Suppression of Electron Thermal Conduction by Whistler Turbulence in a Sustained Thermal Gradient.

The dynamics of weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field is explored with particle-in-cell simulations and modeling. Two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude, δB/B_{0}≃1, and resonantly scatter the electrons, significantly reducing the heat flux. Surprisingly, the resulting steady-state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high-ß astrophysical plasmas such as hot accretion flows and the intracluster medium of galaxy clusters.

Assessment of the calcification of the nuchal ligament and osteophytes of the cervical spine in obstructive sleep apnoea subjects and snorers.

The previous reports suggest that obstructive sleep apnoea (OSA) is related to metabolic syndrome, mineral metabolism disorders and cardiovascular disease. In addition, a possible relationship between obesity and the calcification of ligaments has been implied. However, the potential link between OSA and the calcification of ligaments has not been directly studied. In this present study, to investigate the potential link between OSA and the calcification of ligaments, we examined the prevalence of the calcification of ligaments in OSA patients and the relationship between these findings and OSA severity. Eighty consecutive patients (60 males, 20 females) diagnosed as OSA or a heavy snorer based on full-night polyso-mnography were retrospectively recruited from May 2006 to July 2008. Each patient underwent cephalometric imaging examination before the arrangement of an oral appliance. One calibrated observer (YS) reviewed the cephalometric images for the presence of calcification of the nuchal ligament and osteophytes of the cervical spine. The prevalence of calcification of the nuchal ligament in OSA patients and snorers was 46.3% (males: 52%, females: 30%) There was a significant positive correlation between the severity of OSA (AHI) and the calcification of the nuchal ligament before and after adjusting for BMI. The prevalence of the calcification of the nuchal ligament in OSA subjects and snorers was higher than in previous studies with non-OSA subjects. In addition, it is suggested that the severity of OSA correlates with the presence of calcification of the nuchal ligament.

Occlusal dysesthesia: a qualitative systematic review of the epidemiology, aetiology and management.

Occlusal dysesthesia refers to a persistent complaint of uncomfortable bite sensation with no obvious occlusal discrepancy. This systematic review aimed to draw a picture of such patients, to present an agreement of previously reported diagnostic criteria and to analyse the evidence level of the recommended management approaches. An electronic search for all relevant reports on occlusal dysesthesia was thoroughly performed based on previous nomenclatures (e.g. phantom bite, occlusal hyperawareness) in PubMed and The Cochrane Library in July, 2011. A total of 84 reports were matched, among which only 11 studies were included after a two-step (abstract and detailed full-text revision) screening process. Additionally, a thorough manual review of reference lists of the included reports enabled the inclusion of two additional studies. Data analysis revealed that 37 occlusal dysesthesia patients presented a mean age of 51.7 ± 10.6 years and were predominantly women (male/female: 1/5.1) with symptom duration of more than 6 years (average: 6.3 ± 7.5 years) and with concomitant psychological disturbances (e.g. mood disorders, somatoform disorders, personality disorders). Only four authors presented diagnostic criteria for occlusal dysesthesia, which served as the basis for an agreement in the diagnostic criteria. Treatment approaches included psychotherapy, cognitive/behaviour therapy, splint therapy and prescription of anti-depressants or anti-anxiety drugs. Classification of evidence level of management approaches, however, revealed that most of them were expert opinions with single- or multiple-case report(s). Future studies are necessary for a deeper understanding of the mechanisms behind the occlusal dysesthesia symptoms, and consequently, for improvements in evidence-based management approaches.

Changes in three dimensional simulation models of the airway which are due to increases in age or body mass index.

The aim of this study was to model the changes in the soft and hard tissues that occur around the upper airway with increasing age and weight, and to visually gauge them through the use of 3D simulation models. We created two standard 3-dimensional models, with one set to represent a healthy subject model and the other serving as an OSA model. The results of the regression models in our anatomical variables were attached to each 3D model. We compared our data with the data of previous studies to recognize the validity of our regression model. In both models the pharyngeal length increased as age increased. We observed an increase in the fat tissue, soft palate length, and a thickening of the soft palate as BMI increased. As age and BMI increased, the narrowing of the airway appeared more severe in the OSA model.

Mandibular advancement devices and sleep disordered breathing.

