Phasic Electromyographic Activity Research Articles

Familial α-synucleinopathy spectrum features in patients with psychiatric REM sleep behaviour disorder

BackgroundRapid eye movement (REM) sleep behaviour disorder (RBD) is one of the earliest and most specific prodromes of the α-synucleinopathies including Parkinson’s disease (PD). It remains uncertain whether RBD occurring...

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Rapid eye movement (REM) sleep without atonia (RWA) is observed in some patients without a clinical history of REM sleep behavior disorder (RBD). It remains unknown whether these patients meet the refined quantitative electromyographic (EMG) criteria supporting a clinical RBD diagnosis. We quantitatively evaluated EMG activity and investigated its overnight distribution in patients with isolated qualitative RWA.Fifty participants with an incidental polysomnographic finding of RWA (isolated qualitative RWA) were included. Tonic, phasic, and ‘any’ EMG activity during REM sleep on PSG were quantified retrospectively.Referring to the quantitative cut-off values for a polysomnographic diagnosis of RBD, 7/50 (14%) and 6/50 (12%) of the patients showed phasic and ‘any’ EMG activity in the mentalis muscle above the respective cut-off values. No patient was above the cut-off value for tonic EMG activity or phasic EMG activity in the anterior tibialis muscles. Patients with RWA above the cut-off value showed higher amounts of RWA during later REM sleep periods.This is the first study showing that some subjects with incidental RWA meet the refined quantitative EMG criteria for a diagnosis of RBD. Future longitudinal studies must investigate whether this subgroup with isolated qualitative RWA is at an increased risk of developing fully expressed RBD and/or neurodegenerative disease.

Loss of REM sleep features across nighttime in REM sleep behavior disorder

ObjectivesMelatonin is a chronobiotic treatment which also alleviates rapid eye movement (REM) sleep behavior disorder (RBD). Because the mechanisms of this benefit are unclear, we evaluated the clock-dependent REM sleep characteristics in patients with RBD, whether idiopathic (iRBD) or associated with Parkinson's Disease (PD), and we compared findings with PD patients without RBD and with healthy subjects. MethodsAn overnight videopolysomnography was performed in ten iRBD patients, ten PD patients with RBD (PD + RBD+), ten PD patients without RBD (PD + RBD−), and ten controls. The rapid eye movement frequency per minute (REMs index), the tonic and phasic electromyographic (EMG) activity of the levator menti muscle, and the duration of each REM sleep episode were evaluated. A generalized linear model was applied in each group, with the REM sleep cycle (four ordinal levels) as the dependent variable, as a function of REMs index, REM sleep duration, and tonic and phasic EMG activity. ResultsFrom the first to the fourth sleep cycle, REM sleep duration progressively increased in controls only, REMs index increased in subjects without RBD but not in patients with RBD, whether idiopathic or associated with PD, whereas tonic and phasic EMG activity did not change. ConclusionsPatients with PD or iRBD lost the physiologic nocturnal increase in REM sleep duration, and patients with RBD (either with or without PD) lost the increase of REMs frequency across the night, suggesting an alteration in the circadian system in RBD. This supports the hypothesis of a direct effect of melatonin on RBD symptoms by its chronobiotic activity.

Quantitative assessment of isolated rapid eye movement (REM) sleep without atonia without clinical REM sleep behavior disorder: clinical and research implications

BackgroundRapid eye movement (REM) sleep without atonia (RWA) is observed in some patients without a clinical history of REM sleep behavior disorder (RBD). It remains unknown whether these patients meet the refined quantitative electromyographic (EMG) criteria supporting a clinical RBD diagnosis. We quantitatively evaluated EMG activity and investigated its overnight distribution in patients with isolated qualitative RWA. MethodsFifty participants with an incidental polysomnographic finding of RWA (isolated qualitative RWA) were included. Tonic, phasic, and ‘any’ EMG activity during REM sleep on PSG were quantified retrospectively. ResultsReferring to the quantitative cut-off values for a polysomnographic diagnosis of RBD, 7/50 (14%) and 6/50 (12%) of the patients showed phasic and ‘any’ EMG activity in the mentalis muscle above the respective cut-off values. No patient was above the cut-off value for tonic EMG activity or phasic EMG activity in the anterior tibialis muscles. Patients with RWA above the cut-off value showed higher amounts of RWA during later REM sleep periods. ConclusionsThis is the first study showing that some subjects with incidental RWA meet the refined quantitative EMG criteria for a diagnosis of RBD. Future longitudinal studies must investigate whether this subgroup with isolated qualitative RWA is at an increased risk of developing fully expressed RBD and/or neurodegenerative disease.

