Objective: To evaluate in humans the mechanisms underlying the increase in nasal mucosal temperature following immersion of the feet in warm water (42 degrees C).
Material and methods: The nasal mucosal temperature of subjects was measured whilst their feet were immersed in warm water.
Results: The nasal mucosal temperature rose quickly on immersion and dissipated equally fast on removal of the feet from warm water. Intranasal lidocaine raised the mucosal temperature slightly after application, but also blocked the feet warming-induced increase in nasal mucosal temperature, suggesting a neural reflex. Whereas the cutaneous-nasal reflex stimulates a transient parasympathetic response, acetylcholine does not seem to contribute to the more prolonged increase in nasal mucosal temperature following immersion of the feet in warm water. Warming of the feet probably leads to a loss of alpha-sympathetic activity of nasal blood vessels and an increase in nasal mucosal temperature because application of phenoxybenzamine, an alpha-sympathetic blocking agent, to the nasal mucosa increased the nasal mucosal temperature.
Conclusions: Our data suggest that the increase in nasal mucosal temperature after warming of the feet is mediated by a neural reflex, which is caused by loss of sympathetic activity of the nasal vasculature and a possible additional contribution of a long-acting parasympathetic mediator.