Muscle Electromyogram Activity Research Articles

Comparison of EMG activity in shank muscles between individuals with and without chronic ankle instability when running on a treadmill

Changes in movement capabilities after an injury to the ankle may impose adaptations in the peripheral and central nervous system. The purpose of our study was to compare the electromyogram (EMG) profile of ankle stabilizer muscles and stride-time variation during treadmill running in individuals with and without chronic ankle instability (CAI). Recreationally active individuals with (n=12) and without (n=15) CAI ran on a treadmill at two speeds. EMG activity of four shank muscles as well as tibial acceleration data were recorded during the running trials. EMG amplitude, timing of EMG peaks, and variation in stride-time were analyzed from 30 consecutive stride cycles. EMG data were time-normalized to stride duration and amplitude was normalized relative to the appropriate maximal voluntary contraction (MVC) task. Individuals with CAI had similar EMG amplitudes and peak timing, but an altered order of peak EMG activity in ankle stabilizer muscles, a significantly greater EMG amplitude for PL with an increase in speed, and a greater stride-time variability during treadmill running compared with individuals who had no history of ankle sprains. The results of our study indicate that individuals with CAI exhibit altered activation strategies for ankle stabilizer muscles when running on a treadmill.

Visual recognition of words learned with gestures induces motor resonance in the forearm muscles

According to theories of Embodied Cognition, memory for words is related to sensorimotor experiences collected during learning. At a neural level, words encoded with self-performed gestures are represented in distributed sensorimotor networks that resonate during word recognition. Here, we ask whether muscles involved in gesture execution also resonate during word recognition. Native German speakers encoded words by reading them (baseline condition) or by reading them in tandem with picture observation, gesture observation, or gesture observation and execution. Surface electromyogram (EMG) activity from both arms was recorded during the word recognition task and responses were detected using eye-tracking. The recognition of words encoded with self-performed gestures coincided with an increase in arm muscle EMG activity compared to the recognition of words learned under other conditions. This finding suggests that sensorimotor networks resonate into the periphery and provides new evidence for a strongly embodied view of recognition memory.

The effect of neuromuscular electrical stimulation on muscle EMG activity and the initial phase rate of force development during tetanic contractions in the knee extensor muscles of healthy adult males.

Neuromuscular electrical stimulation (NMES) has been noted as an effective pre- contraction for an increase of neural and muscle factors during twitch contractions. However, it is unknown if this intervention is effective for the rate of force development (RFD), which is the ability to increase joint torque strength as quickly as possible, during tetanic contractions. NMES can be safely used by anyone, but, the strength setting of NMES requires attention so as not to cause pain. Therefore, the purpose of this study investigated whether NMES at less painful levels was effective for RFD during tetanic contractions. We also investigated effect activation by analyzing electromyogram (EMG) and RFD for each phase. Eighteen healthy males were studied. Before and after NMES intervention at 10% or 20% maximal voluntary isometric contraction (MVIC) level (10%NMES, 20%NMES respectively), EMG activity and the initial phase (30-, 50-, 100-, and 200-msec) RFD were measured. Visual analog scale (VAS) was also measured as an indicator of pain during each NMES. 20%NMES increased EMG activity and 30-, 50-, and 100-msec of RFD during MVIC, but could not improve 200 msec of RFD. However, 10%NMES could be failed to increase all phases RFD, but VAS was lower than that of 20% NMES. These results suggest that muscle pre-contraction using 20%NMES could induce moderate pain, but could be an effective intervention to improve RFD via neural factor activity.

Effects of textured foods on masticatory muscle activity in older adults with oral hypofunction.

Preserving sufficient oral function and maintaining proper nutrition are essential to prevent frailty. Thus, we have developed "munchy" foods that contain harder textures and are rich in protein. This study aimed to test the effects of masticating textured foods on masticatory muscle activity in young and older adults. Twenty young and 32 community-dwelling older individuals participated in this study. After measuring oral function, we subdivided the older participants into normal and oral hypofunction (OHF) groups. Two test foods (meatloaf and chicken ball) were prepared to have a harder texture using specific ingredients (munchy) or not (control). The participants ate 10g of the test foods in random order while being measured for masseter muscle activity with a surface electromyogram (EMG). We calculated the number of chewing cycles and integrated muscle activity of the masseter muscle from the EMG data and tested for differences by food texture or age group. The number of chewing cycles, mean EMG amplitude and integrated EMG activity was significantly higher for the munchy foods than for the controls for all groups. The integrated masseter muscle EMG activity was significantly increased in the normal older group than in the young group for both food types, but not significantly different between in OHF and young groups. Our findings suggest that eating textured foods will lead to increased masticatory load and therefore increased muscle activity, especially in older adults. Application of textured food may change dietary habits in older adults.

