Changes in neural drive (EMGd) and neuromuscular coupling during histamine-induced bronchoconstriction in patients with asthma.

This study was undertaken in order to assess the neural drive to the respiratory muscles and the inspiratory neuromuscular coupling in patients with bronchial asthma during histamine-induced bronchoconstriction. Bronchoconstriction was produced in a graded fashion, with histamine phosphate aerosol of increasing dose, in twelve asymptomatic asthmatic patients and was measured by FEV1. Inspiratory drive was measured by electromyographic activity of the diaphragm (EMGd) and the coupling of the neural drive to the respiratory muscles was assessed by the relationship of mouth occlusion pressure (P0.1) to EMGd. During the test we also measured electromyographic activity of the inspiratory intercostal (EMGint), sternomastoid (EMGsm) and expiratory abdominal (EMGab) muscles. Histamine caused a significant decrease in FEV1, a significant increase in P0.1, EMGd, EMGint, and a relevant increase in EMGsm, with no substantial increase in EMGab. An inverse significant relationship between the change in FEV1 and changes in P0.1, EMGd and EMGint and a significant correlation between the change in FEV1 and in the P0.1/EMGd ratio were observed. We conclude that a progressive increase in bronchospasm is accompanied by a progressive increase in respiratory neural drive and decrease in neuromuscular coupling. This could be caused both by an increase in lung volume and a lack of abdominal expiratory muscle recruitment.