Quantitative surface EMG of pericranial muscles. Relation to age and sex in a general population

Standardization of facial electromyographic responses

In behavioral studies, facial electromyographic (EMG) responses to external stimuli or internal events are usually quantified relative to the resting state, presumed to represent a neutral baseline condition. In the large majority of recent studies, EMG responses were expressed as a difference score in terms of microvolts with the resting state. We argue that since EMG activity is measured on a ratio scale rather than on an interval scale, percentage scores should be used instead of difference scores. Reanalyzing results from an earlier study on the relationships between facial EMG responses and affective empathic responses to emotional video clips, we found that the two different types of EMG response quantification were differently related to affective empathy. Relationships between EMG responses and affective empathy were more consistent or stronger for percentage scores than for difference scores. In another study, facial EMG mimicry responses to pictures of emotional facial expressions were stronger for percentage scores than for difference scores. The adequacy of percentage scores relative to difference scores as indices of psychological variables may be simply checked by comparing both types of scores.

Relationship between demographic and cephalometric measures and electromyographic activityu of the facial musculature. A preliminary study in children and adolescents

Surface electromyography (EMGS) is used to evaluate the electromyographic activity of the orofacial musculature at rest, or when performing certain activities such as swallowing saliva or water, or tasks of maximum voluntary contraction. Numerous studies have evaluated the relationship between facial morphology and muscle activity, with contradictory results. The aim of this study was to determine whether there are significant differences in the electromyographic activity of the orofacial musculature as a function of the variables: age, height, weight, facial pattern and skeletal class. For this purpose, 81 patients with dental malocclusion were selected (35 males and 46 females, aged 6 to 17 years). Bilateral EMGS activity of the temporalis, masseter, orbicularis oris of the upper and lower lip of the mouth and suprahyoid muscles was measured in the resting position, maximum voluntary contraction and swallowing of saliva 2 ml of water. The results obtained show that the mandibular plane and the ANB angle present significant differences in all the variables of EMGS activity; however, the facial pattern only shows significant differences in the mean deviation of muscle activity. Skeletal class shows no significant effect on any of the EMGS variables recorded. The variables Age, Weight and Height show significant results on all EMGS activity variables. The variable Sex only shows significant results in the mean deviation of muscle activity. This work supports previous studies that found no significant results based on facial pattern and skeletal class. It would be advisable to perform a more exhaustive analysis of the muscles involved and their relationship between the different tasks evaluated, and to increase the sample size of patients with skeletal Class III in order to reach more definitive conclusions.

Interference of tonic muscle activity on the EEG: a single motor unit study

The electrical activity of muscles can interfere with the electroencephalogram (EEG) signal considering the anatomical locations of facial or masticatory muscles surrounding the skull. In this study, we evaluated the possible interference of the resting activity of the temporalis muscle on the EEG under conventional EEG recording conditions. In 9 healthy adults EEG activity from 19 scalp locations and single motor unit (SMU) activity from anterior temporalis muscle were recorded in three relaxed conditions; eyes open, eyes closed, jaw dropped. The EEG signal was spike triggered averaged (STA) using the action potentials of SMUs as triggers to evaluate their reflections at various EEG recording sites. Resting temporalis SMU activity generated prominent reflections with different amplitudes, reaching maxima in the proximity of the recorded SMU. Interference was also notable at the scalp sites that are relatively far from the recorded SMU and even at the contralateral locations. Considering the great number of SMUs in the head and neck muscles, prominent contamination from the activity of only a single MU should indicate the susceptibility of EEG to muscle activity artifacts even under the rest conditions. This study emphasizes the need for efficient artifact evaluation methods which can handle muscle interferences.

