Opposite responses to lidocaine between intrapulmonary mechanical and chemical sensors

We attempted to determine whether intrapulmonary sensory receptors are nourished by the pulmonary or the systemic circulation. Single-unit activity from the cervical vagus nerve was recorded in anesthetized, open chest, mechanically ventilated rabbits, comparing responses to right or left ventricular injection of 2% lidocaine (at 4 mg/kg). Airway mechanosensors [slowly adapting receptor (SARs) and rapidly adapting receptors] were inhibited by lidocaine, whereas chemosensors (C-fiber receptors and high-threshold A delta-receptors) were stimulated. Furthermore, all types of airway sensors were perfused preferentially by the pulmonary circulation. For example, 14 of the 15 tested SARs ceased discharge at 4.1 +/- 0.6 s after lidocaine injection into the right ventricle. The blocking effect lasted 35 +/- 6.2 s. In contrast, none of the 15 SARs ceased their activity after lidocaine injection into the left ventricle. Our data show that intrapulmonary sensors are mainly nourished by the pulmonary circulation. Their very short latency indicates that these sensors receive ample blood supply. Thus, intrapulmonary sensors rely on the pulmonary circulation to detect bioactive agents in the blood.