Acute Uterine Irritation Provokes Colonic Motility via Transient Receptor Potential A1-dependent Spinal NR2B Phosphorylation in Rats

Patients with inflammatory gynecological/obstetrical problems often complain of irritable bowel syndrome. The authors examined whether acute uterus irritation reflexively provokes colonic motility in rat preparations. A modified colon manometry and striated abdominal muscle electromyogram activity in response to mustard oil (MO) instillation into the uterine horn were continuously recorded in anesthetized rats. The lumbosacral (L6-S1) dorsal horn was dissected to assess the level and the cellular location of phosphorylated NR2B subunit using Western blotting and immunofluorescence analysis, respectively. Finally, the uterine transient receptor potential A1 or spinal NR2B subunit was pharmacologically blocked to elucidate its roles. MO (0.1%, 0.2 ml) injected into the lower uterine horn dramatically provoked colonic hypermotility characterized by rhythmic colonic contractions (about 3-4 contractions per 10 min, n = 7) accompanied by synchronized electromyogram firing in the abdominal muscle (about 4-5 folds of control, n = 7). In addition to provoking colonic hypermotility, MO administration also up-regulated phosphorylated (about 2-3 folds of control, n = 7), but not total, NR2B expression in the dorsal horn neurons. Both intrathecal Ro 25-6981 (a selective NR2B subunit antagonist; 10 μM, 10 μl) and intrauterine HC-030031 (a selective transient receptor potential A1 receptor antagonist; 30 mg/kg, 0.2 ml) injected before the MO instillation attenuated the MO-induced colonic hypermotility and spinal NR2B phosphorylation. The comorbidity of gynecological/obstetrical and gastrointestinal problems is not coincidental but rather causal in nature, and clinicians should investigate for gynecological/urological diseases in the setting of bowel problems with no known pathological etiology.

Obstacle avoidance locomotor tasks: adaptation, memory and skill transfer

The aim of this study was to explore the neural basis of adaptation, memory and skill transfer during human stepping over obstacles. Whilst walking on a treadmill, subjects had to perform uni- and bilateral obstacle steps. Acoustic feedback information about foot clearance was provided. Non-noxious electrical stimuli were applied to the right tibial nerve during the mid-stance phase of the right leg, i.e. 'prior' to the right or 'during' the left leg swing over the obstacle. The electromyogram (EMG) responses evoked by these stimuli in arm and leg muscles are known to reflect the neural coordination during normal and obstacle steps. The leading and trailing legs rapidly adapted foot clearance during obstacle steps with small further changes when the same obstacle condition was repeated. This adaptation was associated with a corresponding decrease in arm and leg muscle reflex EMG responses. Arm (but not leg) muscle EMG responses were greater when the stimulus was applied 'during' obstacle crossing by the left leg leading compared with stimulation 'prior' to right leg swing over the obstacle. A corresponding difference existed in arm muscle background EMG. The results indicate that, firstly, the somatosensory information gained by the performance and adaptation of uni- and bilateral obstacle stepping becomes transferred to the trailing leg in a context-specific manner. Secondly, EMG activity in arm and leg muscles parallels biomechanical adaptation of foot clearance. Thirdly, a consistently high EMG activity in the arm muscles during swing over the obstacle is required for equilibrium control. Thus, such a precision locomotor task is achieved by a context-specific, coordinated activation of arm and leg muscles for performance and equilibrium control that includes adaptation, memory and skill transfer.