Stretch Reflex and Pressure Pain Thresholds in Chronic Tension-Type Headache Patients and Healthy Controls

To compare the jaw-stretch reflex and pressure pain thresholds (PPT) in chronic tension-type headache (CTTH) patients and healthy controls, 30 patients (15 male and 15 female) and 30 age- and sex-matched healthy subjects were investigated. Stretch reflexes were recorded in the temporalis and masseter muscles and PPT was determined in the anterior temporalis, splenius capitis and masseter muscles. The results showed that the amplitude of the stretch reflex in CTTH patients was higher compared with control subjects ( P < 0.045), and higher in women compared with men in the right and left anterior temporalis muscles ( P < 0.009). There were no differences in the PPT value between CTTH and control subjects ( P > 0.509), whereas women showed significantly lower PPT measurements ( P < 0.046). The results demonstrated a facilitation of the stretch reflex pathways in CTTH patients that is unrelated to measures of pericranial sensitivity.

The clinical usefulness of surface electromyography in the diagnosis and treatment of temporomandibular disorders

BACKGROUND

This article presents a comprehensive review of the recent literature regarding the scientific support for the use of surface electromyography (SEMG) in diagnosing and treating temporomandibular disorders (TMDs).

TYPES OF STUDIES REVIEWED

The authors conducted a Medline search involving human studies using the key words "surface electromyography or electromyography" and "masticatory muscles or temporomandibular disorders or craniomandibular disorders." They also reviewed relevant articles regarding the clinical usefulness of SEMG based on reliability, validity, sensitivity and specificity, as well as additional references included in some of the articles.

RESULTS

The clinical use of SEMG in the diagnosis and treatment of TMD is of limited value when one considers reliability, validity, sensitivity and specificity as measurement standards. SEMG does not appear to contribute any additional information beyond what can be obtained from the patient history, clinical examination and, if needed, appropriate imaging.

CONCLUSIONS

Clinically, the determination of the presence or absence of TMD does not appear to be enhanced by the use of SEMG. However, the modality may be useful in a meticulously controlled research setting.

CLINICAL IMPLICATIONS

SEMG has limited value in the detection or management of TMD and in some instances may lead to unnecessary dental therapy as a solution for those disorders.

Influence of age and gender on the jaw-stretch and blink reflexes

The aim of this study is to investigate the influence of age and gender on jaw-stretch and blink reflexes (BR). Thirty "young" (26.5+/-0.7 years) and thirty "old" (47.8+/-1.8 years) healthy adults were included. Short-latency stretch reflex responses were evoked in the masseter and temporalis muscles by fast jaw-stretches, and BR in orbicularis oculi muscle were evoked by painful electrical pulses (0.5 ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen. For the jaw-stretch reflex, the pre-stimulus EMG activity in the old subjects was significantly lower than that of the young subjects in the right and left masseter and temporalis muscles (P<0.006), whereas there was no difference in the results between males and females. The normalized peak-to-peak amplitude of the EMG in the left masseter and left and right temporalis muscles was significantly lower in the old subjects compared with the young subjects (P<0.02). Females had significantly higher normalized peak-to-peak EMG amplitudes compared with males in the right masseter and left temporalis muscles (P<0.05). The old subjects had significantly lower root mean square (RMS) (P=0.01) and average (P<0.02) BR values in the right and left orbicularis oculi muscles, and lower area under the curve (AUC) (P=0.02) values in the left orbicularis oculi muscle compared with the young subjects. Female subjects had significantly lower AUC (P=0.02) in the left orbicularis oculi muscle compared with males. The old subjects had significantly later offset (P<0.003) and longer duration (P<0.001) in the left orbicularis oculi compared with the young subjects. The results of the present study demonstrated a significant effect of both age and gender on stretch and BR and suggested that these variables should be taken into consideration in the interpretation of brainstem reflexes in basic and clinical studies.

Tension-type headache: Classification and diagnosis

Tension-type headache (TTH) is the most prevalent form of primary headache in the general population. In this article, the diagnostic challenges of TTH are discussed. The classification of these headaches according to the second edition of the International Classification of Headache Disorders (ICHD-2) and the main differences between the ICHD-2 and the first edition of the classification (ICHD-1, 1988) are discussed. The typical features of TTH also are highlighted. Finally, the differential diagnosis of episodic and chronic TTH, emphasizing the situations more likely to raise doubts, is discussed. The wide clinical spectrum of TTH frequently challenges the physician's diagnostic acumen. A structured approach to the patient and a better comprehension of this variability of presentation should translate into better quality of care and a more specific diagnosis for TTH sufferers.

