coactivation was associated with weaker paretic knee flexors (p ≤ 0.0002). The overall results suggest variably altered agonist activation and antagonistic coactivation over the range of isometric knee extension contractions in subacute stroke.

Electrically induced cycling and nutritional counseling for counteracting obesity after spinal cord injury: A pilot study.

Objective: The purpose of this pilot study was to determine the preliminary efficacy of interval functional electrical stimulation (FES) cycling combined with nutritional counseling in obese adults with SCI.Setting: Community-based individuals with chronic SCI.Participants: Ten participants with chronic SCI.Interventions: Participants were divided into 2 groups (1) FES cycling and nutritional counseling (FES & Nutri) and (2) nutritional counseling only (Nutri Only). The FES & Nutri group performed high intensity interval FES cycling for 30 min 3 times per week for 8 weeks and received nutritional counseling for 30 min once per week for 8 weeks. The Nutri Only group received the nutritional counseling only.Outcome Measures: Body composition (fat mass, lean mass, body fat percentage), blood glucose levels.Results: Participants in the FES & Nutri group had a statistically significant greater decrease in body fat percentage (M = -1.14) compared to those in the Nutri Only group (M = +0.28) and gained more lean mass in their legs (M = +0.66 kg) compared to the Nutri Only group (M = -1.05 kg).Discussion/Conclusion: The statistically significant decrease in body fat percentage for the FES & Nutri group provides evidence that further study is merited. Future studies should include larger numbers of participants and the possible introduction of a preliminary strengthening program before initiating interval FES cycling. In addition, an increase in exercise volume and a greater role for nutritional counseling should be considered in order to optimize the treatment for obesity.

Safety and preliminary efficacy of functional electrical stimulation cycling in an individual with cervical cord injury, autonomic dysreflexia, and a pacemaker: Case report.

Context: Functional electric stimulation (FES) cycling is a commonly used therapeutic exercise modality after spinal cord injury (SCI); however, additional precautions must be taken in certain situations. The purpose of this study was to develop and apply a safety monitoring protocol for autonomic dysreflexia (AD) during FES cycling and to determine if an interval-FES cycling program can be safe and beneficial to an individual with cervical SCI, a history of AD, and a non-dependent cardiac pacemaker.The participant was a 36-year-old male with C6 AIS-C SCI sustained 9 years earlier, intermittent AD, and implanted cardiac pacemaker. Ten sessions of interval-FES cycling were performed twice weekly for 5 weeks. Rating of perceived exertion (RPE), blood pressure (BP), oxygen saturation (O2sat), and heart rate (HR) were monitored before, after, and every 5 min during cycling. ECG and cardiac pacemaker were evaluated by a cardiologist after ending the program.Findings: The participant reported self-limited chills 27 times over 10 sessions (19 "light", 3 "moderate", 5 "sharp"). Chills coincided with BP increases 59% of the time and their magnitudes moderately correlated (r = 0.32). The ECG was determined to be normal and the pacemaker fully functional at the end of the study, while blood glucose decreased (111-105 mg/dl), HbA1c levels increased (5.5-5.9%), and resting BP decreased (118/84-108/66 mmHg).Conclusion/Clinical Relevance: A person with cervical SCI, symptomatic AD, and a non-dependent pacemaker can safely participate and benefit from the interval-FES cycling program provided adequate monitoring of symptoms and vital signs.

Relations between knee and ankle muscle coactivation and temporospatial gait measures in patients without hypertonia early after stroke.

