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 an d intercostal muscles. The purpose of this study was to evaluate the reprod ucibility of the EMG measurements. Eleven adults, 39 school children (20 he althy, 19 asthmatic), and 16 preschool children were studied during tidal b reathing 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 electrode s 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 electro de pairs were placed on the rectus abdominis muscle. A newly designed digit al 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 describe d the agreement between the repeated measurements within the same subjects. No significant differences were found between the measurements on the sepa rate occasions. Our observations indicate that the EMG signals derived from the diaphragm and intercostal muscles are, in different age groups with an d without asthma, reproducible during tidal breathing.