Excitability of chronic hemiparetic muscles: determination of chronaxie values and strength-duration curves and its implication in functional electrical stimulation

Neuromuscular disorders in women and men with spinal cord injury are associated with changes in muscle and tendon architecture

OBJECTIVE

The present study aimed to determine the association between neuromuscular function, motor function impairment, and muscle and tendon structures in individuals with spinal cord injury (SCI) compared to a control (non-disabled) population.

DESIGN

A cross-sectional study with a control group.

SETTING

Center of Adapted Sports Training and Special Physical Education.

PARTICIPANTS

Fifteen individuals with SCI and motor function impairments participated in the study. A paired non-disabled group was recruited for comparison.

INTERVENTIONS

Not applicable.

OUTCOME MEASURES

Muscle (biceps brachii, rectus femoris, vastus lateralis, vastus medialis, and tibialis anterior) and tendon (quadriceps and patellar tendons) structures were assessed by ultrasound imaging (thickness, pennation angle, fascicle length, and echogenicity). Neuromuscular electrophysiological disorders were also assessed using electrodiagnosis techniques (stimulus non-responsivity and chronaxie) in the same muscles.

RESULTS

Except for the biceps brachii muscle, muscle thickness, pennation angle, and fascicle length were lower (p < 0.01) while echogenicity and chronaxie were greater (p < 0.01) in SCI participants. The SCI participants had a higher prevalence of neuromuscular electrophysiological disorders for all muscles, except the biceps brachii.

CONCLUSION

Neuromuscular disorders occur in association with muscle and tendon maladaptation in individuals with chronic SCI. A higher prevalence of electrophysiological disorders suggests an acquired polyneuromyopathy for muscles with motor function impairment even though the muscle was innerved, in addition to widespread muscle atrophy.

Strength-Duration Curves of Radial Nerve in Patients With Lateral Elbow Pain

CONTEXT

Lateral epicondylalgia (LE) refers to a painful condition at or around the lateral epicondyle of the humerus. LE is one of the most common injuries of the elbow; however, the cause of the pathology is not clear. Patients often experience symptoms consistent with a radial nerve injury; however, data on the involvement of the radial nerve are needed.

OBJECTIVE

To analyze the relationship between electrophysiologic excitability and morphology of the radial nerve in patients with unilateral chronic LE.

DESIGN

Cross-sectional study.

SETTING

Department of Physiotherapy, University of Seville.

PATIENTS

A total of 56 elbows (28 right, 28 left) in 28 patients (12 females, 16 males; age 49 [7.37] y) were recruited by convenience sampling.

MAIN OUTCOME MEASURES

Strength-duration curves (chronaxia and accommodation index) and cross-sectional area (CSA) of the radial nerve were made in all participants. All parameters were compared between both limbs. Also, pain with palpation in the lateral epicondyle and functional pain of involved extremities was assessed using visual analog scale and the Patient-Rated Tennis Elbow Evaluation, respectively.

RESULTS

Symptomatic limb showed higher CSA values of the radial nerve when compared with the asymptomatic limb (P < .001). On the symptomatic limb, duration of symptoms was positively correlated with CSA values. Chronaxia values were all normal and similar between both limbs (P = .35). Regarding accommodation index, 14 (54%) patients showed accommodation indices that suggested pathological radial nerve on the right limb, 4 (14%) on the left limb, 5 (18%) on both limbs, and 4 (14%) had none of the affected nerves. Eight-six percent of patients showed accommodation indices that suggested pathological radial nerve, independently of symptomatic limb. In these cases, affected nerves had higher CSA than the unaffected nerve (P = .01). On the affected nerves, duration of symptoms was positively correlated with accommodation indices.

CONCLUSIONS

These findings suggest that patients with unilateral chronic LE show a decreased excitability in any radial nerve, independently of the symptomatic limb, and that pathological nerves have higher CSA than the nonpathological nerves.

Intra and inter-raters reliability and agreement of stimulus electrodiagnostic tests with two different electrodes in sedated critically-ill patients

Objective: The aim of the present study was to verify the intra- and inter-rater reliability and agreement of the stimulus electrodiagnostic test (SET) measurements obtained by pen and square electrodes in the vastus lateralis and tibialis anterior muscles. Design: An intra- and inter-rater reliability and agreement study was performed for the SET by two independent raters. Two different sizes of cathode electrodes (1 cm² and 25 cm²) and two muscles were assessed (tibialis anterior and vastus lateralis). Results: Chronaxie did not change according to the different electrodes. A high intra-rater reliability (0.72 ≤ r ≤ 0.88) was detected independently of the electrode and muscle assessed. Moreover, moderate and almost perfect agreements (0.51 ≤ Kappa ≤ 1.00) were detected on intra-rater assessment. Similar correlations (0.74 ≤ r ≤ 0.79) were found for intra-rater reliability. However, dissimilar inter-rater agreement was detected: Kappa ≤ 0.40 for tibialis anterior and Kappa = 1.00 for vastus lateralis. Conclusion: The SET presented high reliability and moderate agreement in intra-rater evaluations. A fair agreement was found in the inter-rater assessment of the tibialis anterior. Evaluations performed with different electrode sizes did not influence the results. Therefore, the SET should be performed by a unique rater in test retest situations.