Motor Events during Healthy Sleep: A Quantitative Polysomnographic Study

Many sleep disorders are characterized by increased motor activity during sleep. In contrast, studies on motor activity during physiological sleep are largely lacking. We quantitatively investigated a large range of motor phenomena during polysomnography in physiological sleep. Prospective polysomnographic investigation. Academic referral sleep laboratory. One hundred healthy sleepers age 19-77 y were strictly selected from a representative population sample by a two-step screening procedure. N/A. Polysomnography according to American Academy of Sleep Medicine (AASM) standards was performed, and quantitative normative values were established for periodic limb movements in sleep (PLMS), high frequency leg movements (HFLM), fragmentary myoclonus (FM), neck myoclonus (NM), and rapid eye movement (REM)-related electromyographic (EMG) activity. Thirty-six subjects had a PLMS index > 5/h, 18 had a PLMS index > 15/h (90th percentile: 24.8/h). Thirty-three subjects had HFLM (90th percentile: four sequences/night). All subjects had FM (90th percentile 143.7/h sleep). Nine subjects fulfilled AASM criteria for excessive FM. Thirty-five subjects had NM (90th percentile: 8.8/h REM sleep). For REM sleep, different EMG activity measures for the mentalis and flexor digitorum superficialis muscles were calculated: the 90th percentile for phasic mentalis EMG activity for 30-sec epochs according to AASM recommendation was 15.6%, and for tonic mentalis EMG activity 2.6%. Twenty-five subjects exceeded the recently proposed phasic mentalis cutoff of 11%. None of the subjects exceeded the tonic mentalis cutoff of 9.6%. Quantification of motor phenomena is a basic prerequisite to develop normative values, and is a first step toward a more precise description of the various motor phenomena present during sleep. Because rates of motor events were unexpectedly high even in physiological sleep, the future use of normative values for both research and clinical routine is essential.

Wavelet analysis for detection of phasic electromyographic activity in sleep: Influence of mother wavelet and dimensionality reduction

Phasic electromyographic (EMG) activity during sleep is characterized by brief muscle twitches (duration 100–500ms, amplitude four times background activity). High rates of such activity may have clinical relevance. This paper presents wavelet (WT) analyses to detect phasic EMG, examining both Symlet and Daubechies approaches. Feature extraction included 1s epoch processing with 24 WT-based features and dimensionality reduction involved comparing two techniques: principal component analysis and a feature/variable selection algorithm. Classification was conducted using a linear classifier. Valid automated detection was obtained in comparison to expert human judgment with high (>90%) classification performance for 11/12 datasets.

Normative EMG Values during REM Sleep for the Diagnosis of REM Sleep Behavior Disorder

