Previously, we1 have shown that peripheral resistance rises more in asthmatic subjects than in nonasthmatic subjects following direct stimulation with cool, dry air. To gain further insight into this response, we measured the input impedance (Z) of the lung periphery in response to methacholine by applying forced oscillations through a wedged bronchoscope in asthmatic and nonasthmatic subjects.
We used a computer-controlled piston pump (flexiVent; SCIREQ; Montreal, QU, Canada) to deliver a broad-band (ie, 0.5 to 20 Hz) oscillatory flow through the wedged bronchoscope during 8 s of apnea at functional residual capacity. Pressure at the tip of the bronchoscope and flow data were used to calculate Z. Z was measured at baseline, following escalating doses of methacholine, following three deep lung inflations (DIs), and, finally, following albuterol administration.