The vestibulo-collic reflex

Until now there has no been no simple, reliable clinical test that assesses the function of the otolith organs. However, recent work has suggested the occurrence of an easily identifiable electromyographic (EMG) waveform in isometrically contracting sternomastoid muscles in response to loud clicks. This is thought to represent an otolith evoked disynaptic reflex. Equipment routinely used for evoked response audiometry (ERA) has been adapted to investigate this response. A short latency (8 ms) positive-negative EMG waveform has been recorded in 31 of 32 normal subjects. The latency of the positive peak (P1) is 11.7 ms ( sd = 0.89), and the negative peak (N1) is 20.5 ms ( sd = 1.89). It is predominantly ipsilateral, although a contralateral response was present in 35.5%. The response has also been recorded in three patients with a severe unilateral sensorineural hearing loss and normal caloric responses, and in a patient undergoing cochlear implantation for profound bilateral sensorineural hearing loss. Further work is required to delineate the value of this technique in investigating vestibular lesions.     

性激素水平对年轻女性颏舌肌肌电活性的影响

目的初步探讨性激素水平对颏舌肌肌电活性的影响。方法借助多导睡眠仪和肌电仪对10名正常年轻女性分别在卵泡期和黄体期清醒及睡眠状态下的颏舌肌肌电活性进行监测,分析两个性周期之间受睡眠影响颏舌肌肌电活性下降程度的差异。结果无论是在女性月经周期的卵泡期还是黄体期,睡眠非快速动眼期(non-rap ideye movem ent,NREM)的颏舌肌活性均显著低于清醒期(卵泡期P=0.000 3,黄体期P=0.000 5)。黄体期颏舌肌受睡眠影响其肌电活性下降程度低于卵泡期(P=0.036 6)。结论初步研究表明,女性激素水平与颏舌肌肌电活性有关。     

表面肌电图在儿童吞咽障碍疾病中的应用

目的 探讨表面肌电图在儿童吞咽障碍疾病中的应用价值。方法 选取吞咽障碍患儿20例为观察组,招募性别及年龄相匹配的健康儿童20例为对照组。采用表面肌电图记录两组儿童静息状态及吞水状态颏下肌群和舌骨下肌群肌电积分值。比较两组儿童静息状态下及吞水5 mL后颏下肌群和舌骨下肌群肌电积分值的差异。记录观察组患儿康复治疗1个月后颏下肌群和舌骨下肌群肌电积分值的变化。采用Spearman相关分析法评估观察组患儿吞咽障碍程度与颏下肌群及舌骨下肌群肌电积分值的相关性。结果 静息状态下两组儿童颏下肌群和舌骨下肌群肌电积分差异无统计学意义（P > 0.05）,但在吞水后观察组的肌电积分值明显高于对照组（P < 0.05）。治疗后观察组吞咽障碍临床症状改善,颏下肌群和舌骨下肌群肌电积分值较前明显降低（P < 0.05）。吞咽障碍严重程度与颏下肌群和舌骨下肌群肌电积分值呈正相关（P < 0.01）。结论 表面肌电图检查可以作为儿童吞咽障碍诊断及疗效评估的方法之一。     

A pilot study of nocturnal temporalis muscle activity in TMD diagnostic groups of women