Correct diagnosis of rapid eye movement sleep behavior disorder (RBD) is important because it can be the first manifestation of a neurodegenerative disease, it may lead to serious injury, and it is a well-treatable disorder. We evaluated the electromyographic (EMG) activity in the Sleep Innsbruck Barcelona (SINBAR) montage (mentalis, flexor digitorum superficialis, extensor digitorum brevis) and other muscles to obtain normative values for the correct diagnosis of RBD for clinical practice. Two university hospital sleep disorder centers. Thirty RBD patients (15 idiopathic [iRBD], 15 with Parkinson disease [PD]) and 30 matched controls recruited from patients with effectively treated sleep related breathing disorders. Not applicable. Participants underwent video-polysomnography, including registration of 11 body muscles. Tonic, phasic, and "any" (any type of EMG activity, irrespective of whether it consisted of tonic, phasic or a combination of both) EMG activity was blindly quantified for each muscle. When choosing a specificity of 100%, the 3-sec miniepoch cutoff for a diagnosis of RBD was 18% for "any" EMG activity in the mentalis muscle (area under the curve [AUC] 0.990). Discriminative power was higher in upper limb (100% specificity, AUC 0.987-9.997) than in lower limb muscles (100% specificity, AUC 0.813-0.852). The combination of "any" EMG activity in the mentalis muscle with both phasic flexor digitorum superficialis muscles yielded a cutoff of 32% (AUC 0.998) for patients with iRBD and with PD-RBD. For the diagnosis of iRBD and RBD associated with PD, we recommend a polysomnographic montage quantifying "any" (any type of EMG activity, irrespective of whether it consisted of tonic, phasic or a combination of both) EMG activity in the mentalis muscle and phasic EMG activity in the right and left flexor digitorum superficialis muscles in the upper limbs with a cutoff of 32%, when using 3-sec miniepochs.

Usefulness of the SINBAR electromyographic montage to detect the motor and vocal manifestations occurring in REM sleep behavior disorder

Objective In a previous study we showed that simultaneous electromyographic (EMG) recording of the mentalis, flexor digitorum superficialis and extensor digitorum brevis (SINBAR EMG montage) detected the highest rates of rapid eye movement (REM) sleep phasic EMG activity in subjects with REM sleep behavior disorder (RBD). As a next step, in the present study we evaluated the usefulness of the SINBAR EMG montage to detect the movements and vocalizations occurring in RBD. Methods Polysomnographic studies with synchronized audiovisual monitoring of 11 patients with idiopathic RBD were analyzed. Phasic EMG activity in REM sleep was scored and quantified in 3-s mini-epochs while the video was reviewed to detect motor events and vocalizations. Results A total of 64.8% (11,562 out of 17,848) of all mini-epochs contained phasic EMG activity, whereas 28.8% (5135 out of 17,848) contained movements or vocalizations. Using the SINBAR EMG montage, 94.4% of the mini-epochs containing behavioral events were linked to phasic EMG activity. The sensitivity of the SINBAR EMG montage was 94.4%, specificity was 47.2%, negative predictive value was 95.4% and positive predictive value was 41.9%. Isolated EMG recording of the mentalis did not show phasic EMG activity in 35.5% of the behavioral events seen in the video. Conclusions The SINBAR EMG montage is a useful approach for the diagnosis of RBD showing that simultaneous EMG recording of the mentalis, flexor digitorum superficialis and extensor digitorum brevis muscles detected the majority (94.4%) of the motor and vocal manifestations occurring in RBD. For clinical purposes, this means that it is efficient to screen the video when increased phasic EMG activity is seen on the polysomnography.

The investigation of locomotor activity control system in humans under the air-stepping conditions during passive and voluntary leg movements

The degree of activation of the central stepping program during passive leg movement was studied in healthy subjects under unloading conditions; the excitability of spinal motoneurons was studied during passive and voluntary stepping movements. Passive stepping movements with characteristics maximally close to those during voluntary stepping were accomplished by the experimenter. The bursts of muscular activity during voluntary and imposed stepping movements were compared. In addition, the influence on the leg movement of artificially created loading onto the foot was studied. The excitability of spinal motoneurons was estimated by the amplitude of modulation of the m. soleus H reflex. Changes in the H reflex (Hoffmann’s reflex) after fixation of the knee and hip joints were also studied. In most subjects, passive movements were accompanied by bursts of electromyographic (EMG) activity in the hip muscles (sometimes in shank muscles); the timing of the EMG burst during the step cycle coincided with the burst’s timing during voluntary stepping. In many cases, the bursts in EMG activity exceeded the activity of homonymous muscles during voluntary stepping. Simulation of foot loading influenced significantly the distal part of the moving extremity during both voluntary and passive movements, which was expressed in the appearance of movements in the ankle joint and an increase in the phasic EMG activity of the shank muscles. The excitability of motoneurons during passive movements was higher than during voluntary movements. Changes and modulation of the H reflex throughout the step cycle were similar without restriction of joint mobility and without hip joint mobility. Fixation of the knee joint was of great importance. It is supposed that imposed movements activate the same mechanisms of rhythm generation as supraspinal commands during voluntary movements. During passive movements, presynaptic inhibition depends mostly on the afferent influences from the moving leg rather than on the central commands. Under the conditions of “air-stepping,” the afferent influences from the foot pressure receptors are likely to interact actively with the central program of stepping and to determine the final activity pattern irrespective of the movement type (voluntary or passive).

