Influences of head positions and bite opening on collapsibility of the passive pharynx.

A collapsible tube surrounded by soft material within a rigid box was proposed as a two-dimensional mechanical model for the pharyngeal airway. This model predicts that changes in the box size (pharyngeal bony enclosure size anatomically defined as cross-sectional area bounded by the inside edge of bony structures such as the mandible, maxilla, and spine, and being perpendicular to the airway) influence patency of the tube. We examined whether changes in the bony enclosure size either with head positioning or bite opening influence collapsibility of the pharyngeal airway. Static mechanical properties of the passive pharynx were evaluated in anesthetized, paralyzed patients with sleep-disordered breathing before and during neck extension with bite closure (n = 11), neck flexion with bite closure (n = 9), and neutral neck position with bite opening (n = 11). Neck extension significantly increased maximum oropharyngeal airway size and decreased closing pressures of the velopharynx and oropharynx. Notably, neck extension significantly decreased compliance of the oropharyngeal airway wall. Neck flexion and bite opening decreased maximum oropharyngeal airway size and increased closing pressure of the velopharynx and oropharynx. Our results indicate the importance of neck and mandibular position for determining patency and collapsibility of the passive pharynx.     

Mandibular movements of the albino rat during feeding

Jaw movements of albino rats during biting and mastication of relatively hard food were recorded by means of conventional and X-ray cinematography. Mandibular kinetics have been analysed in the context of passive mechanical limits imposed by jaw morphology, particularly of the joints, and by the food itself. Movements have been described in terms of degrees of gape, condylar translation and horizontal rotation of the rami about the symphysis. During biting the condyle remains in the anterior two-thirds of the fossa, moves forward as the jaw opens and the converse. The rami usually spread well apart; the lower incisors are usually approximated. Incised food particles are transported toward the molars by means of coordinated jaw and tongue movements. The prominent palatal rugae of the diastemal region abet this process. In the power stroke of mastication, the mandible shifts forward as the lower toothrows move a little inward; the condyles occupy the posterior two-thirds of the fossa. All movements seen were bilaterally symmetrical. Simultaneous chewing occurred on both sides. It is suggested that the lingual components in the primarily anterior power stroke enhance grinding efficiency. A movable symphysis appears to be of critical importance in facilitating this type of mastication.     

Cyclic analogs of enkephalin with disulfide bridges between the second and fifth positions

Biological activity of the enkephalin cyclic analogues with a disulphide bridge between second and fifth positions, and the dependence of the activity on the cycle size, disulfide bridge localization and configuration of the amino acid residues have been studied. The analogues were synthesized by chemical approach with the use of pentafluorophenyl esters. The cyclization was carried out at the C-terminal tetrapeptide stage by iodine in methanol after removing benzyl protecting groups from thiol groups of cysteine and homocysteine by sodium in liquid ammonia. The blocking activity in vitro (GPI and MVD tests) to the mu- and delta-receptors depends on cycle size, localization of disulphide bridge in the cycle, and amino acid configuration at second and fifth positions. Analogues with D-amino acids proved to be most active in vivo (analgesia, cataleptic activity, effect on frequency of heart contractions and body temperature). Conformational characteristics of enkephalin analogues were investigated by means of CD spectroscopy.     

A biomechanical model of the lumbosacral joint during lifting activities

A biomechanical model of the lumbosacral region was constructed for the purpose of systematically studying the combined stresses and strains on the local ligaments, muscles and disc tissue during sagittal plane two-handed lifting. The model was validated in two ways. The first validation was a comparison of experimental study results with model predictions. In general predictions compared very reasonably with observed values of several authors with the exception of strain predictions on the articular ligaments. Second, a sensitivity analysis was performed over a wide range of lifting tasks. The predicted stress/strain values followed anticipated patterns and were of reasonable magnitudes. On the basis of the results of the sensitivity analysis it was concluded that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains. Conversely, annulus rupture of a healthy disc due to overstrain appears very unlikely.     