Temporomandibular disorder (TMD) incidences are believed to be related to parafunctional behaviours like teeth clenching. This pilot study aimed to (i) develop an automated clench‐detection algorithm, and (ii) apply the algorithm to test for differences in nocturnal clenching in women with and without TMD. Subjects gave informed consent to participate. Adult women were categorised using Diagnostic Criteria for TMD according to presence/absence (+/?) of both TM joint disc placement (DD) and chronic pain (P) into two groups (+DD+P, ?DD?P) with 12 subjects each. Surface temporalis electromyography was recorded during oral tasks performed by subjects at two laboratory sessions. The data were used to characterise muscle activity per N of bite force (μV/N) for each subject, develop the clench‐detection algorithm and test its accuracy. Ambulatory surface temporalis electromyography was self‐recorded by each subject over three nights and analysed using the algorithm and bite force (N) versus muscle activity μV/N calibrations. Bonferroni‐adjusted homoscedastic t‐tests assessed for significant between‐group differences in clenching (P < 0·05). Sensitivity, specificity and accuracy of algorithm‐detected laboratory clenches were all ≥96%. During self‐recordings 95% of clenches had durations of <4 s and peak forces of <10 N in both groups. Mean clench durations were significantly longer (P = 0·042) in +DD+P (1·9 ± 0·8 s) than ?DD?P subjects (1·4 ± 0·4 s). Mean temporalis duty factors (%clench time/total recording time) were significantly larger (P = 0·041) in +DD+P (0·47 ± 0·34%) than ?DD?P (0·26 ±0·22%) subjects. Nocturnal temporalis muscle activities detected by a validated algorithm were longer per clench and recording time in +DD+P compared to ?DD?P women.     

Effects of experimental occlusal interference on body posture: an optoelectronic stereophotogrammetric analysis

In recent years, there has been increasing interest in the relationship between dental occlusion and body posture both among people and in scientific literature. The aim of the present longitudinal study is to investigate the effects of an experimental occlusal interference on body posture by means of a force platform and an optoelectronic stereophotogrammetric analysis. An occlusal interference of a 0‐ to 2‐mm‐thick glass composite was prepared to disturb the intercuspal position while not creating interference during lateral or protrusive mandibular excursions. Frontal and sagittal kinematic parameters, dynamic gait measurements and superficial electromyographic (SEMG) activity of head and neck muscles were performed on 12 healthy subjects. Measurements were taken 10 days before the application of the occlusal interference, and then immediately before the application, the day after it, and at a distance of 7 and 14 days under four different exteroceptive conditions. The outcomes of this study show that an occlusal interference does not modify significantly over time static and dynamic parameters of body posture under different exteroceptive conditions. It has a minimal influence only on the frontal kinematic parameters related to mandibular position, and it induces a transient increase of the activity of masticatory muscles. In this study, the experimental occlusal interference did not significantly influence the body posture during a 14‐day follow‐up period.     

Intraoperative lateral rectus electromyographic recordings optimized by deep intraorbital needle electrodes

ObjectiveWe demonstrate the advantages and safety of long, intraorbitally-placed needle electrodes, compared to standard-length subdermal electrodes, when recording lateral rectus electromyography (EMG) during intracranial surgeries.MethodsInsulated 25 mm and uninsulated 13 mm needle electrodes, aimed at the lateral rectus muscle, were placed in parallel during 10 intracranial surgeries, examining spontaneous and stimulation-induced EMG activities. Postoperative complications in these patients were reviewed, alongside additional patients who underwent long electrode placement in the lateral rectus.ResultsIn 40 stimulation-induced recordings from 10 patients, the 25 mm electrodes recorded 6- to 26-fold greater amplitude EMG waveforms than the 13 mm electrodes. The 13 mm electrodes detected greater unwanted volume conduction upon facial nerve stimulation, typically exceeding the amplitude of abducens nerve stimulation. Except for one case with lateral canthus ecchymosis, no clinical or radiographic complications occurred in 36 patients (41 lateral rectus muscles) following needle placement.ConclusionsIntramuscular recordings from long electrode in the lateral rectus offers more reliable EMG monitoring than 13 mm needles, with excellent discrimination between abducens and facial nerve stimulations, and without significant complications from needle placement.SignificanceLong intramuscular electrode within the orbit for lateral rectus EMG recording is practical and reliable for abducens nerve monitoring.     

