Neural control of airway to deep inhalation in rabbits

Bronchodilation induced by a deep inhalation (DI) is usually attributed to the mechanical interdependence between airways and parenchyma. The aim of the study was to evaluate the contribution of neural control of the airway in the response to DI. In mechanically ventilated rabbits, cervical vagi were cooled using 2 Peltier elements. Lung resistance was measured before and up to 2 min after a DI at vagus nerve temperature = 37 °C (R(L37 °C)), 8 °C (R(L8 °C)) and 4 °C (R(L4 °C)). Measurements were performed in control conditions (Ctrl) and during infusion of methacholine (Mch). At Ctrl, R(L8 °C) and R(L4 °C) were significantly lower than R(L37 °C). After Mch, however, R(L4 °C) was not different from R(L37 °C), both being significantly higher than R(L8 °C). Vagal cold block (VCB) abolished the bronchodilation observed after the control DI and reduced its magnitude after Mch. The magnitude of bronchodilation immediately after the DI was significantly related to baseline R(L) at any vagal temperature (p < 0.001), but the renarrowing was more strongly related to baseline R(L) after VCB than at baseline. The data indicate a significant contribution of respiratory reflexes to the airway response after DI, highlight the influence of vagal control of airway wall visco-elasticity and suggests the occurrence of a moderate reflex bronchodilation in response to Mch.