It is unclear whether muscle coactivation during gait is altered early after stroke and among which muscles. We sought to characterize muscle coactivation during gait in subacute stroke subjects without hypertonia and explore the relationship with temporospatial parameters. In 70 stroke (23 ± 12 days post-onset) and 29 age-matched healthy subjects, surface electromyography signals were used to calculate coactivation magnitude and duration between rectus femoris and medial hamstring (knee antagonistic coactivation), tibialis anterior and medial gastrocnemius (ankle antagonistic coactivation), and rectus femoris and medial gastrocnemius (extensor synergistic coactivation) during early double-support (DS1), early single-support (SS1), late single-support (SS2), late double-support (DS2), and swing (SW). Compared to both free and very-slow speeds of controls, stroke subjects had bilaterally decreased ankle coactivation magnitude in SS2 and duration in SS1 and SS2 as well as increased extensor coactivation magnitude in DS2 and SW. Both non-paretic knee and ankle coactivation magnitudes in SS2 moderately correlated with most temporospatial parameters (|r| ≥ 0.40). Antagonistic and synergistic coactivation patterns of the knee and ankle muscles during gait are altered bilaterally in subacute stroke subjects without lower limb hypertonia suggesting impairments in motor control. Greater coactivation magnitudes in the non-paretic knee and both ankles during the terminal stance (SS2) are associated with the overall worse gait performance. Unlike previously reported excessive coactivation or no change in chronic stroke, bilaterally decreased and increased coactivation patterns are present in subacute stroke. These findings warrant longitudinal studies to examine the evolution of changes in muscle coactivation from subacute to chronic stroke.

Bipolar transcutaneous spinal stimulation evokes short-latency reflex responses in human lower limbs alike standard unipolar electrode configuration.

Noninvasive electrical stimulation targeting the posterior lumbosacral roots has been applied recently in reflexes studies and as a neuromodulation intervention for modifying spinal cord circuitry after an injury. Here, we characterized short-latency responses evoked by four bipolar electrode configurations placed longitudinally over the spinal column at different vertebral levels from L1 to T9. They were compared with the responses evoked by the standard unipolar (aka monopolar) electrode configuration (cathode at T11/12, anode over the abdominal wall). Short-latency responses were recorded in the rectus femoris, medial hamstrings, tibialis anterior, and soleus muscles, bilaterally, in 11 neurologically intact participants. The response recruitment characteristics (maximal amplitude, motor threshold) and amplitude-matched onset latencies and paired-pulse suppression (35-ms interstimulus interval) were assessed with 1-ms current-controlled pulses at intensities up to 100 mA. The results showed that short-latency responses can be elicited with all bipolar electrode configurations. However, only with the cathode at T11/12 and the anode 10 cm cranially (∼T9), the maximum response amplitudes were statistical equivalent (P < 0.05) in the medial hamstrings, tibialis anterior, and soleus but not the rectus femoris, whereas motor thresholds were not significantly different across all muscles. The onset latency and paired-pulse suppression were also not significantly different across the tested electrode configurations, thereby confirming the reflex nature of the bipolar short-latency responses. We conclude that the bipolar configuration (cathode T11/12, anode ∼T9) produces reflex responses that are ostensibly similar to those evoked by the standard unipolar configuration. This provides an alternative approach for neuromodulation intervention.NEW & NOTEWORTHY Transcutaneous spinal stimulation with the identified bipolar electrode configuration may offer several advantages for neuromodulation interventions over commonly used unipolar configurations: there are no associated abdominal contractions, which improves the participant's comfort; additional dermatomes are not stimulated as when the anode is over the abdominal wall or iliac crest, which may have unwanted effects; and, due to a more localized electrical field, the bipolar configuration offers the possibility of targeting cord segments more selectively.

The utility of the single-subject method for comparison of temporal-spatial gait changes between a microprocessor and non-microprocessor prosthetic knees.

BACKGROUND: Despite increasing knowledge about the potential benefits of advanced user-controlled technology, the decision about switching an individual prosthesis user from a non-microprocessor prosthetic knee to a microprocessor prosthetic knee is mainly based on clinician's experience rather than empirical evidence. OBJECTIVES: To demonstrate the utility of single-subject design and data analysis for evaluating changes in temporal-spatial gait characteristics between walking with a non-microprocessor prosthetic knee and microprocessor prosthetic knee. STUDY DESIGN: Single-subject ABA/BAB design. METHODS: Seven non-microprocessor prosthetic knee users (all men, age 50-84 years, 3-40 years post-amputation) were transitioned through the ABA or BAB phases (A-NMPK, B-MPK, 5 weeks each). Four weekly gait evaluations were performed at three self-selected speeds with an electronic walkway. The non-microprocessor prosthetic knee-microprocessor prosthetic knee differences in stride length-cadence relationship, prosthetic weight acceptance, single-limb support, and step width were evaluated for each subject using the "non-overlap of all pairs" statistical method. RESULTS: Most subjects improved temporal-spatial gait while on the microprocessor prosthetic knee; in only one subject, none of the 10 gait parameters were in favor of the microprocessor prosthetic knee. In the BAB group, longer use of the microprocessor prosthetic knee was associated with shorter prosthetic weight acceptance and longer single-limb support times across three speeds. Step width either improved with the microprocessor prosthetic knee or remained unchanged in most subjects. CONCLUSION: The evidence of individual subject improvements in gait coordination, greater reliance on the prosthetic side, and better stability with the microprocessor prosthetic knee than non-microprocessor prosthetic knee over a range of walking speeds demonstrate the practical utility of the single-subject method in clinical decision-making. CLINICAL RELEVANCE: The results demonstrate the use of the single-subject method for examining person-specific differences in temporal-spatial gait characteristics between walking with a non-microprocessor prosthetic knee and microprocessor prosthetic knee at three self-selected speeds. The method proved feasible and reliable for documenting changes in gait at the individual level, which is relevant for clinical practice.

Knee Muscle Stretch Reflex Responses After an Intrathecal Baclofen Bolus in Neurological Patients With Moderate-to-Severe Hypertonia.

OBJECTIVES: To examine the prevalence, onset threshold, and response magnitude of stretch reflex response (SRR) in the knee extensors and flexors before and after an intrathecal baclofen (ITB) bolus injection in patients with moderate-to-severe hypertonia. MATERIALS AND METHODS: SRRs were elicited by reciprocal passive knee extension/flexion movements at preset angular velocities of 5, 60, 120, 180, 240, and 300°/s using an isokinetic dynamometer and recorded with surface electromyographic (EMG) electrodes placed over the knee extensors and flexors in 53 neurologic patients before and at 2.5 and 5 hours after an ITB injection via lumbar puncture. Outcome measures included the number of patients with presence/absence of SRRs, the number of SRRs per session, SRR onset threshold angle and velocity, and response magnitudes (peak EMG and area under the EMG curve) for each muscle. Pre-post comparisons were completed using the Fisher's exact and Wilcoxon signed rank tests. RESULTS: For both knee extensors and flexors, the proportion of patients with present SRRs (p < 0.0001) and the number of SRRs per session (p ≤ 0.027) decreased from pre- to post-ITB. The threshold velocity significantly increased post-injection in both muscles (p ≤ 0.001) without significant changes in the threshold angle. The response magnitudes significantly decreased in the knee extensors (p ≤ 0.016) but not the knee flexors after the injection. CONCLUSIONS: The prevalence and threshold velocity of SRR emerged as the most robust and practical parameters for assessing hyperreflexia during ITB bolus trial that can complement clinical assessment of muscle hypertonia.

Exteroceptive suppression of voluntary activity in thenar muscles by cutaneous stimulation: How many trials should be averaged?

OBJECTIVE: To determine a minimum number of trials that preserve input-output (I-O) properties of duration and magnitude of exteroceptive EMG suppression (eEMGs). PATIENTS AND METHODS: eEMGs was recorded in 16 healthy subjects from thenar muscles following index finger stimulation at 2.5, 5, 10, and 20 times sensory threshold (xST). Individual trials were rectified and incrementally averaged in blocks of 5, 10, 20, 30, 40, 50, and 60. To determine if the block size affects I-O properties, the goodness of curve fit parameter R2 for each block was compared to R2 of the global function across all blocks combined. RESULTS: eEMGs was found in all subjects at 10xST and 20xST (100%, respectively) but less often at 5xST (63-75%) and 2.5xST (25-56%). A quadratic function best described both duration and magnitude of eEMGs. The quadratic R2 did not significantly differ between any individual block function (5-60) and the global function (eEMGs duration 0.647-0.704 vs 0.679; magnitude 0.525-0.602 vs 0.560, respectively). CONCLUSIONS: Averaging 5 trials consistently shows eEMGs at and above 10xST. I-O properties of eEMGs do not differ whether 5 or up to 60 trials are averaged. Clinical studies of eEMGs in thenar muscles are possible with as few as 5 trials averaged.