Acute effect of muscle stretching on the steadiness of sustained submaximal contractions of the plantar flexor muscles

This paper examines the acute effect of a bout of static stretches on torque fluctuation during an isometric torque-matching task that required subjects to sustain isometric contractions as steady as possible with the plantar flexor muscles at four intensities (5, 10, 15, and 20% of maximum) for 20 s. The stretching bout comprised five 60-s passive stretches, separated by 10-s rest. During the torque-matching tasks and muscle stretching, the torque (active and passive) and surface electromyogram (EMG) of the medial gastrocnemius (MG), soleus (Sol), and tibialis anterior (TA) were continuously recorded. Concurrently, changes in muscle architecture (fascicle length and pennation angle) of the MG were monitored by ultrasonography. The results showed that during stretching, passive torque decreased and fascicle length increased gradually. Changes in these two parameters were significantly associated (r(2) = 0.46; P < 0.001). When data from the torque-matching tasks were collapsed across the four torque levels, stretches induced greater torque fluctuation (P < 0.001) and enhanced EMG activity (P < 0.05) in MG and TA muscles with no change in coactivation. Furthermore, stretching maneuvers produced a greater decrease (∼15%; P < 0.001) in fascicle length during the torque-matching tasks and change in torque fluctuation (CV) was positively associated with changes in fascicle length (r(2) = 0.56; P < 0.001), MG and TA EMG activities, and coactivation (r(2) = 0.35, 0.34, and 0.35, respectively; P < 0.001). In conclusion, these observations indicate that repeated stretches can decrease torque steadiness by increasing muscle compliance and EMG activity of muscles around the joint. The relative influence of such adaptations, however, may depend on the torque level during the torque-matching task.

Consequences of prolonged total thermoneutral immersion on muscle performance and EMG activity

We hypothesized that the changes in muscle temperature and interstitial pressure during thermoneutral immersion may affect the reflex adaptation of the motor drive during static contraction, assessed by the decrease in median frequency (MF) of electromyogram (EMG) power spectrum. Ten subjects were totally immersed for 6 h at 35 degrees C and repeated maximal voluntary contraction (MVC) and submaximal (60% MVC) leg extensions sustained until exhaustion. In vastus lateralis (VL) and soleus (SOL) muscles, the compound muscle potential evoked by muscle stimulation with single shocks (M-wave) was recorded at rest, and MF of surface EMG was calculated during 60% MVCs. We measured lactic acid and potassium venous blood concentrations and calculated plasma volume changes. Data were compared to those obtained in the same individuals exercising at 35 degrees C under dry conditions where the MF decrease during 60% MVCs was modest (-4 to-5%). During immersion, the rectal temperature remained stable, but the thigh and calf surface temperatures significantly increased. Lactic acid and potassium concentrations did not vary, but plasma volume decreased from the 180th min of immersion. The M-wave did not vary in VL but was prolonged in SOL from the 30th min of immersion. From the 220th min of immersion, the maximal MF decrease was majored in both muscles (-18 to -22%). Thus, compared to the dry condition, total body thermoneutral immersion enhances fatigue-induced EMG changes in leg muscles, perhaps through the activation of warm-sensitive muscle endings and/or the changes in interstitial pressure because of vasodilatation.

Muscle oxygenation and EMG activity during isometric exercise in children

The aim of this study was to examine the time-course of and the relationships between muscle oxygenation, blood volume and myoelectrical manifestations during isometric exercise in children. Twelve healthy children aged 12.5 ± 1.2 years (mean ± s) performed an isometric knee extension at 50% of their maximal voluntary contraction (MVC) until exhaustion to assess endurance time (limit time, T lim). Changes in muscle oxygenation and blood volume were assessed by near infrared spectroscopy (NIRS). The root mean square (RMS) amplitude and the mean power frequency (MPF) from electromyogram (EMG) signals were obtained, as NIRS parameters, from the vastus lateralis. Mean T lim was 117 ± 34 s. The muscle oxygenation and blood volume curves decreased immediately at the beginning of exercise. Maximal deoxygenation occurred at 50% T lim, and fell by 76.9% from the resting value. Similarly, minimal blood volume was observed at 50% T lim; it reached a plateau that lasted until the end of exercise. The kinetics of the MPF and RMS curves were inversely related to time. At the last set of exercises (after 75% T lim), a steeper RMS curve and an abrupt decrease in the MPF curve were observed. Significant correlations (r) between muscle oxygenation, blood volume, root mean square amplitude and mean power frequency were observed, which ranged from 0.72 to 0.99. These findings suggest that the fatigue resulting from sustained isometric exercise is related to a decrease in oxygenation and blood volume.