Hypertonia in childhood secondary dystonia due to cerebral palsy is associated with reflex muscle activation

It is often assumed that co-contraction of antagonist muscles is responsible for increased resistance to passive movement in hypertonic dystonia. Although co-contraction may certainly contribute to hypertonia in some patients, the role of reflex activation has never been investigated. We measured joint torque and surface electromyographic activity during passive flexion and extension movements of the elbow in 8 children with hypertonic arm dystonia due to dyskinetic cerebral palsy. In all cases, we found significant phasic electromyographic activity in the lengthening muscle, consistent with reflex activity. By correlating activation with position or velocity of the limb, we determined that some children exhibit position-dependent activation, some exhibit velocity-dependent activation, and some exhibit a mixed pattern of activation. We conclude that involuntary or reflex muscle activation in response to stretch may be a significant contributor to increased tone in hypertonic dystonia, and we conjecture that this activation may be more important than co-contraction for determining the resistance to passive movement.

Quantification of electromyographic activity during REM sleep in multiple muscles in REM sleep behavior disorder.

The aim of our study was to determine which muscle or combination of muscles (either axial or limb muscles, lower or upper limb muscles, or proximal or distal limb muscles) provides the highest rates of rapid eye movement (REM) sleep phasic electromyographic (EMG) activity seen in patients with REM sleep behavior disorder (RBD). Two university hospital sleep disorders centers. Seventeen patients with idiopathic RBD (n = 8) and RBD secondary to Parkinson disease (n = 9). Not applicable. Patients underwent polysomnography, including EMG recording of 13 different muscles. Phasic EMG activity in REM sleep was quantified for each muscle separately. A mean of 1459.6 +/- 613.8 three-second REM sleep mini-epochs were scored per patient. Mean percentages of phasic EMG activity were mentalis (42 +/- 19), flexor digitorum superficialis (29 +/- 13), extensor digitorum brevis (23 +/- 12), abductor pollicis brevis (22 +/- 11), sternocleidomastoid (22 +/- 12), deltoid (19 +/- 11), biceps brachii (19 +/- 11), gastrocnemius (18 +/- 9), tibialis anterior (right, 17 +/- 12; left, 16 +/- 10), rectus femoris (left, 11 +/- 6; right, 9 +/- 6), and thoraco-lumbar paraspinal muscles (6 +/- 5). The mentalis muscle provided significantly higher rates of excessive phasic EMG activity than all other muscles but only detected 55% of all the mini-epochs with phasic EMG activity. Simultaneous recording of the mentalis, flexor digitorum superficialis, and extensor digitorum brevis muscles detected 82% of all mini-epochs containing phasic EMG activity. This combination provided higher rates of EMG activity than any other 3-muscle combination. Excessive phasic EMG activity was more frequent in distal than in proximal muscles, both in upper and lower limbs. Simultaneous recording of the mentalis, flexor digitorum superficialis, and extensor digitorum brevis muscles provided the highest rates of REM sleep phasic EMG activity in subjects with RBD.

