A literature review of the methodology of EMG recordings of the diaphragm.

INTRODUCTION: EMG measurements of the diaphragm (rEMG) provide insight in to ventilatory muscle activity. Applicability of these measurements has improved, but literature of the different rEMG measurement techniques is inconsistent. This makes it difficult to compare studies of rEMG technique. This study summarizes the current available literature on rEMG and focuses on the validation of the techniques. Furthermore, we propose to use validation criteria to improve the quality, for further research. METHODS: Pubmed, Ovid Medline and EMBASE were searched for studies describing rEMG experiments with transcutaneous (tc-rEMG) and/or transesophageal (te-rEMG) methods.Validation criteria included feasibility, repeatability, signal disturbance and ECG gating. RESULTS: 650 studies were eligible for reviewing; 211 were excluded, and 39 articles described the measurement technique and were analyzed according to the criteria. 194 studies referred to another paper with a description of the technique and 206 failed to describe the technique nor had references to it. CONCLUSIONS: Many studies showed neither a description of the technique used, nor a validation of this technique. Others referred to studies that described the measurement technique. We propose that future studies on rEMG measurements at least meet the above mentioned criteria, in order to be able to compare study results.

Respiratory muscle activity and dyspnea during exercise in chronic obstructive pulmonary disease.

We aimed to determine by non-invasive EMG, whether during exercise: (1) COPD patients increase scalene and intercostal EMG activity, (2) increased EMG activity is associated with increased dyspnea, and (3) the ratio between EMG activity and volume displacement is increased in COPD compared to healthy subjects (HS). During a maximal incremental cycle test, scalene and intercostal EMG was derived transcutaneously in 17 COPD patients and 10 HS. Dyspnea was quantified using a Borg scale, ranging from zero to 10 (maximal dyspnea). For analyses the ratio between inspiratory muscle activity during exercise and activity during quiet breathing was used (logEMGAR). In COPD patients, scalene and intercostal activity increased at greater rate early in exercise compared to that of the HS. With a doubling of the logEMGAR, in COPD, dyspnea increased with 2.8/3.8 points, while in the HS, dyspnea increased less with 1.1/1.4 points. In COPD, there was a larger increase in EMG activity relatively to tidal volume increases.

Different breathing patterns in healthy and asthmatic children: responses to an arithmetic task.

UNLABELLED: Asthma patients have been reported to be sensitive to breathlessness, independent of the degree of airway obstruction. Paying attention and task performance may induce changes in breathing pattern and these in turn may mediate such a feeling. The present experiment investigates whether strained breathing induced by an arithmetic task was different in children with asthma compared to healthy children. METHODS: Seven healthy and eight asthmatic but symptom-free school children were equipped with electrodes for surface electromyographic (EMG) measurements of diaphragm, abdominal and intercostal (IC) muscles and with a strain gauge to monitor the pattern of breathing at rest and during an arithmetic task. The relative duration of exhalation and the relative speed of exhalation are used as measures of straining. The phase angle of maximal respiratory muscle activities relative to the maximal chest extension (MCE) are additional discriminating parameters. RESULTS: Asthmatic children breathed more slowly and already at rest the phase of their respiratory muscle activity appears to be different. While in healthy children the maximal activity of the (left)abdominal muscles occurred 5+/-29% later than the MCE, in children with asthma the maximal activity occurred 26+/-30% of the cycle earlier than MCE. In children with asthma the activity of the IC muscles starts weaning already at 10+/-30% before MCE, in contrast to the healthy children in which intercostal muscle weaning starts only at 1+/-24% after MCE. During arithmetic, the significant difference between the groups in this respect disappeared. CONCLUSION: Children with asthma show, even at rest, signs of respiratory muscle straining, probably in order to keep close control over the airflow in a similar way as healthy children during mental tasks. Such a 'careful' breathing pattern may work to prevent airway irritation also when they are free of symptoms.

Sciatic nerve transection in adult and young rats: abnormal EMG patterns during locomotion.