Spinal reflexes and coactivation of ankle muscles during a submaximal fatiguing contraction

This study examined the involvement of spinal mechanisms in the control of coactivation during a sustained contraction of the ankle dorsiflexors at 50% of maximal voluntary contraction. Changes in the surface electromyogram (EMG) of the tibialis anterior and of two antagonist muscles, the soleus and lateral gastrocnemius, were investigated during and after the fatigue task. Concurrently, the compound action potential (M-wave) and the Hoffmann reflex of the soleus and lateral gastrocnemius were recorded. The results showed that the torque of the ankle dorsiflexors and the average EMG of the tibialis anterior during maximal voluntary contraction declined by 40.9 +/- 17.7% (mean +/- SD; P < 0.01) and 37.0 +/- 19.9% (P < 0.01), respectively, at task failure. During the submaximal fatiguing contraction, the average EMG of both the agonist and antagonist muscles increased, leading to a nearly constant ratio at the end of the contraction when normalized to postfatigue values. In contrast to the monotonic increase in average EMG of the antagonist muscles, the excitability of their spinal reflex pathways exhibited a biphasic modulation. The amplitude of the Hoffman reflexes in the soleus and lateral gastrocnemius increased to 147.5 +/- 52.9% (P < 0.05) and 166.7 +/- 74.9% (P < 0.01), respectively, during the first 20% of the contraction and then subsequently declined to 66.3 +/- 44.8 and 74.4 +/- 44.2% of their initial values. In conclusion, the results show that antagonist coactivation did not contribute to task failure. The different changes in voluntary EMG activity and spinal reflex excitability in the antagonist muscles during the fatiguing contraction support the concept that the level of coactivation is controlled by supraspinal rather than spinal mechanisms. The findings indicate, however, that antagonist coactivation cannot simply be mediated by a central descending "common drive" to the motor neuron pools of the agonist-antagonist muscle pairs. Rather, they suggest a more subtle regulation of the drive, possibly through presynaptic mechanisms, to the motoneurons that innervate the antagonist muscles.

Control of human mandibular posture during locomotion.

Mandibular movements and masseter muscle activity were measured in humans during hopping, walking and running to determine whether reflexes contribute to the maintenance of jaw position during locomotion. In initial experiments, subjects hopped so that they landed either on their toes or on their heel. Landing on the toes provoked only small mandibular movements and no reflex responses in the masseter electromyogram (EMG). Landing on the heels with the jaw muscles relaxed caused the mandible to move vertically downwards relative to the maxilla, and evoked a brisk reflex response in the masseter at monosynaptic latency. Neither this relative movement of the mandible nor the reflex was seen when the teeth were clenched: hence the reflex is not the result of vestibular activation during head movement. The same variables were measured in a second series of experiments while subjects stood, walked and ran at various speeds and at various inclinations on a treadmill. During walking, the vertical movements of the head and therefore the mandible were slow and small, and there was no tonic masseter EMG or gait-related activity in the jaw-closing muscles. When subjects ran, the vertical head and jaw movement depended on the running speed and the inclination of the treadmill. Landing on the heels induced larger movements than landing on the toes. About 10 ms after each foot-strike, the mandible moved downwards relative to the maxilla, thereby stretching the jaw-closing muscles and activating them at segmental reflex latency. This caused the mandible to move back upwards. The strength of the reflex response was related to the speed and amplitude of the vertical jaw movement following landing. It is concluded that, during walking, the small, slow movements of the mandible relative to the maxilla are subthreshold for stretch reflexes in the jaw muscles: i.e. the mandible is supported by visco-elasticity of the soft tissues in the masticatory system. However, the brisker downward movements of the mandible after heel-landing during hopping and running evoke segmental reflex responses which contribute to the active maintenance of the posture of the mandible. This is a unique demonstration of how a stretch reflex operates to maintain posture under entirely natural conditions.