A Taxonomic Analysis of Sleep Stages

To study the structure of human sleep at the level of sleep stages. We applied taxonomic statistics to detect significant configurations (types) of different physiologic variables and their relationship to sleep stages. DESIGN AND STATISTICS: Polygraphic sleep recordings from 32 subjects (normal sleepers as well as patients with insomnia, sleep apnea, or narcolepsy; n = 8 per group) were visually scored and submitted to a configural frequency analysis. The configural frequency analysis was computed with 3 continuous input variables: an electroencephalogram parameter, which represents the point of gravity of the EEG frequency distribution; the alpha slow-wave index, and the Rest Index, based on the presence or absence of phasic electromyographic activity. These variables were dichotomized for further analysis. The combination of 2 levels ( + or -) and 3 variables resulted in 2(3) patterns ( +++ to - - - ). The configural frequency analysis is a nonparametric X2-type multivariate statistic that identifies significant patterns or types. Each sleep stage contained 3 or 4 types. For non-rapid eye movement sleep stages 2, 3, and 4, types overlapped, whereas there was no overlap of types between stages 1 and 2. Types of rapid eye movement sleep did not overlap with those from stages 2, 3, and 4 but did overlap with wake and stage 1 types. The majority of observed types were significant in all 4 groups of subjects. Sleep stages appear to be less homogenous than rule-based sleep scoring would suggest. Types were either restricted to one stage or overlapped with neighboring stages.

Quantification of Electromyographic Activity During Sleep: A Phasic Electromyographic Metric

Recording of electromyographic (EMG) activity is considered essential for defining rapid eye movement (REM) sleep and for quantifying certain types of movements in sleep, such as periodic leg movements in sleep (PLMS). However, routine analyses of EMG activity beyond such purposes is performed rarely and quantified seldom, and normative data are lacking. In this study, the authors examined systematic application of a visual scoring system for short-duration (approximately 100-millisecond) phasic EMG activity recorded from five different muscle groups (submentalis, left/right anterior tibialis, left/right brachioradialis) recorded from two different age groups of normal subjects and a group of patients with Parkinson's disease. Quantification of this activity was labeled as a phasic electromyographic metric (PEM). PEM data were compiled separately by REM and non-REM sleep. Results indicated that PEM is a normal part of REM sleep in all muscle groups, more specifically constituting about 5% (SD = 3.1%) of 2.5-second intervals of REM sleep in the mentalis in healthy young adults. It occurs at higher rates in patients with Parkinson's disease, and its quantification in the legs may be influenced to some degree by the presence of PLMS. PEM may be a useful metric amenable to quantification with digital techniques. It may have particular relevance for the identification of neurodegenerative conditions in which disinhibition of midbrain dopaminergic pathways results in excessive motor discharge during sleep.

Effects of unilateral and bilateral labyrinthectomy on rat postural muscle properties: the soleus

The aim of our study was to determine whether the suppression of the vestibular inputs could have effects on the soleus muscle properties similar to the modifications observed after an episode of microgravity. The inner ear lesion was performed by surgical labyrinthectomy. Twenty-nine male Wistar rats were used for this study and were divided into three experimental groups: control (CONT, n = 7), unilateral labyrinthectomized (UL, n = 14) and bilateral labyrinthectomized (BL, n = 8). Mechanical, histochemical and electrophoretic parameters were determined 17 days after the operation. Furthermore, electromyographic (EMG) activity of the soleus muscle was examined at 1 h, 1 day and 17 days. Our results showed that UL and BL groups did not present any sign of muscle atrophy when compared to CONT group. However, the contractile and phenotypical characteristics of UL and BL soleus muscles revealed that the muscle evolved from slow toward a slower type. This transition was correlated with a more tonic EMG activity pattern. To conclude, our data demonstrated that soleus muscle transformations observed after microgravity (muscle atrophy, slow-to-fast transition, phasic EMG activity) were not directly the consequence of a vestibular silence.

Auditory startle response in cervical dystonia.