EMG contamination of EEG: spectral and topographical characteristics

OBJECTIVE

Electromyogram (EMG) contamination is often a problem in electroencephalogram (EEG) recording, particularly, for those applications such as EEG-based brain-computer interfaces that rely on automated measurements of EEG features. As an essential prelude to developing methods for recognizing and eliminating EMG contamination of EEG, this study defines the spectral and topographical characteristics of frontalis and temporalis muscle EMG over the entire scalp. It describes both average data and the range of individual differences.

METHODS

In 25 healthy adults, signals from 64 scalp and 4 facial locations were recorded during relaxation and during defined (15, 30, or 70% of maximum) contractions of frontalis or temporalis muscles.

RESULTS

In the average data, EMG had a broad frequency distribution from 0 to >200 Hz. Amplitude was greatest at 20-30 Hz frontally and 40-80 Hz temporally. Temporalis spectra also showed a smaller peak around 20 Hz. These spectral components attenuated and broadened centrally. Even with weak (15%) contraction, EMG was detectable (P<0.001) near the vertex at frequencies >12 Hz in the average data and >8 Hz in some individuals.

CONCLUSIONS

Frontalis or temporalis muscle EMG recorded from the scalp has spectral and topographical features that vary substantially across individuals. EMG spectra often have peaks in the beta frequency range that resemble EEG beta peaks.

SIGNIFICANCE

While EMG contamination is greatest at the periphery of the scalp near the active muscles, even weak contractions can produce EMG that obscures or mimics EEG alpha, mu, or beta rhythms over the entire scalp. Recognition and elimination of this contamination is likely to require recording from an appropriate set of peripheral scalp locations.

EMG-interference pattern analysis

The EMG interference pattern, built up of single motor unit action potentials, may be analyzed subjectively, or objectively by computer aided, quantitative methods, like counting of zero-crossings, counting of spikes, amplitude measurements, integration of the area under the curve, decomposition techniques, power spectrum analysis and turn/amplitude analysis. Since the shape of the interference pattern of healthy muscles is dependent on age, sex, force, muscle, temperature, fatigue, fitness level, recording site and surrounding tissue, electrode type, sensitivity, filters, sampling frequency and threshold level, all methods of analyzing the IP have to be standardized. Quantitative methods of analyzing the EMG interference pattern may be used for monitoring botulinum toxin therapy of dystonia and spasticity, quantifying spontaneous activity, assessment of chronic muscle pain, neuro-urological and proctological function, and diagnosing neuromuscular disorders. For diagnostic purposes, the methods favored are those that use needle electrodes and do not require measurement or monitoring of muscle force. The most well-evaluated methods are those using turn/amplitude analysis, like the cloud methods and the peak-ratio analysis. Peak-ratio analysis has the advantage that reference limits are easy to obtain and that its utility is well established and confirmed by several investigations. Overall, automatic methods of EMG interference pattern analysis are powerful tools for diagnostic and non-diagnostic purposes.

The utility of interference pattern analysis

The interference pattern of the electrical activity of muscle can be quantified by amplitude measurements, different spike counting methods, and power spectrum analyses. Interference pattern analysis (IPA) methods are used to describe the degree of activation of different muscles, muscle fatigue, occupational work, muscles in chronic pain syndromes, disused muscle, and dystonic muscle treated with botulinum toxin. In patients with neuromuscular disorders, the turns/amplitude analysis is useful for diagnosis. High diagnostic yields can be obtained without force measurements, for example, by using the amplitude as an indicator of force (the peak ratio method) or plotting the amplitude against the turns (cloud analysis). The diagnostic possibilities of the power spectrum analysis and the motor unit firing rate obtained by decomposition techniques are still unclear.