Low Frequency Cortico-Muscular Coherence During Voluntary Rapid Movements of the Wrist Joint

Rapid voluntary point-to-point wrist tracking movements are generated by the co-operative action of a large number of wrist muscles activated in a stereotypic pattern. This pattern is composed of a two burst sequence occurring in synergist and antagonist muscles. The time course and duration of these bursts are relatively fixed but the burst magnitude in any one muscle varies in relation to the direction of movement and the preferred directional tuning characteristic of the muscle. This creates a highly adaptive method for generating fast movements to different positions in space. In this study we have examined the extent to which this adaptive burst behaviour can be associated with activity changes occurring in the contralateral motor cortex. Time dependent coherence estimates were obtained from simultaneous recordings of the electroencephalogram (EEG) made from the contralateral sensorimotor cortex and the electromyogram (EMG) from various wrist flexor and extensor muscles during fast point-to-point wrist tracking movements. Using the onset of movement as a trigger, event related coherence estimates reveal the presence of short lasting periods of low frequency (<12 Hz) coherence during the execution of fast wrist movements. The onset and duration of the periods of low frequency coherence vary with direction of movement and the temporal burst profile of a particular muscle's EMG activity. It is therefore likely that a significant low frequency activation of the motor cortex plays a part in the generation of the EMG burst patterns that underpin rapid point-to-point movements of the human wrist.

Ictal pattern of EEG and muscular activation in symptomatic infantile spasms: a videopolygraphic and computer analysis.

To investigate ictal muscular phenomena characterizing symptomatic infantile spasms (ISs) and their relation to ictal EEG. Four children with severe encephalopathy, neurologic impairment, and refractory ISs related to different dysplastic lesions, underwent videopolygraphic recordings collecting surface electromyogram (EMG) activity from several cranial and limb muscles to evaluate the pattern of muscular recruitment, duration, and side-to-side asymmetry of ISs. Acquired data were stored for off-line analysis by a computerized polygraphic system. Spasms were characterized by a complex pattern of muscular activation. A constant or rostrocaudal propagation pattern was lacking in all patients. Intervals between the onset of EMG activity in different muscles in each spasm were very long: </=100-200 ms. Two patients, with hemispheric cortical dysplasia and agenesis of the corpus callosum, had asymmetric and asynchronous spasms in which the EMG onset of the muscles contralateral to the affected hemisphere constantly anticipated that of the ipsilateral ones. Backaveraging of EEG activity disclosed a high-amplitude EEG complex on the same side as the dysplastic lesion, preceding or succeeding the contralateral muscle activity onset. In the other two patients with diffuse cortical dysplasia, no EEG transient was related to EMG activity onset. Despite clinical similarity between spasms in the same patient, our data demonstrate the complexity and heterogeneity of these motor phenomena. Our findings cannot be explained simply in terms of cortical or reticular generators like other motor phenomena such as cortical myoclonus or startle reflex.

Prostaglandin D synthase in the prenatal ovine brain and effects of its inhibition with selenium chloride on fetal sleep/wake activity in utero.

It has been proposed that prostaglandin (PG) D(2) induces physiological sleep in mammals by acting on sleep centers located in the anterior hypothalamus. In fetal sheep, definitive rapid-eye-movement and non-rapid-eye-movement sleep states appear at approximately 125 d gestation (term is approximately 147 d). In adult animals, PGD synthase (PGDS) (functionally and structurally homologous to beta-trace protein) is secreted into CSF with a circadian pattern, with the highest concentrations present during sleep. In this study we show that PGDS/beta-trace protein is present in fetal sheep CSF at 125 and 135 d gestation but not at 90 d gestation. SeCl(4), a specific inhibitor of PGDS, was given to unanesthetized fetal sheep (130-140 d gestation) by intracerebroventricular infusion at a dose of 25, 100, 500, or 1000 pmol/min for 4 hr. Artificial CSF was infused in control experiments. Arousal behavior, defined as the presence of nuchal muscle electromyogram activity, electro-ocular activity, and breathing movements during low-amplitude electrocortical activity, increased from 3.8 +/- 1 min/hr to 6.6 +/- 0.5 and 7.0 +/- 0.3 min/hr at doses of 100 and 500 pmol/min, respectively (p < 0.05). SeCl(4) at 25 and 1000 pmol/min had no significant effect on arousal activity. Infusion of PGD(2) at 500 pmol/min intracerebroventricularly for 4 hr decreased the incidence of arousal from 3.8 +/- 0.5 min/hr to 0.7 +/- 0.3 min/hr (p < 0.05). When 500 pmol/min PGD(2) was infused immediately after a 4 hr infusion of SeCl(4) (500 pmol/min), the SeCl(4)-induced increase in arousal behavior was abolished. Together, the presence of PGDS/beta-trace protein in fetal CSF in late gestation and the effects of SeCl(4) in increasing the incidence of arousal-like behavior suggest that PGD(2) has a role in the induction and maintenance of prenatal sleep.

