Localization of bronchial response to ipratropium bromide by respiratory impedance measurement in asthmatics.

In 10 asthmatic subjects, the influence of 0.040 mg ipratropium bromide on impedance (Z) of the respiratory system (rs) was determined after cold air challenge. Cold air inhalation caused a significant increase of respiratory resistance (Rrs) at frequencies between 8 and 32 Hz. This increase of Rrs was more pronounced at lower frequencies and, therefore, Rrs became frequency dependent. Respiratory reactance (Xrs) decreased at all frequencies, resulting in an increase of resonant frequency. These changes were compatible with a peripheral airway obstruction and a decrease of airway compliance, according to Mead's analog of the respiratory system. Five min after inhalation of ipratropium bromide, a significant decrease of Rrs between 8 and 28 Hz and a significant increase of Xrs at all frequencies were observed, resulting in a decrease of resonant frequency. Ipratropium bromide significantly reversed the peripheral broncho-constriction induced by cold air challenge.