Neurogenic inflammation in the airways: characterisation of electrical parameters for vagus nerve stimulation in the guinea pig.

We systematically determined the electrical parameters optimal for inducing plasma leakage in the airways of the anaesthetised, unventilated guinea pig but with minimal effects on carotid artery pressure in response to bilateral vagus nerve stimulation. The magnitude of both plasma leakage and of the reductions in blood pressure was dependent upon the frequency, amplitude and pulse width of the stimulus and on the duration for which it was applied. At 7 Hz, 5 V, 5 ms for 3 min leakage was increased above controls by 161% in the lower trachea, by 200% in the main bronchi and by 77% in the proximal intrapulmonary airways, with only a 21% drop in blood pressure. Neither increasing the intensity and duration of the stimulus nor allowing leakage to increase in magnitude with time after a short stimulus caused significant further increases in leakage but did cause concomitant reductions in blood pressure. Vagally-induced leakage and reduced blood pressure were abolished by pretreatment of the animals with capsaicin. Thus, the involvement of non-adrenergic, non-cholinergic mechanisms in the response to these stimulation parameters indicates that they are suitable for the study of neurogenic inflammation in the airways and its modulation by drugs, some of which may affect blood pressure.