Prostaglandin D Synthase in the Prenatal Ovine Brain and Effects of Its Inhibition with Selenium Chloride on Fetal Sleep/Wake ActivityIn Utero

It has been proposed that prostaglandin (PG) D₂ induces physiological sleep in mammals by acting on sleep centers located in the anterior hypothalamus. In fetal sheep, definitive rapid-eye-movement and non-rapid-eye-movement sleep states appear at ∼125 d gestation (term is ∼147 d). In adult animals, PGD synthase (PGDS) (functionally and structurally homologous to β-trace protein) is secreted into CSF with a circadian pattern, with the highest concentrations present during sleep. In this study we show that PGDS/β-trace protein is present in fetal sheep CSF at 125 and 135 d gestation but not at 90 d gestation. SeCl₄, a specific inhibitor of PGDS, was given to unanesthetized fetal sheep (130–140 d gestation) by intracerebroventricular infusion at a dose of 25, 100, 500, or 1000 pmol/min for 4 hr. Artificial CSF was infused in control experiments. Arousal behavior, defined as the presence of nuchal muscle electromyogram activity, electro-ocular activity, and breathing movements during low-amplitude electrocortical activity, increased from 3.8 ± 1 min/hr to 6.6 ± 0.5 and 7.0 ± 0.3 min/hr at doses of 100 and 500 pmol/min, respectively (<i>p</i> &lt; 0.05). SeCl₄ at 25 and 1000 pmol/min had no significant effect on arousal activity. Infusion of PGD₂ at 500 pmol/min intracerebroventricularly for 4 hr decreased the incidence of arousal from 3.8 ± 0.5 min/hr to 0.7 ± 0.3 min/hr (<i>p</i> &lt; 0.05). When 500 pmol/min PGD₂ was infused immediately after a 4 hr infusion of SeCl₄ (500 pmol/min), the SeCl₄-induced increase in arousal behavior was abolished. Together, the presence of PGDS/β-trace protein in fetal CSF in late gestation and the effects of SeCl₄ in increasing the incidence of arousal-like behavior suggest that PGD₂ has a role in the induction and maintenance of prenatal sleep.

Quadriceps concentric and eccentric exercise 2: Differences in muscle strength, fatigue and EMG activity in eccentrically-exercised sore and non-sore muscles

The purpose of this study was to determine whether the previously reported muscle weakness and increases in EMG and EMG/force ratio after eccentric exercise were related to ensuing soreness or simply to the exercise mode. Delayed-onset muscle soreness, maximal voluntary force and the surface electromyogram (EMG) of the quadriceps were studied in 10 healthy male subjects following 20 min of bench-stepping with a constant leading leg. Prior to stepping and at 0, 0.25, 0.50, 0.75, 1, 3, 24 and 48 h afterwards the subjects performed a 30 s isometric maximal voluntary contraction (MVC) of the extensors of each leg during which the isometric force and the root mean square voltage of the surface EMG (rms EMG) were recorded. Muscle soreness was recorded prior to and at 0, 0.75, 3, 24 and 48 h after the stepping task by means of a force probe. No soreness was experienced in the concentrically exercised muscles, but in the eccentrically exercised muscles 5 subjects were not sore and 5 experienced soreness after 24 h, increasing to 48 h. There were no significant differences between sore and non-sore muscles in muscle weakness, fatigue during 30 s, the EMG amplitudes or the EMG/force ratios during peak force and the 30 s MVC (p >0.05). Muscle weakness following eccentric exercise was related to the exercise mode and was independent of subsequent soreness. Both weakness and soreness may be related to muscle damage, but involve different mechanisms.

Developmental changes in respiratory, febrile, and cardiovascular responses to PGE(2) in newborn lambs.