Altered control of submaximal bite force during bruxism in humans

The control of bite force during varying submaximal loads was examined in patients suffering from bruxism compared to healthy humans not showing these symptoms. The subjects raised a bar (preload) with their incisor teeth and held it between their upper and lower incisors using the minimal bite force required to keep the bar in a horizontal position. Further loading was added during the preload phase. A sham load was also used. Depending on the session, the teeth were loaded by the experimenter or the subject and in one session the subject did not see the load (no visual feedback). The bite force was measured continuously using a calibrated force transducer. In all the subjects, the bite force increased with increasing load. Following the addition of the load, the level of the tonic bite force was reached rapidly with no marked overshoot. The patients with bruxism used significantly higher bite forces to hold the submaximal loads compared to the control subjects. In the control subjects, the holding forces for each submaximal load were identical in the men and the women and were independent of subject maximal bite force. Sham loading evoked no marked responses in biting force. Whether the subject or the experimenter added the load or whether the subject had visual feedback or not were not significant factors in determining the level of bite force. The results indicated that the patients with bruxism used excessively large biting forces for each given submaximal load. This study showed no evidence that the inappropriate control of bite force by patients with bruxism was due to an abnormality in the higher cortical circuits that regulates the function of trigeminal motoneurons in the brainstem. This was shown by a lack of abnormality in coordination of voluntary hand movement with biting force, a lack of abnormal anticipation response to a sham load and a lack of any effect of visual feedback. The results were in line with the hypothesis that afferent input from oral (periodontal or masticatory muscle) tissues does not provide an appropriate control of motor command in bruxism.     

The kinematics of the scapulae and spine during a lifting task

Simultaneous motion of the scapula and humerus is widely accepted as a feature of normal upper limb movement, however this has usually been investigated under conditions in which purposeful, functional tasks were not considered. The aim of this study was to investigate the synchrony and coordination of the constituent 3D movements of the shoulder girdle and trunk, during a functional activity. 45 healthy women, aged between 20 and 80 years, performed a simple lifting task, moving a loaded box from a shelf at waist level to one at shoulder level and then reversed the movement, during which the linear and angular motions of the scapulae, upper and lower thoracic spine and upper limbs were monitored and analysed using cross-correlation techniques. Results indicated a close and consistent set of coordinated movement patterns, which suggest biomechanical invariance in the responses of the structures adjacent to the upper limb during such a lifting task. These scapulohumeral relationships were, however, more constant and phase-locked when there was a specific purpose to the movement than during periods in which the arm was lowered without load. There were no age-related differences in any movement responses.     

Prediction of biomechanical parameters in the lumbar spine during static sagittal plane lifting.

A combined approach involving optimization and the finite element technique was used to predict biomechanical parameters in the lumbar spine during static lifting in the sagittal plane. Forces in muscle fascicles of the lumbar region were first predicted using an optimization-based force model including the entire lumbar spine. These muscle forces as well as the distributed upper body weight and the lifted load were then applied to a three-dimensional finite element model of the thoracolumbar spine and rib cage to predict deformation, the intradiskal pressure, strains, stresses, and load transfer paths in the spine. The predicted intradiskal pressures in the L3-4 disk at the most deviated from the in vivo measurements by 8.2 percent for the four lifting cases analyzed. The lumbosacral joint flexed, while the other lumbar joints extended for all of the four lifting cases studied (rotation of a joint is the relative rotation between its two vertebral bodies). High stresses were predicted in the posterolateral regions of the endplates and at the junctions of the pedicles and vertebral bodies. High interlaminar shear stresses were found in the posterolateral regions of the lumbar disks. While the facet joints of the upper two lumbar segments did not transmit any load, the facet joints of the lower two lumbar segments experienced significant loads. The ligaments of all lumbar motion segments except the lumbosacral junction provided only marginal moments. The limitations of the current model and possible improvements are discussed.     

Effects of Decreased Occlusal Loading during Growth on the Mandibular Bone Characteristics

Background

Bone mass and mineralization are largely influenced by loading. The purpose of this study was to evaluate the reaction of the entire mandibular bone in response to decreased load during growth. It is hypothesized that decreased muscular loading will lead to bone changes as seen during disuse, i.e. loss of bone mass.

Methods and Findings

Ten 21-day-old Wistar strain male rats were divided into two groups (each n=5) and fed on either a hard- or soft-diet for 11 weeks. Micro-computed tomography was used for the investigation of bone mineralization, bone volume, bone volume fraction (BV/TV) and morphological analysis. Mandibular mineralization patterns were very consistent, showing a lower degree of mineralization in the ramus than in the corpus. In the soft-diet group, mineralization below the molars was significantly increased (p<0.05) compared to the hard diet group. Also, bone volume and BV/TV of the condyle and the masseter attachment were decreased in the soft-diet group (p<0.05). Morphological analysis showed inhibited growth of the ramus in the soft-diet group (p<0.05).

Conclusion

Decreased loading by a soft diet causes significant changes in the mandible. However, these changes are very region-specific, probably depending on the alterations in the local loading regime. The results suggest that muscle activity during growth is very important for bone quality and morphology.     

