LACRIMATION AND CUTANEOUS VASODILATATION IN THE FACE INDUCED BY PAINFUL STIMULATION OF THE NASAL ALA AND UPPER LIP

The effect of painful stimulation of the nasal ala and upper lip on lacrimation and cutaneous vascular responses in the forehead and cheeks was investigated in 11 normal subjects. In addition, the mechanism of the response was studied in 10 patients with a lesion compromising parasympathetic activity in the facial nerve. In normal subjects, pinching the nasal ala with forceps increased blood flow on the ipsilateral side of the forehead but not the cheek. Pinching the upper-lip induced ipsilateral vasodilation in the forehead in 3 of 11 subjects, but not in the cheek. Pinching either site increased corneal moisture proportional to the size of the vascular response in the forehead. A facial nerve lesion inhibited the ipsilateral component of the vascular response in the forehead. These findings suggest that pain within the distribution of the first or second divisions of the trigeminal nerve excites vasodilator and lacrimal reflexes in the facial nerve. The increase in cutaneous flow during this trigeminal-parasympathetic reflex appears to be limited to the forehead.