Transections of peripheral nerves usually lead to serious handicaps. In order to enhance insights into the poor functional recovery, we studied the effects of a unilateral sciatic nerve lesion in adult and young rats. Electromyographic (EMG) patterns of the tibialis anterior (a hindlimb flexor) and the gastrocnemius muscle (a hindlimb extensor) during walking were recorded after transecting the sciatic nerve at adult age and at the 10th postnatal day. After recovery periods lasting up to 21 weeks, EMG patterns in the hindleg muscles during locomotion were highly abnormal, irrespective of the age at lesioning. Electromyographic bursts were markedly irregular and, generally, coactivation of these antagonists was observed during walking. Other evidence has shown that after peripheral nerve transection, nerves randomly reinnervate their target muscles and we conclude that the patterns of muscle activity may be associated with the properties of foreign, as well as genuine, motor nerves. Behaviourally, walking patterns after a transection at adult age are markedly abnormal but, after transection at the 10th day, locomotion is much less disturbed. The finding of a discrepancy between a near normal walking pattern in rats operated on at a young age and severely disturbed EMG activity may be due to subtle readjustments in the force recruitment in the respective muscles, despite a random reinnervation by the sciatic nerve branches. These compensatory readjustments are particularly prominent after transection at an early age.

A new technique for simultaneously recording EMG and movements in experimental animals.

In this protocol a new system is presented for recording EMG signals from leg and trunk muscles along with video-recording of leg and trunk movements. The system comprises a front-end amplifier consisting of a reference amplifier, a differential amplifier with a filter combination and an analog to digital converter (ADC). A fiber optic transmitter connects the front end amplifier via a fiber cable to a receiver board placed in a personal computer (PC). A dedicated software programme (POLY) was written to process the physiological signals on the PC. The physiological recordings can be synchronized to video-recordings and the principles of this technique are given. The system allows to record artifact-free physiological signals and also to link activation patterns in muscles with kinematic aspects of movements.

Spontaneous motility in preterm infants treated with indomethacin.

OBJECTIVE: To determine in preterm infants with a patent ductus arteriosus (PDA) the effect of indomethacin treatment on spontaneous motor activity. STUDY DESIGN: Motor activity was assessed from repeated videotape recordings in 32 preterm infants (

Respiratory muscle activity measured with a noninvasive EMG technique: technical aspects and reproducibility.

A new method is being developed to investigate airway obstruction in young children by means of noninvasive electromyography (EMG) of diaphragmatic and intercostal muscles. The purpose of this study was to evaluate the reproducibility of the EMG measurements. Eleven adults, 39 school children (20 healthy, 19 asthmatic), and 16 preschool children were studied during tidal breathing on separate occasions: two for adults with a time interval of 3 wk and three for children with time intervals of 1 and 24 h. Single electrodes were placed on the second intercostal space left and right of the sternum and at the height of the frontal and the dorsal diaphragm. Bipolar electrode pairs were placed on the rectus abdominis muscle. A newly designed digital physiological amplifier without any analog filtering was used to measure the EMG signals. Except for the average dorsal diaphragm EMG derivation in healthy school children on the second occasion, a significant correlation between the mean peak-to-peak inspiratory activity of average diaphragmatic and intercostal EMG was found in the different age groups on the different measurement occasions (P < 0.05). To assess the repeatability, we described the agreement between the repeated measurements within the same subjects. No significant differences were found between the measurements on the separate occasions. Our observations indicate that the EMG signals derived from the diaphragm and intercostal muscles are, in different age groups with and without asthma, reproducible during tidal breathing.

Postural adjustments during spontaneous and goal-directed arm movements in the first half year of life.

We studied the development of postural control during goal-directed reaching and spontaneous arm movements in early infancy. Two groups of infants participated. The first group consisted of 10 healthy infants, who were assessed four times at the ages of 3, 4, 5 and 6 months. Each assessment consisted of simultaneous recording of video-data and surface EMGs of arm, neck, trunk, and leg muscles in various lying and sitting positions. Additionally, postural adjustments during spontaneous arm movements were studied in a second group of five infants aged 1-3 months. Already before the onset of successful reaching, which occurred at 4 5 months, both spontaneous and goal-directed arm movements were accompanied by a high amount of postural activity. During the goal-directed arm movements a preference for neck muscle activation and a direction specific organisation (dorsal postural muscles activated before the ventral antagonists) prevailed, whereas during spontaneous arm movements such a specific postural organisation was absent. With increasing age and concurrent with successful reaching, the amount of postural activity decreased. Still, the persisting postural activity continued to become more organised with increasing age. Position affected the postural adjustments accompanying goal-directed arm movements at all ages.