New method of neck surface electromyography for the evaluation of tongue‐lifting activity

Elevation of the posterior part of the tongue is important for normal deglutition and speech. The purpose of this study was to develop a new surface electromyography (EMG) method to non‐invasively and objectively evaluate activity in the muscles that control lifting movement in the posterior tongue. Neck surface EMG (N‐EMG) was recorded using differential surface electrodes placed on the neck, 1 cm posterior to the posterior border of the mylohyoid muscle on a line orthogonal to the lower border of the mandible. Experiment 1: Three healthy volunteers (three men, mean age 37·7 years) participated in an evaluation of detection method of the posterior tongue lifting up movement. EMG recordings from the masseter, temporalis and submental muscles and N‐EMG revealed that i) N‐EMG was not affected by masseter muscle EMG and ii) N‐EMG activity was not observed during simple jaw opening and tongue protrusion, revealing the functional difference between submental surface EMG and N‐EMG. Experiment 2: Seven healthy volunteers (six men and one woman, mean age 27·9 years) participated in a quantitative evaluation of muscle activity. Tongue‐lifting tasks were perfor‐med, exerting a prescribed force of 20, 50, 100 and 150 gf with visual feedback. For all subjects, a significant linear relationship was observed bet‐ween the tongue‐lifting force and N‐EMG activity (P < 0·01). These findings indicate that N‐EMG can be used to quantify the force of posterior tongue lifting and could be useful to evaluate the effect of tongue rehabilitation in future studies.     

Influence of sustained submaximal clenching fatigue test on electromyographic activity and maximum voluntary bite forces in healthy subjects and patients with temporomandibular disorders

This study aimed to investigate whether the fatigue induced by sustained motor task in the jaw elevator muscles differed between healthy subjects and patients with temporomandibular disorder (TMD). Fifteen patients with TMD and thirteen age‐ and sex‐matched healthy controls performed a fatigue test consisting of sustained clenching contractions at 30% maximal voluntary clenching intensity until test failure (the criterion for terminating the fatigue test was when the biting force decreased by 10% or more from the target force consecutively for >3 s). The pre‐ and post‐maximal bite forces (MBFs) were measured. Surface electromyographic signals were recorded from the superficial masseter muscles and anterior temporal muscles bilaterally, and the median frequency at the beginning, middle and end of the fatigue test was calculated. The duration of the fatigue test was also quantified. Both pre‐ and post‐MBFs were lower in patients with TMD than in controls (P < 0·01). No significant difference was found in the percentage change in MBF between groups. The duration of the fatigue test in TMD patients was significantly shorter than that of the controls (P < 0·05). Our results suggest that, compared to healthy subjects, patients with TMD become more easily fatigued, but the electromyographic activation process during the fatigue test is similar between healthy subjects and patients with TMD. However, the mechanisms involved in this process remain unclear, and further research is warranted.     

Effect of experimental jaw muscle pain on EMG activity and bite force distribution at different level of clenching

Bite force at different levels of clenching and the corresponding electromyographic (EMG) activity in jaw‐closing muscles were recorded in 16 healthy women before, during and after painful stimulation of the left masseter muscle. Experimental pain was induced by infusion of 5·8% hypertonic saline (HS), and 0·9% isotonic saline (IS) was infused as a control. EMG activity was recorded bilaterally from the masseter and temporalis muscles, and static bite force was assessed by pressure‐sensitive films (Dental Pre‐scale) at 5, 50 and 100% of maximal voluntary contraction (MVC) during each session. Visual feedback was applied by showing EMG activity to help the subject perform clenching at 5, 50 and 100% MVC, respectively. EMG activity at 100% MVC in left and right masseter decreased significantly during painful HS infusion (1·7–44·6%; P < 0·05). EMG activity at 5% and 50% MVC was decreased during HS infusion in the painful masseter muscle (4·8–18·6%; P < 0·05); however, EMG activity in the other muscles increased significantly (18·5–128·3%; P < 0·05). There was a significant increase in bite force in the molar regions at 50% MVC during HS infusion and in the post‐infusion condition (P < 0·05). However, there were no significant differences in the distribution of forces at 100% MVC. In conclusion, experimental pain in the masseter muscle has an inhibitory effect on jaw muscle activity at maximal voluntary contraction, and compensatory mechanisms may influence the recruitment pattern at submaximal efforts.