Pain, 2015 Nov; 156(11):2326-36
HIGH-ALTITUDE HEADACHE: THE EFFECTS OF REAL VS SHAM OXYGEN ADMINISTRATION
Fabrizio Benedetti a,b,*, Jennifer Durando b, Lucia Giudetti c, Alan Pampallona c, Sergio Vighettia,b
a Department of Neuroscience, University of Turin Medical School, Turin, Italy,
b INN-CNR Plateau Rosa Laboratories, Breuil-Cervinia/Zermatt, Italy/Switzerland,
c Giancarlo Quarta Foundation, Milan, Italy
High-altitude, or hypobaric hypoxia, headache has recently emerged as an interesting model to study placebo and nocebo responses, and particularly their peripheral mechanisms. In this study, we analyze the response of this type of headache to either real or sham (placebo) oxygen (O2) administration at an altitude of 3500 m, where blood oxygen saturation (SO2) drops from the normal value of about 98% to about 85%. In a trial in which a double-blind administration of either 100% O2 or sham O2 was administered, we tested pre- and post-exercise headache, along with fatigue, heart rate (HR) responses, and prostaglandin E2 (PGE2) salivary concentration. Although real O2 breathing increased SO2 along with a decrease in pre- and post-exercise headache, fatigue, HR, and PGE2, placebo O2 changed neither pre-/post-exercise headache nor SO2/HR/PGE2, but it decreased fatigue. However, in another group of subjects, when sham O2 was delivered after 2 previous exposures to O2 (O2 preconditioning), it decreased fatigue, post-exercise headache, HR, and PGE2, yet without any increase in SO2. Three main findings emerge from these data. First, placebo O2 is effective in reducing post-exercise headache, along with HR and PGE2 decrease, only after O2 preconditioning. Second, pre-exercise (at rest) headache is not affected by placebo O2, which emphasizes the limits of a placebo treatment at high altitude. Third, fatigue is affected by placebo O2 even without prior O2 conditioning, which suggests the higher placebo sensitivity of fatigue compared with headache pain at high altitude.
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