It has been nearly 90 years since a dentist first fabricated a dental appliance for a patient with snoring. Since then, mandibular advancement devices or MADs have become a common treatment for obstructive sleep apnea and are used to increase the caliber of the airway during sleep. Their primary use is for the patient who has snoring or mild to moderate, but not severe, OSA problems. Unfortunately, only a small amount of empirical data exists on the topics of long-term compliance, complications and contraindications for these devices. Nevertheless, it appears that only a small percentage of patients will quit using a MAD because of temporomandibular joint (TMJ) or masticatory muscle soreness. An even smaller percent of the long-term MAD users will get changes in their occlusion. Compliance reports suggest that only 50% of the patients will be using the device after 3 years. Overall, these data suggest that MADs should be carefully fabricated by dentists who work on a referral basis with sleep medicine physicians and patients using MADs must be monitored regularly for ongoing efficacy and for associated complications. The good news (with good data support for this conclusion) is that MAD's are a moderately effective treatment of snoring and mild to moderate OSA.

A crossover study comparing the efficacy of continuous positive airway pressure with anterior mandibular positioning devices on patients with obstructive sleep apnea.

OBJECTIVE: This study compared the efficacy of a removable anterior mandibular positioning (AMP) device to continuous positive airway pressure (CPAP) in patients with obstructive sleep apnea (OSA) using a fully balanced crossover design. DESIGN: Twenty-three male subjects with confirmed OSA were recruited from the Technion Sleep Laboratory in Haifa, Israel, from February 18, 1991 to December 17, 1992. Twenty-one of the 23 subjects enrolled completed all aspects of the study. RESULTS: The mean apnea-hypopnea index (AHI) before treatment was 33.86 +/- 14.30. The mean AHI decreased with CPAP to 59.50%, but decreased only 38.91% with the AMP device. The lowest mean recorded oxygen saturation level for the 21 subjects was 84.30 before treatment, 91.10 after CPAP treatment, and 90.20 after AMP treatment. Sleep data revealed a significant decrease in stage 1 and 2 (p=0.0088) and an increase in rapid eye movement percent (p=0.0066) for both treatments when compared with baseline. Three- to 10-month posttreatment phone interviews showed that 1 subject was not using either device, 1 subject was using CPAP, and 2 subjects were using the AMP device intermittently due to occasional temporomandibular joint pain symptoms. The remaining 17 subjects were all using the AMP device nightly. The symptoms of excessive daytime sleepiness also decreased significantly by both AMP and CPAP. CONCLUSIONS: The AMP device achieved substantial success in most cases, but was less effective than CPAP, especially for the more severe cases. In general, the AMP device was strongly preferred over the CPAP by the subjects of this study.

Effect of jaw position and posture on forced inspiratory airflow in normal subjects and patients with obstructive sleep apnea.

OBJECTIVE: This study evaluated whether substantial airflow changes occur by changing both body posture and jaw position in normal subjects and patients with obstructive sleep apnea (OSA). DESIGN: A case-control design was utilized to assess group differences (OSA vs control) and each subject served as his/her own control subject to assess condition differences (jaw position and body posture changes). Subjects included 16 male patients with OSA (aged 33 to 71 years) whose conditions were diagnosed at the UCLA Sleep Disorders Laboratory with a polysomnographic recording, and 9 male non-OSA subjects (aged 22 to 52 years). The experimental intervention in the study involved alterations in body posture and jaw positioning. Airflow changes were determined using a spirometer that assessed the velocity of airflow during a forced inspiration. Subjects in this study all had the middle portion (25 to 75%) of their maximum forced inspiratory flow (FIF25-75) curve measured in three positions; (1) normal jaw position-upright body posture (N-U); (2) normal jaw position-supine body posture (N-S); and (3) protrusive jaw position-supine body posture (P-S). SETTING: The study was conducted at the UCLA Dental Clinical Research Center. RESULTS: Both groups had a significant decrease in their FIF25-75 upon reclining, and there were no significant group differences regarding the magnitude of this change. Both groups also had a nearly full recovery of their FIF25-75 airflow when their jaws were positioned forward while reclining. CONCLUSIONS: These data document that when a patient is in a supine position, a 100% protrusive jaw position allows significantly more inspiratory airflow to occur.