The excitability of brainstem neurons is abnormally enhanced in patients with cervical dystonia (CD), but the extend of such abnormality is not known. We examined whether patients with CD showed abnormalities in the auditory startle response (ASR), a brainstem reflex elicited by an unexpected loud stimulus. Thirteen patients with CD were investigated 3 months after botulinum toxin treatment. Thirteen healthy volunteers served as controls. ASRs were elicited by binaural high-intensity auditory stimuli. Reflex electromyographic (EMG) activity was recorded simultaneously with surface electrodes bilaterally from masseter, orbicularis oculi, sternocleidomastoid, and biceps brachii muscles. We found that ASR onset latencies were similar for patients and controls. CD patients had significantly lower ASR probabilities than controls (P = 0.007). ASR area under the curve was significantly smaller in CD patients (P = 0.017). Similar to controls, patients showed a significant habituation of ASR (P < 0.001, each); however, CD patients showed a prolonged tonic or phasic EMG activity after the initial ASR that was not observed in controls. Normal latencies and recruitment pattern indicate a preserved organization of intrinsic neural pathways mediating ASR in CD. Reduced ASR probability and magnitude as well as prolonged EMG activity after the proper startle response corroborate and extend previous findings on brainstem dysfunction in CD.

Invariability of the privileged direction of the maximal EMG activity during speed-related activation for reaching in the vertical plane

Spatial tuning of goal-directed movements is a critical phenomenon for the central nervous system. The use of reliable models is a necessary step for the understanding of the neural mechanisms governing reaching movements. We analysed phasic electromyographic (EMG) activities associated with upper limb reaching movements in the vertical plane (12 targets) in seven healthy subjects during three successive sessions.We tested the hypothesis that one of the fundamental parameters of the directional tuning of phasic EMG activities is the peak of EMG activity. To characterize the tuning of phasic EMG activities for the seven recorded muscles (brachioradialis, biceps, medial and long head of triceps, anterior and posterior deltoid, latissimus dorsi), we digitally compressed the EMG activities corresponding to slow reaches to the same targets into the time frame of the fast EMG traces. Estimates of gravity-related components were subtracted. Peak of EMG activities in the resulting phasic traces were identified for each muscle and each target. The maximal peak EMG amongst the 12 peaks of EMG activity in the sagittal plane was called M Peak EMG. We defined the directional dominance as the ratio of the M Peak EMG divided by the Peak EMG in the opposite direction. The M Peak EMG for each muscle was always found in the same privileged direction of the movement, except for the latissimus dorsi. The directional dominance remained unchanged across recording sessions for the brachioradialis, anterior deltoid and posterior deltoid. However, the directional dominance increased across sessions for the biceps, medial head of triceps, long head of triceps and latissimus dorsi. The invariability of the privileged direction of the M peak EMG was thus observed for six of the seven muscles investigated. Therefore, we suggest that the selection of the privileged direction of the M Peak EMG represents a robust parameter to study the neuromuscular control strategy underlying the specification of movement direction.

Decreased phasic EMG activity during rapid eye movement sleep in treatment-naïve Parkinson's disease: effects of treatment with levodopa and progression of illness.

Rapid eye movement (REM) sleep behavior disorder (RBD) is frequently associated with Parkinson's disease (PD) and may anticipate its diagnosis by several years. We assessed the presence of motor dyscontrol during REM sleep in treatment-naïve PD patients and investigated the putative effect of levodopa (L-dopa) treatment on motor activity. Overnight sleep studies were performed on 15 previously untreated PD patients and 14 controls at baseline, again after a 3- to 9-month treatment period with a low dose of L-dopa, and 2 to 5 days after treatment discontinuation (in 8 patients). No differences in sleep parameters were observed across groups or treatment conditions. None of the patients met criteria for RBD at baseline, whereas 5 patients were symptomatic at the time of the second sleep study. A quantitative analysis of electromyographic (EMG) activity during REM sleep showed a lower phasic twitching activity in untreated PD than in controls. However, an increase in both phasic twitching and tonic activity was found after treatment with L-dopa. Discontinuation of treatment resulted in a return to pretreatment values of phasic but not of tonic EMG activity. Thus, the increase in phasic activity seems to depend on the effects of L-dopa, whereas the increase in tonic EMG activity during REM sleep might be caused by other factors such as the progression of disease. Potential implications for the understanding of the relationship between RBD and PD are discussed.