Pathophysiological mechanisms of tension-type headache: a review of epidemiological and experimental studies

In this present thesis I have discussed the epidemiology and possible pathophysiological mechanisms of tension-type headache. A population-based study of 1000 subjects randomly selected from a general population, two clinical studies, and a method study of EMG recordings, were conducted. Tension-type headache was the most prevalent form of headache, with a life-time prevalence of 78% in a general adult population. Thirty percent were affected more than 14 days per year and 3% were chronically affected, i.e. had headache at least every other day. Females were more frequently affected than males, and young subjects more frequently affected than older subjects. Females were more sensitive to mechanical pressure pain and revealed more tenderness from pericranial muscles and tendon insertions than males, and young subjects were more pain-sensitive than older subjects. Significantly higher tenderness in pericranial muscles was found in subjects with tension-type headache compared to migraineurs and to subjects without any experience of headache. Tenderness increased significantly with increasing frequency of tension-type headache in both males and females, whereas no such relation was found for mechanical pain thresholds. The applied EMG methodology was fairly reliable and nonpainful, but due to intersubject variability paired studies should be preferred. Subjects with chronic tension-type headache had slightly increased EMG levels during resting conditions and decreased levels during maximal voluntary contraction compared with headache-free subjects, indicating insufficient relaxation at rest and impaired recruitment at maximal activity. In a subsequent clinical, controlled study, the effect of 30 min of sustained tooth clenching was studied. Within 24 h, 69% of patients and 17% of controls developed a tension-type headache. Shortly after clenching, tenderness was increased in the group who subsequently developed headache, whereas tenderness was stable in the group of patients who remained headache-free, indicating that tenderness might be a causative factor of the headache. Likewise, psychophysical and EMG parameters were studied in 28 patients with tension-type headache, both during and outside of a spontaneous episode of tension-type headache. It was concluded that a peripheral mechanism of tension-type headache is most likely in the episodic subform, whereas a secondary, segmental central sensitization and/or an impaired supraspinal modulation of incoming stimuli seems to be involved in subjects with chronic tension-type headache. Prolonged nociceptive stimuli from myofascial tissue may be of importance for the conversion of episodic into chronic tension-type headache. The author emphasizes that tension-type headache is a multifactorial disorder with several concurrent pathophysiological mechanisms, and that extracranial myofascial nociception may constitute only one of them. The present thesis supplements the understanding of the balance between peripheral and central components in tension-type headache, and thereby, hopefully, leads us to a better prevention and treatment of the most prevalent type of headache.

Muscular disorders in tension-type headache

In order to evaluate the diagnostic criteria for muscular disorders in tension-type headache, pericranial muscle tenderness and pressure pain thresholds were studied in a random sample population of 735 adults aged 25-64. In addition, quantitative EMGs were recorded in 547 of these subjects. The correlation between the three diagnostic tests was assessed and the discriminality and cut-off points were analysed using Receiver Operating Characteristics analysis. Local tenderness from the temporal muscles was closely related to the total tenderness scores from 14 pairs of muscles. In chronic tension-type headache, tenderness was positively related to EMG and inversely related to pain thresholds. In the episodic from the total tenderness score was inversely related to pain thresholds, whereas no significant relation to EMG was noted. The Receiver Operating Characteristics curves indicated that tenderness recorded by manual palpation was the most specific and sensitive test, whereas EMG and pain thresholds were of limited diagnostic value. Eighty-seven percent of subjects with the chronic, and 66% of subjects with the episodic form were found to have a "muscular disorder" defined as increased tenderness recorded by either manual palpation or pressure algometry and/or increased EMG levels. However, muscle tenderness increased significantly during pain, so the headache state should be considered in future studies. Suggestions for revision of the present diagnostic criteria for muscular disorders are given.

Needle EMG of the human diaphragm: power spectral analysis in normal subjects

Needle EMG of the diaphragm was performed in 43 diaphragms in 23 healthy volunteers. The mean +/- standard deviation for the median frequency (MF) of the power spectrum was 233.3 +/- 58.1 Hz. The MF increased with age and showed a negative correlation with the forced vital capacity (FVC), but there was no correlation with other anthropometric measures or the results of phrenic nerve conduction study. The higher MF in older subjects may be due to early recruitment of larger units. The negative correlation between MF and FVC is likely secondary to a lower level of contraction required for normal breathing in subjects with high FVC. The integrated EMG (iEMG) of each inspiration strongly correlated with the tidal volume and the duration of inspiration. Power spectral analysis of diaphragmatic EMG is feasible and reliable. It can be used to assess respiratory muscle fatigue and may help in the diagnosis of neuromuscular disorders affecting the diaphragm.

