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High-Altitude Syncope: History Repeats Itself-Reply

Richard A. Nicholas, MD; Patrick D. O'Meara, DO
JAMA. 1993;269(5):587. doi:10.1001/jama.1993.03500050065016.
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In Reply.  —We are indebted to Dr Perrill for bringing to our attention the article by Henderson et al1 mentioning syncope at high altitude. The article, a fascinating series of studies regarding "the protection of aviators against the effects of high altitudes, low barometric pressure, and deficiency of oxygen," reports that several subjects had syncope or near syncope during hypobaric chamber studies simulating altitudes up to 10 500 m.An impressive 66% of subjects in their study had a fall in diastolic blood pressure. "In at least half of these the fall was sudden and great. It is always associated with fainting...." The fall in pressure was noted at oxygen levels as low as 14%, simulating an altitude of 3120 m. This was hypothesized to be secondary to "overcoming the vasomotor center by oxygen shortage." The authors note that subjects had varying responses to hypoxic stress and deduce that


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