No effect of pure oxygen inhalation on headache induced by glyceryl trinitrate

Inhalation of hyperbaric oxygen has been used as an experimental treatment for migraine and pure oxygen is an established treatment for cluster headache. Intravenous glyceryl trinitrate (GTN) is an established headache model. In the present study the possibility of decreasing the headache by inhalation of pure oxygen was explored in a double-blind crossover design in 18 healthy subjects. Inhalation of air served as placebo. The subjects received intravenous GTN (0.25 µg/kg/min) for 20 min. Headache was scored for 85 min. Sixteen of 18 (89%) subjects experienced GTN-induced headache after O₂-inhalation and 17/18 (94%) experienced GTN-induced headache after air. The mean peak headache scores were 1.9 and 2.4, respectively, on a numerical scale of 0–10. Oxygen inhalation did not have effect on GTN-induced headache, most likely because the theoretical decrease in NO levels, due to faster metabolism of NO, is too small to be detected in the GTN headache model.