A crucial question in placebo research is related to which conditions and physiological functions are affected by placebos. Here we present evidence that critical life functions, like ventilation, oxygenation, circulation, and perfusion, can be sensitive to placebo treatments in some circumstances. Indeed, we have investigated the role of placebo effects at an altitude of 3500m, where oxygen pressure is 64% compared to the sea level. In these extreme conditions, hypoxia triggers several compensatory responses, such as hyperventilation, increased cardiac output, and increased brain perfusion. A conditioned placebo procedure was found to mimic the effects of oxygen on these compensatory responses, and these effects are still present at altitudes as high as 4500 and 5500m, where oxygen pressure is only 57% and 50%, respectively, compared to the sea level. Thus, placebo effects also take place for those functions that are critical for life and whereby oxygen is the key element.
Keywords: Critical life functions; High altitude; Hypoxia; Nocebo; Oxygen; Placebo.
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