Airway and pulmonary tissue responses to capsaicin in guinea pigs assessed with the alveolar capsule technique.

We studied the effects of capsaicin on airway and lung tissue mechanics in anesthetized and tracheostomized guinea pigs that were mechanically ventilated at constant tidal volume (8 ml/kg) and breathing frequency (60 breaths/min). Dose-response curves to intravenously infused capsaicin (1, 10, and 100 micrograms/kg) were performed (five animals for each dose, one dose per animal). We measured airflow, volume (by integration of the flow signal), tracheal pressure, and alveolar pressure with an alveolar capsule. Capsaicin induced a dose-dependent increase in airway resistance, tissue resistance, and dynamic elastance. The relationship between airway pressure and flow was fitted by a quadratic (Rohrer) equation. Airflow became more turbulent after infusion of capsaicin. After infusion of 100 micrograms/kg capsaicin, airway pressure (at flow rates of 10 ml.s-1) increased from 3.03 +/- 0.40 (mean +/- SEM) to 9.58 +/- 1.88 cm H2O, whereas the pressure corresponding to viscoelastic properties of lung tissue increased from 0.92 +/- 0.14 to 8.58 +/- 1.12 cm H2O. We conclude that infusion of capsaicin results in mechanical effects in both airways and pulmonary tissue.