Cold pressor stimulation effect on hemodynamic changes following sustained isometric contraction in human jaw-closure muscles.

It is postulated that an altered adrenergic response pattern may be associated with chronic muscle pain states. To evaluate this hypothesis, one must fully understand the effect of an adrenergic activation on masticatory muscle blood flow under various conditions. This study evaluated the effect of a 12 degrees C cold pressor stimulation (a mild adrenergic activator), applied to the hand-forearm area, on intramuscular hemodynamics in the human masseter and temporalis muscles following a sustained isometric contraction. We assessed hemodynamics by measuring intramuscular hemoglobin concentration repeatedly, using a non-invasive near-infrared spectroscopy device. Measurements were taken before, during, and after a 30-second sustained 50% maximum voluntary contraction task. Fourteen healthy subjects, seven males and seven females, with no history of muscle pain in the masticatory system participated in this study. This protocol was repeated three times, but in the second trial, the cold pressor stimulation was applied to the subject during and for 5 min after the sustained contraction task. Repeated-measure analysis of variance performed on these data revealed that the peak hemoglobin concentration levels in the post-contraction recovery period were significantly reduced (between 13 and 14%) with cold pressor stimulation, both in the masseter (p < 0.001) and in the temporalis (p < 0.001) muscles. The results suggest that cold pressor stimulation produced a reduced intramuscular vasodilative response in these muscles during the immediate post-contraction period. One explanation for these results is that altering the local chemical environment of the muscle affects the adrenergic response pattern typically induced by a cold pressor stimulation.

Co-activation of sternocleidomastoid muscles during maximum clenching.

In an attempt to determine the degree of co-activation present in selected cervical muscles during clenching, we instructed 12 male subjects to produce four brief maximum voluntary contraction (MVC) efforts (clenching) in a position of maximum intercuspation. Surface EMG activity was recorded bilaterally from the masseter and sternocleidomastoid (SCM) muscles. The contraction level for the SCM during clenching was reported as a percentage of the SCM's maximum activity achieved during maximum neck flexion against resistance. All EMG signals for the masseter and SCM were converted to a true RMS voltage signal and digitized at a 100-Hz sampling rate. Mean peak EMG voltage levels were determined for the activity recorded during each brief MVC task. All subjects demonstrated co-activation of the SCM during strong abrupt clenching efforts. The mean levels (+/- S.D.) of SCM activity were 11.8 +/- 9.6% (right) and 14.2 +/- 9.4% (left) of the MVC capacity. Fifty percent of masseter activity was required to achieve 5% activity of the SCM bilaterally, and there was a progressive development of the SCM co-activation which paralleled the masseter activation.

Sternocleidomastoid muscle inhibition induced by trigeminal stimulation.

Among numerous reports of anatomical and functional coupling between the trigeminal and cervical systems is the demonstration that the sternocleidomastoid (SCM) muscles may become activated along with the masseter muscles during forceful abrupt biting maneuvers. Whether the co-activated SCM is also inhibited by stimuli that produce masseter inhibition is not known. This study evaluated the SCM for the presence of inhibition during mechanically-elicited (chin or forehead tap) and electrically-elicited (anterior maxillary gingiva stimulation) inhibition of the masseter muscle in ten healthy men. Surface EMG data were recorded bilaterally from the masseter and SCM muscles. The data for each muscle were converted to ratios of the pre-stimulus maximum voluntary contraction activity for each subject and averaged across subjects. Means of these percentages were determined at several defined pre- and post-stimulus intervals. The results indicate that masseter inhibition was clearly elicited by the electrical and both forms of mechanical stimulation. SCM co-inhibition could be evoked by electrical and chin tap stimulation but not by forehead tap. The responses to these stimuli varied among subjects, from trial to trial, and within subjects depending on the experimental condition. The fact that it was possible for this co-inhibition to be evoked is presented as further indication of the functional coupling of the trigeminal and cervical systems.

Nocturnal masseter muscle activity and urinary catecholamine levels in bruxers.

Nocturnal electromyographic recordings of masseter muscle activity were performed on 20 bruxist and ten control subjects. Each subject collected two 24-hour urine samples. An analysis of urinary catecholamine content was performed. A positive relationship was found between increased epinephrine content and high levels of nocturnal masseter muscle activity.

