Voluntary Motor Unit Recruitment Research Articles

Efficacy analysis of ansa cervicalis anterior root-recurrent laryngeal nerve anastomosis in the treatment of unilateral vocal cord paralysis

Objective:Investigates the application and clinical efficacy of ansa cervicalis anterior root-recurrent laryngeal nerve（RLN） anastomosis in the treatment of unilateral vocal fold paralysis（UVFP）. Methods:A prospective study was conducted with 92 UVFP patients admitted to our department from January 2018 to January 2022 who received ansa cervicalis anterior root-RLN anastomosis. The course of nerve injury ranged from 6 to 24 months. Videostroboscopy, voice subjective auditory perceptual assessment（GRBAS）, Voice Handicap Index（VHI-10）, voice objective acoustic analysis and laryngeal electromyography（EMG） were used to evaluate the efficacy of the operation. Results:Videostroboscopy showed that although the movement of vocal cords did not return to normal 12 months after operation, their volume and muscle tension were significantly improved and their positions were adducted to the median or near-median. Also the glottic closure, vocal cord position, vocal cord edge, symmetry and regularity of vocal cord vibration were significantly improved than pre-operation（P<0.01）. The five indexes of GRBAS（Grade, Roughness, Breathiness, Asthenia, Strain） and VHI-10, as well as voice acoustic parameters（Jitter, Shimmer, NHR） post-operation were significantly reduced, while the maximum phonation time（MPT） was significantly longer（P<0.01）. The results of laryngeal EMG indicated that the maximum voluntary motor unit recruitment（VMUR） post-operation was significantly recovered（P<0.01）, which confirmed that the affected laryngeal muscle obtained effective nerve reinnervation. Conclusion:Ansa cervicalis anterior root-RLN anastomosis can effectively improve the voice function of patients which is safe and satisfactory. It is an ideal method for the treatment of unilateral RLN injury.

Prognostic value of needle electromyography in traumatic brachial plexus injury.

In this study we aimed to determine whether needle electromyographic assessment of voluntary motor unit recruitment in traumatic brachial plexus injuries could predict spontaneous motor recovery. A retrospective study was performed on patients with brachial plexus injury affecting deltoid, supraspinatus/infraspinatus, and biceps brachii. The outcome measure was strength on manual muscle testing at least 1 year after injury. Good outcome was considered strength >3/5 on the Medical Research Council (MRC) scale. No muscles with no recruitment (n = 27) at 1-9 months improved to MRC 4/5 strength at a mean of 2.0 years postinjury. Twenty-five percent of muscles with discrete or severely reduced recruitment (n = 8) regained strength to >3/5 at a mean of 1.4 years postinjury (P = .047). Absent voluntary motor unit potential recruitment at 1-9 months predicted poor prognosis for spontaneous recovery. A high percentage of patients with discrete recruitment did not improve to >3/5 strength. These patients should be considered for early nerve transfer surgery.

The effect of patient age on the success of laryngeal reinnervation.

The objective of the study was to investigate the influence of patient age on the efficacy of laryngeal reinnervation with ansa cervicalis in unilateral vocal fold paralysis (UVFP) patients. We retrospectively reviewed 349 consecutive UVFP cases of laryngeal reinnervation with ansa cervicalis to the recurrent laryngeal nerve anastomosis. Preoperative and postoperative videostroboscopy, perceptual evaluation, acoustic analysis, maximum phonation time (MPT) and laryngeal electromyography (EMG) data were collected. Gender, age, preoperative EMG status [preoperative voluntary motor unit recruitment (VMUR)] and denervation duration were analyzed in previous multivariable logistic regression analysis. Stratification analysis was performed on patient age in the present study. All patients were divided into four groups according to their age: Group A included patients with an age less than 30 years; Group B, 30-44 years; Group C, 45-59 years; Group D, ≥60 years. Stratification analysis on patient age showed significant differences between Group A and D, Group B and D, Group C and D (P < 0.05), but no significant difference between Group A and B, Group A and C, Group B and C (P > 0.05), respectively, with regard to parameters including glottal closure, overall grade, shimmer, noise-to-harmonics ratio; but there are no significant differences among the four groups with regard to jitter. However, for MPT and postoperative VMUR, there are significant differences among the four groups expect between Group A and B. In addition, glottal closure, perceptual and acoustic parameters, MPT values and VMUR data, were significantly improved postoperatively in each age group (P < 0.01). The data from this study indicate that patient age is an influential factor of the surgical outcome of laryngeal reinnervation for UVFP patients. Laryngeal reinnervation is less effective when patient age is more than 60 years.

