Electromyography of the Respiratory Muscles

Rationale. Electromyography can be used to assess the level and pattern of activation of the respiratory muscles.

Measurements. Surface electrodes have been used nearly exclusively for EMG recording of the respiratory muscles in infants and children. Surface electrodes are placed in the right sixth and seventh interspaces between the midaxillary and midclavicular lines for recording of diaphragmatic EMG (EMGdi) (69-71), in the second intercostal space parasternally for intercostal EMG recording, and at the midpoint between the umbilicus and iliac crest for abdominal muscle recording (71, 72). One study reported EMGdi using an esophageal electrode with specific equipment adapted for use in sleeping infants (73). No studies have been published using intramuscular electrodes for recording EMG of the respiratory muscles in infants or children.

Advantages. The recording of EMG of the respiratory muscles using surface electrodes is noninvasive.

Disadvantages. Surface electrode EMGdi tracings can be contaminated by other inspiratory or expiratory muscles (73). Therefore, when recording diaphragmatic EMG activity with surface electrodes, it is more appropriate to describe the values as chest wall EMG rather than EMGdi. Techniques to remove cardiac artifacts on the EMGdi have to take into account the high cardiac frequency in infants, especially in preterm infants (74) (see Artifacts in Section 3 of this Statement).

Normal values. Quantitative measurements of chest wall EMG recorded with surface electrodes have been reported for EMG time and frequency domains (69, 70, 74, 75). Few studies have described the activation of the respiratory muscles during quiet breathing in infants without respiratory disorders. in infants nursed in the supine position, phasic and tonic activity of the intercostal muscles have been reported during NREM sleep (69). contraction of the intercostal muscles stabilizes the highly compliant chest wall of the infant. The inter-

costal muscles are inhibited during REM sleep and chest wall distortion occurs during inspiration. No abdominal muscle activation has been reported in healthy infants nursed in the supine position during NREM sleep (71). Activation of abdominal muscles is observed during NREM sleep while breathing CO2, but not during REM sleep (71).

Clinical application. The main utility of recording of EMG of the respiratory muscles is during sleep studies. Persistent phasic chest wall EMG activity helps to identify obstructive respiratory events, especially obstructive hypopneas during sleep, and therefore should limit the use of the invasive measurement of Pes (76). EMG recording of abdominal muscles assesses the degree of abdominal muscle contraction in children with loaded breathing related to partial upper airway obstruction during sleep (71, 72).

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