Mechanisms of spontaneous tension-type headaches: an analysis of tenderness, pain thresholds and EMG

Pericranial muscle tenderness, EMG levels and thermal and mechanical pain thresholds were studied in 28 patients with tension-type headache and in 30 healthy controls. Each patient was studied during as well as outside a spontaneous episode of tension-type headache. Outside of headache, muscle tenderness and EMG levels were significantly increased compared to values in controls subjects, while mechanical and thermal pain thresholds were largely normal. During headache, muscle tenderness evaluated by blinded manual palpation increased significantly, while pressure pain thresholds remained normal and pressure pain tolerances decreased. Thermal pain detection and tolerance threshold decreased significantly in the temporal region, but remained normal in the hand. EMG levels were unchanged during headache. It is concluded that one of the primary sources of pain in tension-type headache may be a local and reversible sensitization of nociceptors in the pericranial muscles. In addition, a segmental central sensitization may contribute to the pain in frequent sufferers of tension-type headache.

Epidemiology of headache

This thesis is based on nine previously published papers. It represents the first prevalence study of specific headache entities in a representative general population, where the diagnoses are based on a structural interview and examination by a physician using internationally accepted operational diagnostic criteria. The study population was a random sample of 1000 men and women aged 25-64. The participation rate was 76%. The prevalences of the different forms of headache are assessed and the study provides descriptive data concerning symptomatology, precipitating factors, impact of female hormones, use of medical services and work consequences of the headache disorders and describes various factors associated with the disorders. Only half of migraineurs and one-sixth of subjects with tension-type headache consulted their general practitioner because of headache and even less consulted a specialist. These consultation rates reflect the selection of cases that may bias studies in clinic populations. The study supports the notion that migraine and tension-type headache are separate clinical entities and that migraine without aura and migraine with aura are distinct subforms of migraine. Migraine and tension-type headache are sex- and age-dependent disorders with female preponderance and lower prevalence in older age groups. The female preponderance may be explained by clinical factors related to female hormones. There is no clear evidence of any association between sociodemographic variables and migraine or tension-type headache. Tension-type headache is related to a series of psychosocial variables while migraine is not. The results suggest that migraine is primarily a constitutional disorder and tension-type headache a more complex phenomenon influenced by several psychosocial factors. The limitations of cross-sectional data in pointing out risk factors with sufficient certainty are stressed. Longitudinal follow-up studies are the most important challenge in future epidemiological headache research.

Quantitative surface EMG of pericranial muscles in headache. A population study

Quantitative EMG from the right frontal and both temporal muscles was studied in 547 adults randomly selected from the general population. The study was part of a multifaceted, epidemiological study of different headache disorders. Surface EMG was recorded by an observer blinded to the persons' history of headache, previous illness and mental state. The present study provides data on amplitude and mean and median frequency levels in migraine and tension-type headache. Chronic headache sufferers had higher amplitude values at rest in their temporal muscles than migraineurs, subjects with episodic tension-type headache and subjects without any experience of headache, probably due to insufficient relaxation. Frequency values during maximal voluntary contraction were decreased in chronic headache subjects and decreased with increasing frequency of headache in the previous year, indicating that chronic fatigue and/or changed fiber type composition exist in frequent headache sufferers. During experimental cold and pain stimulation no significant differences between headache subjects and the rest of the population were detected. Only subjects without any experience of headache had increased amplitude values during pain stimulation. No significant relation of amplitude values to frequency of tension-type headache or migraine in the previous year was detected. In 66 subjects with actual headache amplitude values were increased in the frontal muscle during rest indicating increased tension. Moreover, amplitude values were decreased in both the temporal and the frontal muscles during maximal voluntary contraction indicating submaximal contraction during pain. The present study supports the importance of peripheral factors such as increased fatigability, morphological, and/or metabolic changes in the pathogenesis of tension-type headache. However, the diagnostic value of EMG in migraine and tension-type headache is limited.