Jaw pain and stiffness levels after repeated maximum voluntary clenching.

Ten normal male volunteers performed six maximum voluntary isometric jaw-closing muscle contractions within an 80-minute experimental period. Each individual contraction was sustained until maximum pain tolerance was reached. Before and one, two, three, and seven days after the experiment, the following measures were made: (1) superficial masseter and anterior temporalis muscle tenderness (pain threshold), (2) jaw movement (opening and lateral excursion), and (3) current pain level for the right and left sides of the jaw. In this study, measures of current jaw pain, muscle pain threshold, maximum active opening, and maximum lateral excursions showed no significant post-experimental changes. These results challenge the idea that sustained isometric clenching in healthy male subjects could be used as a model for chronic or even subacute muscle pain, as has been suggested by previous investigators.

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels.

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

The effect of altering jaw position on the transmission of vibration between the skull and teeth in humans.

The forces that develop in the human temporomandibular joint during function have never been directly measured, yet many patients exhibit excessive localized wear and tear of the joint, suggesting that at times these forces exceed tissue tolerance. The purpose here was to gain insight into vibration transmission between the cranium and mandible in healthy humans during variations of jaw position. In 13 normal healthy adult men (age 25-40 years) with normal dentitions, vibration (around 400 Hz, sine wave) was applied to the skull vertex and changes in the intensity of the vibration signal were measured using several small linear accelerometers cemented to the buccal surfaces of mandibular first molars and the labial surfaces of maxillary central incisors. The jaw was opened, protruded and moved laterally by the individual participant and vibration signal intensities were tested (lower first molar signal/upper incisor signal) for change at each mandibular position by ANOVA. The results showed the vibration signal changed significantly with opening and less so on protrusion and laterotrusion. The vibration signal during opening could be categorized into three types: (1) signal increased continuously with increased opening; (2) signal increased, then reached a plateau during last third of opening; (3) signal increased, then decreased when the individual moved from 40 mm to maximum opening. These findings show that as the jaw moves laterally, and especially as it opens, the magnitude of the vibration signal increases substantially compared with the near-closed position.

Electromyographic study of human jaw-closing muscle endurance, fatigue and recovery at various isometric force levels.

The effect of a sustained isometric clenching, at various force levels or maximum voluntary bite-force levels, was evaluated on normal jaw-function subjects. Surface electromyographic (EMG) recordings of the masseter and temporalis were taken and bite force was measured using an intra-oral force transducer placed unilaterally in the 2nd premolar-1st molar region. Subjects sustained isometric force at the 25, 50, 75 and 100 per cent force level. Maximal bite force and EMG contraction levels were measured before, during and after these sustained isometric tasks. Subjects showed no change in their brief maximal contraction or force levels during or after various fatigue-inducing isometric tasks. The findings suggested a lack of contractile failure in the jaw-closing muscles. Pain intolerance rather than neuromuscular fatigue is the limiting factor of a sustained submaximal or even maximal clenching effort.

Factors influencing the excitatory-masseteric reflex evoked by gingival electrical stimulation in man.

An excitatory-masseteric reflex response was evoked by electrical gingival stimulation in five subjects; the reflex had an onset latency of 7.6 ms with a SD of 0.7 ms. The response occurred just prior to the silent or inhibitory period. There was consistent post-inhibitory synchronization of the EMG activity record in all subjects. Several methods were used to demonstrate this short-latency reflex. The first was to average non-rectified EMG activity. The second was to increase the number of receptors which are simultaneously activated by using multiple electrodes so that a greater area of gingiva could be stimulated. A third was to increase the level of excitability of the motoneurons in the masseteric pool by increasing voluntary bite force. Fourthly, the excitatory reflex was evoked during increased-excitatory drive to the pool, with the additional feature that the reflex appeared at a time when no ongoing EMG activity was present in the masseter muscle. Little doubt should now remain concerning the existence of a short latency excitatory reflex from intra-oral receptors to masseteric motoneurons in man.

Retrusive endurance, fatigue and recovery of human jaw muscles at various isometric force levels.

