Histamine induced airway response in pre-school children assessed by a non-invasive EMG technique

The aim of the study was to investigate the association between surface electromyographic (EMG) activity of the diaphragm and intercostal muscles, and clinical symptoms (wheeze, cough, increased respiratory rate and prolonged expiration) during bronchial challenge testing and after administration of salbutamol in asthmatic pre-school children. A histamine challenge test was performed in 20 asthmatic pre-school children. The histamine dose at the appearance of 1 or more clinical symptoms was defined as the maximum histamine provocation dose (PDcs). The clinical symptoms were recorded with a microphone over the trachea. The logarithm of the EMG-Activity-Ratio (log EMGAR; mean peak activity ratio to baseline of respiratory muscles during tidal breathing) was used as EMG parameter. In both the diaphragmatic and the intercostal log EMGAR values a linear increase was observed in the four histamine dose-steps prior to PDcs. At PDcs the mean log EMGAR of the diaphragm (di) and intercostal muscles (int) was significantly increased as compared to the baseline values. After administration of salbutamol the log EMGARdi and log EMGARint returned to baseline values and the clinical symptoms normalized in all children. At PDcs, no significant differences in the log EMGAR values could be detected at the appearance of the distinctive clinical symptoms, which suggests that wheezing is not the only indicator for the detection of airway responsiveness in young children. We found a linear association between histamine dose and the increase in surface diaphragmatic and intercostal respiratory EMG activity during a bronchial challenge test in pre-school asthmatic children, which returned to baseline values after inhalation of salbutamol. These findings support the idea that EMG measurements of the diaphragm and intercostal muscles may offer an opportunity to estimate airway response in young children in an alternative way.