Differential neuromuscular effects of vecuronium on the adductor and abductor laryngeal muscles and tibialis anterior muscle in dogs.

We have studied in dogs the neuromuscular blocking effects of vecuronium on the cricothyroid (CT) (a tensor muscle of the vocal folds) and posterior cricoarytenoid (PCA) (sole abductor muscle of the vocal folds) muscles of the larynx and the tibialis anterior (TA) muscle. The lungs of the animals were ventilated mechanically with 0.2% halothane and oxygen. Electromyography (EMG) was performed on the CT, PCA and TA muscles by inserting fine wire electrodes. The evoked compound EMG responses of the three muscles were measured simultaneously in an identical manner by stimulating supramaximally the superior laryngeal, recurrent and sciatic nerves at 0.1 Hz and 0.2 ms. Vecuronium was infused continuously at a rate of 0.01 mg kg-1 min-1 for 8 min. Vecuronium produced more intense neuromuscular block in the CT than in the PCA and TA muscles. The rate of recovery was significantly slowly in the CT compared with the PCA and TA muscles. This study confirms the difference in sensitivity between laryngeal and peripheral muscles, demonstrating that the intrinsic laryngeal muscles do not all behave similarly after administration of vecuronium.