Parasympathetic activity assessed by diving reflex and by airway response to methacholine in bronchial asthma and rhinitis.

It has been suggested that airway hyperreactivity in asthma is associated with increased parasympathetic tone. We have accordingly assessed parasympathetic responsiveness in five groups of subjects (17 normal controls, 8 patients with extrinsic rhinitis, 6 with intrinsic rhinitis, 10 extrinsic asthmatic patients, 7 intrinsic asthmatic patients) by examining their responses to both diving reflex and methacholine inhalation challenge. The mean fall in heart rate during the diving test was significantly greater in asthmatic subjects than in normal controls and in patients with rhinitis. The diving-induced bradycardia was significantly greater in intrinsic than in extrinsic asthmatic subjects. There was a good correlation between the drop in heart rate during diving test and the provocation dose of methacholine producing a 45% decrease in specific airway conductance both in patients with rhinitis and in asthmatic patients. There was a less good correlation between diving response and clinical severity score in the same asthmatic patients. These results indicate that intrinsic asthma is associated with a marked degree of cholinergic hyperreactivity. The diving test seems to provide an accurate method for the analysis of the parasympathetic system in asthma.