The development of postural adjustments during reaching in 6- to 18-month-old infants. Evidence for two transitions.

The present study focused on the developmental changes of postural adjustments accompanying reaching movements in healthy infants. We made a longitudinal study of ten infants between 6 and 18 months of age. During each session multiple surface electromyograms of arm, neck, trunk and leg muscles at the right side of the body were recorded during right-handed reaching movements in two positions ("upright sitting" in an infant chair and "long-leg" sitting without support). Simultaneously the whole session was recorded on video. Comparable data were present from the same infants at 3-5 months. Additionally, 18 infants (8-15 months) were assessed once during similar reaching tasks, but in these infants electromyographic activity of the trunk and neck muscles at both sides of the body were recorded. Our data revealed two transitions in the development of postural adjustments. The first transition was present around 6 months of age. At this age the postural muscles were infrequently activated during reaching movements. At 8 months ample postural activity reappeared and the infants developed the ability to adapt the postural adjustments to task-specific constraints such as arm movement velocity or the sitting position at the onset of the reaching movement. The second transition occurred between 12 and 15 months. Before 15 months the infants did not show consistent anticipatory postural activity, but from 15 months onwards they did, particularly in the neck muscles.

The activation of back muscles during locomotion in the developing rat.

The development of posture during locomotion was studied in rats from the 11th day until adulthood. The EMGs were recorded and analyzed of the left and right longissimus muscles at caudal, intermediate and rostral levels as well as of the gastrocnemius, the tibialis and the vastus medialis muscles and movements were simultaneously recorded on videotape. Results indicate that from the 12th day of life, burst activity occurs in the longissimus muscles which is phase-related to the stepcycle. Until the 21st day these muscles are most strongly activated during burst activity in the gastrocnemius muscle in the contralateral hindleg but thereafter this activation coincides with bursts in the ipsilateral gastrocnemius muscle. At adult age such activation in the LL is restricted to fast walking or to accelerations. Latencies between bursts in the longissimus muscles and the gastrocnemius muscles vary around 100 ms until the 25th day, but thereafter they decrease to adult values of less than 10 ms. The large variations in these phase-relations at all ages suggest that supraspinal influences and afferent input are important factors in this coupling. The shift from a contra- to an ipsilateral coupling between bursts in the longissimus and in the gastrocnemius muscles might indicate that an ontogenetically older pattern of locomotion with the trunk muscles playing a major role in propulsion, is replaced by a newer pattern, mainly effected by extremity movements.

Postural adjustments accompanying fast pointing movements in standing, sitting and lying adults.

The present study evaluated the effect of different positions, which varied in the amount of bodily support, on postural control during fast pointing movements. Fourteen adult subjects were studied in standing, various sitting and lying positions. Multiple surface electromyograms (EMGs) of arm, neck, trunk and upper leg muscles and kinematics were recorded during a standard series of unilateral arm movements. Two additional series, consisting of bilateral arm movements and unilateral arm movements with an additional weight, were performed to assess whether additional task-load affected postural adjustments differently in a sitting and standing position. Two pointing strategies were used--despite identical instructions. Seven subjects showed an elbow extension throughout the movements. They used the deltoid (DE) as the prime mover (DE group). The other seven subjects performed the movement with a slight elbow flexion and used the biceps brachii (BB) as the prime mover (BB group). The two strategies had a differential effect on the postural adjustments: postural activity was less and substantially later in the BB-group than in the DE group. Anticipatory postural muscle activity was only present in the DE group during stance. In all positions and task-load conditions the dorsal postural muscles were activated before their ventral antagonists. The activation rate, the timing and--to a lesser extent the amplitude of the dorsal muscle activity was position dependent. The position dependency was mainly found in the caudally located lumbar extensor (LE) and hamstrings (HAM) muscles. The EMG amplitude of LE and HAM was also affected by body geometry (trunk and pelvis position). Position and body geometry had only a minor effect on the activity of the neck and thoracic extensor muscles. This difference in behaviour of lower and upper postural muscles suggests that they could serve different postural tasks: the lower muscles being more involved in keeping the centre of mass within the limits of the support surface, and the upper ones in counteracting the reaction forces generated by movement onset. Increasing task-load by performing bilateral movements and--to a minor extent--during loaded unilateral movements affected the temporal and quantitative characteristics of the postural adjustments during standing and sitting in a similar way. The effect was present mainly during the early part of the response (within 100 ms after prime mover onset). This suggests that feedforward or anticipatory mechanisms play a major role in the task-specific modulation of postural adjustments.

Respiratory muscle activity in the assessment of bronchial responsiveness in asthmatic children.

We investigated whether an increase in transcutaneous electromyographic (EMG) activity of the diaphragm and intercostal muscles corresponds with the concentration of histamine that induces a 20% fall in the forced expiratory volume in one second (FEV1; PC20). Eleven asthmatic children (mean age 11.9 yr) were studied after they were given histamine challenge. EMG activity at PC20 or at the highest histamine concentration was compared with activity at baseline by calculating the ratio of the mean peak-to-peak excursion at the highest histamine dose to that at baseline [EMG activity ratio (EMGAR)]. In all children reaching PC20, an increase in diaphragmatic and intercostal EMGAR was observed. No increase was found at the dose step before PC20 was reached. In six challenges, no fall in FEV1 was induced, and no increase in EMGAR was seen. In two challenges, no fall in FEV1 was induced, but increase in diaphragmatic or intercostal EMGAR was observed. Increase in the electrical activity of the diaphragm and intercostal muscles in asthmatic children corresponds closely to a 20% fall in FEV1 induced by histamine challenge.

Assessment of general movements: towards a better understanding of a sensitive method to evaluate brain function in young infants.

The consistent presence of an abnormal quality of general movements (GMs) during the first postnatal months points to a high risk for the development of a neurological disability. To elucidate the significance of abnormal GMs during a single assessment, a classification system for abnormal GMs was developed. To this end six term and ten preterm infants with abnormal GMs were studied longitudinally with video and electromyographic (EMG) recordings till 59 weeks postmenstrual age (PMA). Two basic categories of abnormal GMs were distinguished: (1) mildly abnormal GMs (two types), which lacked fluency while conserving pattern complexity, and (2) definitely abnormal GMs (four types), which lacked fluency and complexity altogether. GM type before 39 weeks PMA correlated with findings on neonatal ultrasound brain scans. GM quality after 47 weeks PMA was strongly related to neurodevelopmental outcome at 1 1/2 years of age, suggesting that the absence of the age-specific 'fidgety' character of GMs could be a herald of disability.

The effect of behavioural state on general movements in healthy full-term newborns. A polymyographic study.

In a group a eight healthy full-term newborns 6-h polygraphic recordings, which included EMG recording of eight arm muscles, were made to investigate the effect of behavioural state on general movement (GM) organization. Simultaneous video recordings supplied information about the form of the GMs. Additionally the effect of non-nutritive sucking during State 4 was evaluated. Behavioural state had a distinct effect on the makeup of GMs. GMs during State 4 displayed best the fluency and elegance which are characteristic of normal GMs. State-1-GMs were rare, had a short duration and sometimes had an abrupt onset. During State 2 GMs had a fragmented appearance. EMG differences between GMs in State 2 and State 4 were demonstrated in burst duration (longer during State 2) and tonic background activity in the upper arm muscles (lower during State 2). Occasionally State-2-GMs had an abrupt onset. These abrupt GMs were less often preceded by rapid eye movements and heart rate changes than State-2-GMs with a gradual onset. GMs during State 5 were abrupt and vigorous and often had a high frequency tremor superimposed. The EMGs of State-5-GMs revealed a shorter interval between the EMG bursts and a higher EMG burst amplitude in the upper arm muscles than present during State-4-GMs. Non-nutritive sucking during State 4 induced a reduction of movement amplitude, a increase of EMG burst duration and an increase of tonic background activity in the biceps brachii and the extensor carpi muscles.

