The effects of parasympathetic activity on bronchial tone

Current opinion is that a vagal stimulation is beneficial for the cardiovascular apparatus but also causes airflow obstruction. The aim of this study was to examine this paradox. By using the within-breath Forced Oscillation Technique, inspiratory resistance and reactance at 5 Hz (R5 and X5, respectively) and cardio-vascular activity can be simultaneously measured humans at baseline and during baroreceptors stimulation by neck suction, allowing the study of the correlation between the parasympathetic activation and airway caliber. Correlation between changes in lung function and neck suction at 0.1Hz was tested in 15 volunteers using the cross-spectrum between either R5 or X5 and the stimulating waveform. Baroreceptors stimulation induced cardiovascular changes compatible with parasympathetic activation. The magnitude of the cross-spectrum between the pressure swings applied to the neck and both R5 and X5 presented a peak at 0.1 Hz with a higher coherence for R5 than X5. On average, R5 slightly but significantly increased compared to baseline, while changes in X5 were negligible. The response to the stimulation was highly variable among subjects.