The effect of a sustained isometric retrusive contraction on maximum voluntary retrusive force levels was measured in normal jaw function. Surface electromyographic recordings of the suprahyoids, masseter and posterior temporalis were taken and force was measured with a force transducer. Subjects sustained isometric force at the 25, 50, 75 and 100 per cent level, and measurements made before, during and after these sustained isometric tasks. There was no change in the brief maximum voluntary contraction levels of the retruder muscles during or after such tasks, which suggests a lack of contractile or electrical failure in these muscles. Pain intolerance, rather than demonstrable neuromuscular fatigue, was the limiting factor for sustained submaximal or even maximal contraction effort.

Endurance and recovery from a sustained isometric contraction in human jaw-elevating muscles.

Ten males sustained maximal voluntary contractions (MVC) of the jaw elevators. Unilateral bite force and electromyographic (EMG) activity were recorded from the right masseter and temporalis. The experiment comprised three endurance trials, and each trial consisted of two sustained 100% MVC clenching tasks. Between the two tasks, the subjects took a randomly assigned rest of either 30, 120 or 300 s. Immediately after each task, they performed an additional brief 100% MVC to check for contractile failure. EMGs were taken from the beginning and end of each sustained 100% MVC and used to determine and compare the EMG centre frequency. The difference in endurance times between the first and second clenchings was greatest for the 30-s rest and progressively decreased as the rest period increased. The beginning EMG centre frequency was significantly greater than the end for each clenching. These findings strongly support the proposal that even though the jaw elevators are resistant to a contractile element failure, a contraction-induced pain is produced, which limits a sustained jaw-closing effort. Recovery from this effort pain is related to the post-contraction blood flow.

Electromyographic signal changes during exercise in human chronic jaw-muscle pain.

Twelve individuals (2 males, 10 females) with chronic masticatory muscle pain and 11 individuals (2 males, 9 females) without, had their bite force and surface electromyography from the right and left superficial masseter and anterior temporalis muscles recorded before, during and after a 30-s sustained submaximal clenching task. This task was performed at 50% of the force level of each subject's maximum voluntary contraction (MVC) for 30 s. Brief (3 s) 50% MVC efforts were recorded at 15-s intervals, three times before and six times after the sustained clench. Each subject performed this pattern of activities three times with a 15-min rest between each trial. The centre frequency (CF) of the electromyographic power spectrum was calculated by fast Fourier transformations. The mean CF at the end of the 30-s clench and the rate of change at the CF during the clenching task were analysed between groups, sides and muscles. The data indicated that the masseter CF decreased at a significantly faster rate for the first clenching trial in the muscle-pain group. Conversely, the rate of change of the temporalis CF did not significantly differ for the two groups during the three clenching trials. By the third trial the CF of the exercised masseter in the non-pain group exhibited a similar rate of change to that in the pain group. This suggests that both repeated exercise and the presence of chronic inflammation increase the rate of change of the electromyographic signal of the contracting masseter. The mechanism underlying this increased change is unknown.

Effect of cold pressor stimulation (4 degrees C) on human masseter muscle haemodynamics during and after sustained isometric contraction.

The effect of cold pressor (CP) stimulation and sustained isometric contraction on the blood volume of the right masseter muscle was examined in seven healthy males, who performed 1 min of isometric jaw clenching at 50% of their maximum voluntary contraction without, with and again without a 4 degrees C CP stimulation. Total haemoglobin was measured in the masseter before, during and after the contraction task using near-infrared spectroscopy. CP stimulation during the isometric contraction diminished the magnitude of the contraction-induced decrease of blood volume when compared to the trials without CP stimulation. However, in the immediate post-contraction period (while the CP stimulation was still in place), no increase in blood volume above the usual post-contraction hyperaemia was evident. Once the CP stimulation had been removed, there was a clear decrease (faster return to baseline) in the vasodilation occurring in the post-contraction period. This diminished period of vasodilation occurred in spite of the fact that the vascular resistance (blood pressure) and heart rate were still substantially elevated by the CP effect during this same period. These data suggest that the strong CP stimulation produced a biphasic response. First, there was an early-onset strong vasodilation (during CP), which was followed by a period of diminished vasodilation, suggesting that an active, but delayed, vasoconstrictive drive may be induced by the CP stimulus.