Hyperventilation during bronchial challenges in asthmatics: reproducibility and assessment of contributing factors.

Among asthmatics, the ventilatory response is heterogeneous during bronchial challenge. This study aimed to investigate the reproducibility of the response and to assess possible causes for hyperventilation. Repeated bronchial histamine and methacholine challenges (HiCh/MeCh) were performed in 10 asthmatic adolescents. Ventilation was monitored by respiratory inductive plethysmography (RIP), in order to minimally affect the spontaneous breathing pattern. FEV1 and the volume of trapped gas (measured as the volume of air mobilized by five maximal breaths after a multiple breath nitrogen washout to 2% N2), were used to assess mainly central and peripheral airways obstruction, respectively. When FEV1 had decreased by at least 20%, mean inspiratory flow (VTI/TI) increased by 21% and minute ventilation (V'I) by 21% and 23% during HiCh and MeCh, respectively (both P < 0.05). No correlation was found between the magnitude of the ventilatory response and either: the degree of FEV1 decline, the increase in gas trapping, SaO2 decline or the increase in dyspnoea score. Histamine challenge after beta 2-agonist pre-treatment was associated with increased ventilatory drive in one patient despite the absence of bronchial obstruction, indicating that histamine might directly stimulate afferent airway nerves which cause hyperventilation. The intra-individual variability of the ventilatory response (increase in V'I and VTI/TI) was more than 100% of the mean ventilatory response, while the variability of the bronchomotor response was about 25% of the mean bronchomotor response. Thus, during induced bronchial obstruction in asthmatics, the occurrence of hyperventilation and its intensity are not related to either the degree of central or peripheral airways obstruction, or to the degree of dyspnoea. The reproducibility of the ventilatory response is poor. The ventilatory response appears to be the result of a complex interaction between several afferent stimuli and central ventilatory control.