Neuromuscular electrophysiological disorders and muscle atrophy in mechanically-ventilated traumatic brain injury patients: New insights from a prospective observational study

PURPOSE

It is unclear whether the muscular changes in mechanically-ventilated traumatic brain injury patients (TBI) are only associated with disuse or additionally to neuromuscular electrophysiological disorders (NED). The correlation between muscle atrophy and NED may affect functional outcomes and rehabilitation programs significantly.

MATERIAL AND METHODS

An observational study was performed to investigate the presence of NED and muscle atrophy in TBI patients undergoing mechanical ventilation. NED was diagnosed by the stimulus electrodiagnosis test when chronaxie was ≥1000μs. The muscle structure (thickness and echogenicity) was assessed by B-mode ultrasound. Tibialis anterior (TA), rectus femoris (RF), and biceps brachialis (BB) muscles were analyzed. Patients were followed from the first day of admission in the intensive care unit (ICU) to the fourteenth day.

RESULTS

Twenty-two patients were analyzed. An increase of 48% in NED from day 1 to day 14 was detected in TA (p=0.004). All muscles presented a significant decrease in thickness (~18%, p<0.05), but echogenicity increased only in TA (19%), p<0.01 and RF (23%), p<0.01.

CONCLUSIONS

Mechanically-ventilated patients with TBI developed NED in addition to changes in muscle structure during their stay in the ICU.

A study on the operation of rehabilitation interfaces in active rehabilitation exercises for upper limb hemiplegic patients: Interfaces for lateral and bilateral exercises

BACKGROUND

For implementing autonomous rehabilitation exercises for upper limb hemiplegic patients, interfaces and a rehabilitation scenario that allow lateral and bilateral motions in a rehabilitation exercise robot are proposed.

OBJECTIVE

The proposed method measures the motion information generated from the unaffected part and projects it to an affected part in which the affected part expresses motions of the unaffected part.

METHODS

Both the accelerometer and gyro data were merged for estimating the motion information of the unaffected part. Also, HDR and complementary filters were applied to improve measurement errors in a data merging process.

RESULTS

For verifying the proposed method, a device, which is similar to a human body joint, was fabricated. Then, the angular values estimated by using an inertial sensor and the encoder values from the device were compared. In addition, a camera analysis was used to verify the proposed rehabilitation scenario by applying the rehabilitation interface proposed in this study to an exo-skeleton robot arm.

CONCLUSION

It is possible to apply the method proposed in this study to the control variables in different upper limb rehabilitation exercise robots. Thus, it is expected that patient centered active lateral/bilateral rehabilitation exercises can be performed through this interface method.

Strength-Duration Curves of the Common Fibular Nerve Show Hypoexcitability in People With Functional Ankle Instability

BACKGROUND

Some motor impairments, such as decreased reaction of peroneal muscles, altered kinematics, or poor postural control, have been described in people with functional ankle instability. Evidence shows a possible relationship between fibular nerve impairments and functional ankle instability.

OBJECTIVE

To investigate the electrophysiologic excitability of the common fibular nerve, as measured by strength-duration curves, in subjects with functional ankle instability compared with a control group without ankle impairment.

DESIGN

A cross-sectional study.

SETTING

University Research laboratory.

PARTICIPANTS

Fifty subjects with functional ankle instability (35 men, 15 women; ages 24.36 ± 5.01 years) and 63 uninjured control patients (44 men, 19 women; ages 22.67 ± 4.85 years) were recruited by convenience sampling.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Strength-duration curves of the common fibular nerve were made in all participants. Rheobase, chronaxie, Bawen index, accommodation index, galvano-tetanic threshold, and intensity thresholds for different pulse durations were obtained and compared between the 2 groups.

RESULTS

Subjects with functional ankle instability show increased values of chronaxie (0.58 ± 0.24 ms versus 0.47 ± 0.16 ms; P = .004), Bawen index (1.53 ± 0.24 versus 1.39 ± 0.21; P = .002), and intensity thresholds for pulse durations ≤2 ms both for rectangular and triangular pulse wave forms. The accommodation index was smaller in subjects with functional ankle instability than controls (3.7 ± 0.72 versus 4.05 ± 0.98; P = .036). The remaining parameters did not show significant differences between groups.

CONCLUSIONS

These findings suggest that subjects with functional ankle instability show a decreased excitability in their common fibular nerve when compared with subjects without ankle injuries.

A model for transcutaneous current stimulation: simulations and experiments

Complex nerve models have been developed for describing the generation of action potentials in humans. Such nerve models have primarily been used to model implantable electrical stimulation systems, where the stimulation electrodes are close to the nerve (near-field). To address if these nerve models can also be used to model transcutaneous electrical stimulation (TES) (far-field), we have developed a TES model that comprises a volume conductor and different previously published non-linear nerve models. The volume conductor models the resistive and capacitive properties of electrodes, electrode-skin interface, skin, fat, muscle, and bone. The non-linear nerve models were used to conclude from the potential field within the volume conductor on nerve activation. A comparison of simulated and experimentally measured chronaxie values (a measure for the excitability of nerves) and muscle twitch forces on human volunteers allowed us to conclude that some of the published nerve models can be used in TES models. The presented TES model provides a first step to more extensive model implementations for TES in which e.g., multi-array electrode configurations can be tested.