Bridging Gaps Between the Recurrent Laryngeal Nerve and Ansa Cervicalis Using Autologous Nerve Grafts

We investigated the clinical efficacy of free nerve grafts in bridging gaps between the recurrent laryngeal nerve (RLN) and ansa cervicalis in patients with unilateral RLN injury. We retrospectively reviewed the charts of 14 patients who underwent relevant free nerve grafting and assessed the clinical outcomes of this procedure. Between January 2000 and January 2010, 14 patients with unilateral vocal fold paralysis were enrolled in this study. In all patients, the RLN was resected and free nerve grafts were applied to bridge the gap between the distal stump of the RLN and the anterior root of ansa cervicalis during surgery. Videostroboscopy, acoustic analysis, perceptual evaluation, maximum phonation time (MPT), and laryngeal electromyography (EMG) were performed both preoperatively and postoperatively to assess the clinical outcomes. Videostroboscopic findings showed that glottic closure, vocal fold edge, vocal fold position, phase symmetry, and phase regularity were significantly improved postoperatively (P<0.05), and no paradoxical movements of vocal folds were observed. Perceptual evaluation showed that overall grade, roughness, breathiness, asthenia, and strain were also significantly decreased postoperatively (P<0.05). The acoustic parameters jitter (local) and shimmer (local) and the mean noise-to-harmonics ratio were significantly lower than the corresponding preoperative values (P<0.05). The postoperative MPT values were also significantly longer than the preoperative values. Laryngeal EMG revealed significant improvement in voluntary motor unit recruitment during phonation postoperatively (P<0.05). Free nerve grafting is an effective procedure in bridging the gap between the RLN and ansa cervicalis in patients with unilateral RLN injury, as well as a safe procedure without obvious morbidity. A satisfactory vocal outcome can be obtained.

Contralateral ansa cervicalis‐to‐recurrent laryngeal nerve anastomosis for unilateral vocal fold paralysis: A long‐term outcome analysis of 56 cases

To evaluate the long-term efficacy of contralateral ansa cervicalis-to-recurrent laryngeal nerve (RLN) anastomosis for unilateral vocal fold paralysis (UVFP), when the ansa cervicalis on the side of the paralyzed vocal fold was absent or there was any question about its viability. We retrospectively reviewed 56 consecutive cases of delayed laryngeal reinnervation with contralateral ansa cervicalis for UVFP. Between January 1996 and January 2008, a total of 56 UVFP patients were enrolled in this study. All patients underwent contralateral ansa cervicalis-to-RLN anastomosis. Videostroboscopy, acoustic analysis, perceptual evaluation and maximum phonation time (MPT), and laryngeal electromyography (LEMG) were performed pre- and postoperatively. Analysis of videostroboscopic findings indicated that the glottic closure, vocal fold edge, vocal fold position, phase symmetry, and regularity were significantly improved (P < .001, post- vs. preoperative). Perceptual evaluation of dysphonia severity showed that overall grade, roughness, breathiness, asthenia, and strain were also significantly decreased postoperatively (P < .001). Postoperative values of jitter (local), shimmer (local), and mean noise-to-harmonics ratio were significantly lower than the corresponding preoperative values (P < .001). The postoperative MPT value was significantly longer than the preoperative one (P < .001). LEMG showed that there was a significant postoperative improvement in voluntary motor-unit recruitment during phonation (P < .001). In cases with a lack of viable ansa cervicalis on the side of a paralyzed vocal fold, contralateral ansa cervicalis-to-RLN anastomosis is a feasible and effective approach in the treatment of UVFP and can restore physiologic laryngeal phonatory function.

Electromyographic laryngeal synkinesis alters prognosis in vocal fold paralysis

Synkinesis, or misdirected reinnervation, is likely a confounder when predicting return of function of an immobile vocal fold. Currently, no information exists on the incidence of synkinesis in unilateral vocal fold immobility (UVFI) or the effect synkinesis has on prognosis and treatment. Our objective was to examine a vocal fold adductor synkinesis screening protocol using diagnostic laryngeal electromyography (LEMG). We aim to determine the effect of synkinesis on prognosis of recovery of purposeful vocal fold motion. Retrospective review of LEMG data and patient charts from laryngology practice. A standardized LEMG analysis method to diagnose vocal fold adductory synkinesis was performed in 124 consecutive laryngeal electromyographic exams. Synkinesis testing was positive in 12/124 patients (9.7%). Post hoc quantitative analysis of electromyographic recordings to compare motor unit potential amplitude in the thyroarytenoid/lateral cricoarytenoid complex during sustained phonation to those in the same muscle during a "sniff" revealed a significant difference in motor unit potential amplitude ratio for control subjects (0.32), those who recovered purposeful vocal fold motion (0.40), and those with vocal fold paralysis (0.96) (P = .001). The presence of synkinesis in patients with UVFI improved the negative predictive value of LEMG from 53% to 100% and the sensitivity from 56% to 100%. Presence of laryngeal synkinesis using motor amplitude ratio criteria, in the setting of good voluntary motor unit recruitment and UVFI, downgrades a patient's prognosis to one that is poor for recovery. We propose this screening protocol as an adjunct to diagnostic LEMG.