Fetal growth in the baboon during the second half of pregnancy

The normal growth profile of critical fetal organs through the last third of gestation has not been documented in detail in human fetuses or the fetus of any nonhuman primate species. Recent epidemiological studies in human pregnancy suggest that fetal growth plays a major role in the programming of life-long health by modifying cardiovascular, pancreatic, brain, and liver growth. The present study aimed to produce a detailed database of individual organ growth in the fetal baboon in late gestation. Fetal organ weights were obtained from 43 baboon fetuses between 121 and 177 days of gestation. Various organs (brain, heart, kidney, femur, intestines, and spinal cord) showed no sign of slowed growth in late gestation while growth of others (lung, liver, stomach, and bladder) accelerated in late gestation. The fetal adrenal and thymus showed a decrease in growth rate over the final 20 and 10 days of gestation respectively. These observations provide a database that will permit analysis of factors responsible for regulation of normal and altered fetal organ development in this important experimental species.     

Cardiac output during exercise in paraplegic subjects

The purpose of this study was to measure the cardiac output using the CO2 rebreathing method during submaximal and maximal arm cranking exercise in six male paraplegic subjects with a high level of spinal cord injury (HP). They were compared with eight able bodied subjects (AB) who were not trained in arm exercise. Maximal O2 consumption (VO2max) was lower in HP (1.11.min, SD 0.1; 17.5 ml.min-1.kg-1, SD 4) than in AB (2.5 l.min-1, SD 0.6; 36.7 ml.min-1.kg, SD 10.7). Maximal cardiac output was similar in the groups (HP, 14 l.min-1, SD 2.6; AB, 16.8 l.min-1, SD 4). The same result was obtained for maximal heart rate (fc,max) (HP, 175 beats.min-1, SD 18; AB, 187 beats.min-1, SD 16) and the maximal stroke volume (HP, 82 ml, SD 13; AB, 91 ml, SD 27). The slopes of the relationship fc/VO2 were higher in HP than AB (P less than 0.025) but when expressed as a %VO2max there were no differences. The results suggest a major alteration of oxygen transport capacity to active muscle mass in paraplegics due to changes in vasomotor regulation below the level of the lesion.     

Comparison of muscle activation using various hand positions during the push-up exercise

Popular fitness literature suggests that varied hand placements during push-ups may isolate different muscles. Scientific literature, however, offers scant evidence that varied hand placements elicit different muscle responses. This study examined whether different levels of electromyographic (EMG) activity in the pectoralis major and triceps brachii muscles are required to perform push-ups from each of 3 different hand positions: shoulder width base, wide base, and narrow base hand placements. Forty subjects, 11 men and 29 women, performed 1 repetition of each push-up. The EMG activity for subjects' dominant arm pectoralis major and triceps brachii was recorded using surface electrodes. The EMG activity was greater in both muscle groups during push-ups performed from the narrow base hand position compared with the wide base position (p < 0.05). This study suggests that, if a goal is to induce greater muscle activation during exercise, then push-ups should be performed with hands in a narrow base position compared with a wide base position.     

Mandibular movement and muscle activity during mastication in the guinea pig (Cavia porcellus)

Optoelectronic analysis of mandibular movement and electromyography (EMG) of masticatory muscles in Cavia porcellus indicate bilateral, unilateral, and gnawing cycles. During bilateral and unilateral cycles, the mandibular tip moves forward, lateral, and down during the lingual phase of the power stroke to bring the teeth into occlusion. EMG activity is generally asymmetric, with the exception of activity of the temporalis muscle during bilateral cycles. During gnawing cycles, the mandible moves in an anteroposterior direction that is opposite that during bilateral and unilateral chew cycles. Bilateral and unilateral cycles of pellets were significantly longer than carrot. With the exception of the width of bilateral cycles, the magnitude of cycle width, length, and height during the mastication of carrots was greater than that during the mastication of pellets. Significant differences exist between EMG durations during mastication of pellets and carrots. The lateral pterygoid displays continuous activity during gnawing cycles. Significant differences also exist in the durations of EMG activity between the working and balancing side during all three cycle types. High level activity of balancing side temporalis and anterior belly of digastric (ABD) during bilateral cycles occurs during rotation and depression of the mandible during the power stroke. The temporalis apparently provides a ?braking”? or compensatory role during closing and power strokes. Differences between Cavia masticatory patterns and those shown by Rattus and Mesocricetus are apparently due to differences in dental morphology, occlusal relationships, and, possibly, the poorly developed temporalis in Cavia. The large number and wide diversity of rodent groups afford students of mammalian mastication an opportunity to investigate and compare different masticatory specializations.     

