TOPICAL ANESTHESIA OF TRACHEAL RECEPTORS

Two types of sensory receptors were individually identified in dogs on the exposed mucosa of the extrathoracic trachea: slowly adapting stretch receptors (SAR) and rapidly adapting receptors (RAR). Increasing concentrations of lidocaine (L), bupivacaine (B), and tetracaine (T) solutions were topically applied on the mucosa over the sensory fields of the receptors, while their neural activity in response to an appropriate stimulus was recorded. Action potentials from SARs were blocked by the anesthetic at a much higher concentration and with larger exposure times than potentials evoked from RARs (mean values: L = 51.1 mM for 7.4 min and 1.48 mM for 1.03 min, respectively; B = 9.4 min and 0.13 mM for 0.23 min; and T = 4.9 mM for 9.8 min and 0.06 mM for 2 min). The minimal blocking concentration of the topical anesthetics varied widely (L=20 times, B=5, and T=5) among SARs and less (L = 3.2, B = 2, and T = 4) among RARs. These results could be explained by a different location in the mucosa of the two types of receptors and suggest the feasibility of a differential blockade by topical anesthetics.