Decreased capillarization and a shift to fast myosin heavy chain IIx in the biceps brachii muscle from young adults with spastic paresis

Muscle spasticity and paresis are conditions that occur secondary to upper motor neuron lesions. The co-existence of decreased motor unit recruitment and intermittent over-activity generates confusion concerning the effect on muscle fiber characteristics. In order to increase the knowledge about the effect of upper motor lesion on capillarization and muscle fiber composition, the biceps brachii muscle from seven young adults with long duration of spastic paresis and seven age-matched controls were analyzed using morphological and enzyme- and immuno-histochemical techniques. The spastic muscles had a 38% lower capillary density ( p = 0.002), 30% fewer capillaries around each muscle fiber ( p = 0.02), and 16% fewer capillaries when related to the fiber size ( p = 0.04). The frequency of fibers expressing myosin heavy chain (MyHC) IIx increased (30% vs. 4%, p = 0.006), while the percentage of fibers expressing MyHC I and MyHC IIa, respectively, decreased (22% vs. 46% and 7% vs. 29%, p < 0.01). The high proportion of muscle fibers with low oxidative capacity and low capillary supply indicates that biceps brachii muscle from patients with upper motor lesions fatigue more easily than normal controls. We also observed a significantly higher variability in fiber size for fibers expressing MyHC I ( p < 0.04), and, in three of the subjects, a small amount of small fibers expressing developmental MyHCs was found. These results suggest that, although intermittent stretch reflex contractions might have an impact on the muscle characteristics in spastic paresis, the muscle phenotypic properties are more adapted to decreased voluntary motor unit recruitment.

Pathophysiology of spastic paresis. I: Paresis and soft tissue changes

Spastic paresis follows chronic disruption of the central execution of volitional command. Motor function in patients with spastic paresis is subjected over time to three fundamental insults, of which the last two are avoidable: (1) the neural insult itself, which causes paresis, i.e., reduced voluntary motor unit recruitment; (2) the relative immobilization of the paretic body part, commonly imposed by the current care environment, which causes adaptive shortening of the muscles left in a shortened position and joint contracture; and (3) the chronic disuse of the paretic body part, which is typically self-imposed in most patients. Chronic disuse causes plastic rearrangements in the higher centers that further reduce the ability to voluntarily recruit motor units, i.e., that aggravate baseline paresis. Part I of this review focuses on the pathophysiology of the first two factors causing motor impairment in spastic paresis: the vicious cycle of paresis-disuse-paresis and the contracture in soft tissues.

Force-frequency relationship and potentiation in mammalian skeletal muscle.

Repetitive activation of a skeletal muscle results in potentiation of the twitch contractile response. Incompletely fused tetanic contractions similar to those evoked by voluntary activation may also be potentiated by prior activity. We aimed to investigate the role of stimulation frequency on the enhancement of unfused isometric contractions in rat medial gastrocnemius muscles in situ. Muscles set at optimal length were stimulated via the sciatic nerve with 50-micros duration supramaximal pulses. Trials consisted of 8 s of repetitive trains [5 pulses (quintuplets) 2 times per second or 2 pulses (doublets) 5 times per second] at 20, 40, 50, 60, 70, and 80 Hz. These stimulation frequencies represent a range over which voluntary activation would be expected to occur. When the frequency of stimulation was 20, 50, or 70 Hz, the peak active force (highest tension during a contraction - rest tension) of doublet contractions increased from 2.2 +/- 0.2, 4.1 +/- 0.4, and 4.3 +/- 0.5 to 3.1 +/- 0.3, 5.6 +/- 0.4, and 6.1 +/- 0.7 N, respectively. Corresponding measurements for quintuplet contractions increased from 2.2 +/- 0.2, 6.1 +/- 0.5, and 8.7 +/- 0.7 to 3.2 +/- 0.3, 7.3 +/- 0.6, and 9.0 +/- 0.7 N, respectively. Initial peak active force values were 27 +/- 1 and 61.5 +/- 5% of the maximal (tetanic) force for doublet and quintuplet contractions, respectively, at 80 Hz. With doublets, peak active force increased at all stimulation frequencies. With quintuplets, peak active force increased significantly for frequencies up to 60 Hz. Twitch enhancement at the end of the 8 s of repetitive stimulation was the same regardless of the pattern of stimulation during the 8 s, and twitch peak active force returned to prestimulation values by 5 min. These experiments confirm that activity-dependent potentiation is evident during repeated, incompletely fused tetanic contractions over a broad range of frequencies. This observation suggests that, during voluntary motor unit recruitment, derecruitment or decreased firing frequency would be necessary to achieve a fixed (submaximal) target force during repeated isometric contractions over this time period.