Modeling the precision and robustness of Hunchback border during Drosophila embryonic development

During anterior-posterior axis specification in the Drosophila embryo, the Hunchback (Hb) protein forms a sharp boundary at the mid-point of the embryo with great positional precision. While Bicoid (Bcd) is a known upstream regulator for hb expression, there is evidence to suggest that Hb effectively filters out “noisy” data received from varied Bcd gradients. We use mathematical models to explore simple regulatory networks which filter out such noise to produce a precise Hb boundary. We find that in addition to Bcd and Hb, at least one freely evolving protein is necessary. An automated search yields a number of examples of three-protein networks exhibiting the desired precision. In all such networks, Hb diffuses much slower than the third protein. In addition, the action of Hb on the third protein is the opposite of the action of the third protein on hb (i.e. if Hb activates the third protein, then the third protein inhibits hb expression, and vice versa). Most of the discovered systems satisfy the known biological properties, that Bcd activates hb, and that Hb activates its own expression. We find that all network topologies satisfying these constraints arise among the networks exhibiting the desired precision. Investigating the dynamics of these networks, we find that under a general class of non-uniform initial conditions, Bcd can be eliminated from the system and the spatiotemporal evolution of these two proteins alone is sufficient to recapture the dynamics. We hypothesize that Bcd is needed only to spatially disturb the gradient of the third protein, and then becomes unnecessary in the further evolution of the Hb border. This provides a possible explanation as to why the Hb dynamics are robust under perturbations of the Bcd gradient. Under this hypothesis, other proteins would be able to assume the role of Bcd in our simulations (possibly in the case of evolutionary divergences or a redundancy in the process), with the only constraint that they act to positively regulate hb.     

Surface EMG recordings during maximum static shoulder forward flexion in different positions

This study investigated how position in the range of motion influences the power spectral density function during static shoulder forward flexion. 23 healthy females (20-30 years) volunteered as subjects. They performed maximum static shoulder forward flexions in three positions: 45, 65 and 90 degrees of shoulder flexion. An isokinetic dynamometer was used and the subjects were seated in a specially constructed chair to enable adequate fixation. The elbow was extended and the hand pronated. Electromyographic (EMG) signals (using surface electrodes) were obtained from the descending part of the right trapezius, the anterior portion of the right deltoid, the right infraspinatus and the common belly of the right biceps brachii. The four EMG-signals and the torque and shoulder angle were analyzed by computer. For each 256 ms, mean power frequency, root mean square value and mean torque were calculated. At each of the three positions four 256 ms periods were analyzed and the data are presented as their means. In the trapezius and the biceps brachii the mean power frequency did not change between the three positions. Deltoid and infraspinatus had significantly higher mean power frequencies at 90 degrees than at 45 degrees of flexion. Different factors behind the change in mean power frequency are discussed. The need to standardize the range of motion when studying dynamic fatiguing contractions is emphasised.     

Evidence for a role of antagonistic cocontraction in controlling trunk stiffness during lifting

Activity of the abdominal muscles during symmetric lifting has been a consistent finding in many studies. It has been hypothesized that this antagonistic coactivation increases trunk stiffness to provide stability to the spine. To test this, we investigated whether abdominal activity in lifting is increased in response to destabilizing conditions.

Ten healthy male subjects lifted 35 l containers containing 15 l of water (unstable condition), or ice (stable condition). 3D-kinematics, ground reaction forces, and EMG of selected trunk muscles were recorded. Euler angles of the thorax relative to the pelvis were determined. Inverse dynamics was used to calculate moments about L5S1. Averaged normalized abdominal EMG activity was calculated to express coactivation and an EMG-driven trunk muscle model was used to estimate the flexor moment produced by these muscles and to estimate the L5S1 compression force.

Abdominal coactivation was significantly higher when lifting the unstable load. This coincided with significant increases in estimated moments produced by the antagonist muscles and in estimated compression forces on the L5S1 disc, except at the instant of the peak moment about L5S1. The lifting style was not affected by load instability as evidenced by the absence of effects on moments about L5S1 and angles of the thorax relative to the pelvis. The data support the interpretation of abdominal cocontraction during lifting as subserving spinal stability. An alternative function of the increased trunk stiffness due to cocontraction might be to achieve more precise control over the trajectory of lifted weight in order to avoid sloshing of the water mass in the box and the consequent perturbations.     

Cardiovascular responses in paraplegic subjects during arm exercise

The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 60% of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was significantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Qc between P and C; however, stroke volume (SV) was significantly lower and fc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc,max. During submaximal exercise, however, this lower SV was compensated for by a higher fc and, thus at the same submaximal oxygen uptake, Qc was similar to that in the control group.