PGE(2) has centrally mediated respiratory, febrile, and cardiovascular effects that markedly differ between fetal and adult life. We hypothesized that the transition from fetal to adult responses to PGE(2) occurs in the newborn period. Thus effects of an intracarotid infusion of PGE(2) (3 microg/min for 60 min) were determined in unanesthetized newborn lambs at 5, 10, and 15 days after birth. At 5 days, PGE(2) reduced central CO(2) sensitivity, reduced lung ventilation due to a decrease in breathing frequency, and induced hypercapnia. By 15 days, these effects of PGE(2) had waned significantly. In contrast, phasic (expiratory) thyroarytenoid muscle electromyogram activity, number of short apneas, and incidence of Biot periodic breathing were similarly increased at all three ages. PGE(2) induced a sustained fever at 10 and 15 days. Heart rate and mean arterial blood pressure were unchanged in contrast to marked increases observed by others in adults. Results showed that the transition from fetal to adult respiratory and febrile responses to PGE(2) occurs in early postnatal life, whereas adult cardiovascular responses develop later in life in sheep.

Cutaneous withdrawal reflexes of the upper extremity.

We characterized reflexes of the upper limb elicited by electrical stimulation of the fingers. Surface electromyogram (EMG) was recorded from several upper extremity muscles, and a finger was stimulated through paired ring electrodes. A train of 4-10 shocks at a frequency of 300 Hz and an intensity 4-6 times the perceptual threshold was the most effective stimulus for evoking EMG activity in relaxed arm muscles. Habituation was prominent. Latencies of EMG activity were <100 ms for most proximal and forearm muscles, and at least 40 ms prior to voluntary withdrawal movements. The timing of EMG activity in arm muscles was similar to that of the E2 component of the cutaneomuscular reflex evoked in these same muscles during contraction, and coincided with a silent period in active hand muscles. We conclude that cutaneous stimuli to the fingers activate a complex motor pattern that tends to withdraw the hand at the same time the grasp is released.

Effect of pulsatile oxytocin administration to the pregnant ewe in the last third of gestation on fetal ACTH and cortisol response to acute hypoxemia.

The aim of this study was to examine the effect of increased myometrial contractility throughout the last third of pregnancy on the ovine fetal response to short-term hypoxemia. Oxytocin (600 microU/kg/minute, n = 5) or saline (n = 7) was infused for 5 minutes every 20 minutes into the maternal jugular vein starting at 95-99 days of gestation and continuing throughout the last third of gestation. Fetuses were subjected to a hypoxemic challenge (1 hour) at 131 days of gestation while fetal plasma ACTH and cortisol levels and nuchal muscle electromyogram activity were monitored. The fetal plasma ACTH concentration before and during the hypoxemic challenge was similar in the control and oxytocin groups. The fetal plasma cortisol concentration in the oxytocin group was significantly lower before and during the hypoxemia than in the controls. During hypoxemia, fetal nuchal muscle activity was significantly reduced only in the control group. Increased myometrial contracture frequency throughout the last third of pregnancy alters both the neuroendocrine and behavioral responses of fetal sheep to short-term hypoxemia.

Palatal muscle electromyogram activity in obstructive sleep apnea.

Eight subjects (5 men, 3 women, ages 27 to 55) with obstructive sleep apnea syndrome (OSAS) were studied to quantify and compare electromyographic (EMG) activity of levator veli palatini (LVP) and palatoglossus (PG), two velopharyngeal muscles, and genioglossus (GG) during obstructive apnea cycles in non-rapid eye movement (NREM) sleep. EMG activity of three successive preapneic breaths, first and last apneic efforts, and three successive postapneic breaths was quantified for each muscle as peak phasic inspiratory EMG normalized as percent activity of the last preapneic breath. In all subjects, apnea onset coincided with simultaneous inspiratory EMG nadir of all three muscles (LVP = 63 +/- 40%, PG = 74 +/- 53%. GG = 83 +/- 48%. mean +/- SD activity of last preapneic breath). Apnea resolution did not occur until inspiratory EMG of all three muscles simultaneously reached maximal activity, at levels significantly greater than preapneic activity as well as activity of the last preapneic effort (LVP = 215 +/- 205%, PG = 227 +/- 240+, GG = 235 +/- 202%, mean +/- SD activity of last preapneic breath, p < 0.05, Fisher's partial least-squares difference [PLSD] test for each muscle). The presence or absence of electroencephalographic arousal at apnea resolution did not influence these patterns of EMG activity. Inspiratory recruitment of velopharyngeal as well as oropharyngeal muscles appears to be associated with upper airway patency during sleep in patients with OSAS.