Oxygen inhalation has no effect on provoked cranial autonomic symptoms using kinetic oscillation stimulation in healthy volunteers

Objective
Inhalation of oxygen is highly effective in cluster headache, a subtype of trigeminal autonomic cephalgias. Since oxygen has no effect on nociceptive pain, the mechanism of action is still unknown. The present study investigated whether oxygen inhalation modifies the trigeminal autonomic reflex arc in healthy volunteers.
Methods
21 healthy volunteers participated in a randomized, placebo controlled, double-blind, cross-over, and within-subject study design. In a randomized order demand valve inhalation of 100% oxygen or medical air were administered. Capillary blood samples were collected to control for blood gas changes. Cranial parasympathetic output (lacrimation) was provoked using kinetic oscillation stimulation of the nasal mucosa. Standardized measurement of lacrimation between baseline and kinetic oscillation stimulation served as a measure of induced cranial autonomic output.
Results
There was no significant difference in parasympathetic output after oxygen inhalation when compared to inhalation of medical air.
Conclusion
The inhalation of 100% oxygen does not affect the parasympathetic reflex arc of the trigeminal autonomic reflex.