Relationship between cocontraction, movement kinematics and phasic muscle activity in single-joint arm movement

Patterns of muscle coactivation provide a window into mechanisms of limb stabilization. In the present paper we have examined muscle coactivation in single-joint elbow and single-joint shoulder movements and explored its relationship to movement velocity and amplitude, as well as phasic muscle activation patterns. Movements were produced at several speeds and different amplitudes, and muscle activity and movement kinematics were recorded. Tonic levels of electromyographic (EMG) activity following movement provided a measure of muscle cocontraction. It was found that coactivation following movement increased with maximum joint velocity at each of two amplitudes. Phasic EMG activity in agonist and antagonist muscles showed a similar correlation that was observable even during the first 30 ms of muscle activation. All subjects but one showed statistically significant correlations on a trial-by-trial basis between tonic and phasic activity levels, including the phasic activity measure taken at the initiation of movement. Our findings provide direct evidence that muscle coactivation varies with movement velocity. The data also suggest that cocontraction is linked in a simple manner to phasic muscle activity. The similarity in the patterns of tonic and phasic activation suggests that the nervous system may use a simple strategy to adjust coactivation and presumably limb impedance in association with changes in movement speed. Moreover, since the pattern of tonic activity varies with the first 30 ms of phasic activity, the control of cocontraction may be established prior to movement onset.

Response of the canine internal intercostal muscles to chest wall vibration.

Although high-frequency mechanical vibration of the rib cage reduces dyspnea, its effects on the respiratory muscles are largely unknown. We have previously shown that in anesthetized dogs, vibrating the rib cage during inspiration elicits a marked increase in the inspiratory electromyographic (EMG) activity recorded from the external intercostal muscles but does not affect tidal volume (VT). In the present studies, we have tested the hypothesis that the maintenance of VT results from the concomitant contraction of the internal interosseous (expiratory) intercostals. When the rib cage was vibrated (40 Hz) during hyperventilation-induced apnea, a prominent activity was recorded from the external intercostals but no activity was recorded from the internal intercostals, including when the muscles were lengthened by passive inflation. The internal intercostals remained also silent when vibration was applied during spontaneous inspiration, and the phasic expiratory EMG activity recorded from them was unaltered when vibration was applied during expiration. Thus, the internal interosseous intercostals in dogs are much less sensitive to vibration than the external intercostals, and they do not interfere with the action of these latter during rib cage vibration. This lack of sensitivity might be the result of a reflex inhibition of the muscle spindle afferents by afferents from external intercostal muscle spindles.

Role of the superior pharyngeal constrictor muscle in forced breathing in dogs.

Respiratory-related electromyographic (EMG) activity of the superior pharyngeal constrictor (SPC) muscle was analyzed during the early stage of forced breathing. Four adult dogs anesthetized with sodium pentobarbital were used. In the first part of the study, oral and nasal breathing tubes were placed into the respective cavities, and a tracheotomy tube was placed in the second part of the study. Two conditions, the presence (oral-nasal tube breathing) and absence (tracheotomy breathing) of airflow in the upper airway, were achieved in each dog. Following quiet breathing, animals were connected to a closed breathing system, first by an oral-nasal tube and then by a tracheotomy tube. We proposed to induce a forced breathing condition mechanically by using this system for 1 minute. We increased resistance to airflow during forced breathing by means of connecting tubes and a bag. Our aim was not to produce chemical drive but to produce a forced respiration by increasing the resistance to airflow. Tidal volume, breathing frequency, minute volume, chest wall movement, and EMG activity of the SPC muscle were measured and analyzed. During quiet breathing through an oral-nasal or tracheotomy tube, low-amplitude EMG activity of the SPC muscle corresponding to the expiratory cycle of the respiration was observed. In both study conditions, phasic expiratory EMG activity increased immediately after the advent of the breathing from the closed system. Tidal volumes and frequencies also increased rapidly during forced breathing. An increase in the resistance to airflow increased the activity of the SPC muscle. This augmented respiratory activity probably assists the patency of the upper airway. The augmented respiratory activity was independent of the local reflex pathways. Respiratory-related activity of the SPC muscle may help dilate and stiffen the pharyngeal airway, promoting airway patency.