Developmental course of general movements in early infancy. II. EMG correlates.

In order to study developmental changes in muscle co-ordination during the first postnatal months, simultaneous polymyographic recordings and video-recordings were made during spontaneous movements of 22 healthy infants, who were followed from birth onwards. During the first 2 months general movements (GM) change from movements with a so-called 'writhing' character, which have a tight appearance, a relatively slow speed and a limited amplitude, into GM with a 'fidgety' character, which consist of an ongoing flow of small, elegant movements. We hypothesized that this transformation would coincide with a change from a pattern of co-contraction of antagonistic muscle groups into a pattern of reciprocal activation. This was not the case, a pattern of co-activation of antagonistic muscle groups remained the prevailing pattern. With increasing age, we found shorter burst durations of phasic activity, an attenuation of burst amplitude and a decrease of tonic background activity. These changes were attributed to a reduction of the sensitivity of the motor units due to spinal and supraspinal reorganization. It is hypothesized that the so-called 'bistable' properties of motoneurones play a central role in the observed phenomena: in neonates motor units are apt at displaying sustained activity, at 2 months of age the threshold for reaching this maintained activity increases, resulting in a low level of excitation of motor units during spontaneous movements. In the third month rapid arm movements ('swipes' and 'swats') develop. The 'swats' are characterized by a consistent pattern of reciprocal activity of antagonistic (shoulder) muscles.

Transcutaneous respiratory electromyographic monitoring.

The integrated diaphragm electromyogram (EMG) signal reflects function from the inspiratory centers to the neuromuscular junction. The feasibility and potential value of transcutaneous diaphragm electromyography (tcEMG) was confirmed in a group of infants using two prototype respiratory EMG monitors. Infants were monitored continuously for periods ranging from hours to days. One hundred were monitored for clinical reasons, looking for disordered respiratory behavior, while 47 were studied for technical/experimental reasons. Reliable measurements of diaphragm EMG activity were obtained, provided fully shielded electrode cables were used. Measurements in 28 ventilated infants and one adult confirmed that, unlike impedance and other non-electrophysiologic measures, tcEMG monitoring is not contaminated by ventilator-induced respiratory movements. The potential value of tcEMG monitoring in ventilated subjects is exemplified by illustrations of: diaphragmatic inactivity from phrenic nerve injury, inadequate central drive, and neuromuscular block; augmented expiratory muscle activity; and progressive increase in inspiratory diaphragmatic activity in the presence of a tension pneumothorax. TcEMG monitoring should prove a worthwhile addition to the available noninvasive respiratory monitoring techniques.

Respiratory muscle EMG in newborns: a non-intrusive method.

A non-intrusive method of recording the EMG of respiratory muscles with electronic suppression of the ECG artifact and averaging with a running window was employed in newborn infants at term to study respiratory patterns in different behavioural states. There are clear state-related differences in the diphragmatic and intercostal activity patterns. During most of the time in state 1 (quiet sleep) sustained tonic activity is found in the diaphragm as well as in intercostal muscles, but is virtually absent during state 2 (active sleep). During state 1 intercostal activity slightly precedes diaphragmatic activity whereas in state 2 both muscles contract about synchronously and vary widely in their amplitude. During periodic breathing the inspiratory EMG activity is absent in the pauses, but tonic activity may be present during periodic breathing in state 1. Isolated respiratory pauses with silence in the respiratory muscles occur in state 1 after sighs and starties with deep inspirations. During state 2 many respiratory pauses accompany gross movements and simultaneous laryngeal muscle activity suggests upper airway occlusion. Respiratory pauses without movements cannot be due to general alpha-motoneuron inhibition, because chin muscle activity may be seen at the same time. Gross movements often act as a reset mechanism for increase or decrease in tonic activity and phasic respiratory activity. Some speculations on the neural mechanisms of respiratory control based on the preliminary findings from the EMG recordings are mentioned.