Using the wedged bronchoscope technique to measure collateral resistance (Rcs), we evaluated the effect of succinylcholine (SCh) on the response to acetylcholine (ACh) and methacholine (MCh) in the lung periphery in six mongrel dogs. Dogs were anesthetized, intubated, and mechanically ventilated. After a stable baseline Rcs was obtained, responses to intravenous ACh (25-200 μg), intravenous MCh (3-30 μg), and aerosolized ACh (30-100 μg/ml for 15 s) were measured. We compared the Rcs responses with 1) ACh alone, 2) ACh 2 min after SCh (0.5 mg/kg), 3) ACh 2 min after SCh and during hexamethonium infusion (5 mg/kg + 10 mg·kg-1·h-1), 4) MCh 2 min after SCh, and 5) ACh aerosol 2 min after SCh. SCh did not significantly alter baseline airway tone. SCh increased the Rcs response to ACh by 48 ± 17% (SE) (P < 0.01). SCh in the presence of hexamethonium increased the Rcs response by 10 ± 3% (P < 0.05), while hexamethonium itself increased the response to ACh by 69 ± 27%. Because SCh did not increase the Rcs response to intravenous MCh or to aerosolized ACh, SCh probably enhances airway reactivity to intravenous ACh by competing for pseudocholinesterase in plasma. We conclude that the level of muscle relaxant must be taken into account in interpreting studies of airway reactivity when intravenous ACh is employed.
- airway reactivity
- collateral resistance
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation