DeGroot DW, Devine JA, Fulco CS. Incidence of adverse reactions from 23,000 exposures to simulated terrestrial altitudes up to 8900 m.Aviat Space Environ Med; 74:994–7. Introduction:Adverse reactions during hypobaric chamber operations result from changes in barometric pressure per se and to the related reductions in the partial pressure of inspired oxygen. Previous studies have indicated that an adverse reaction may occur in ∼6% of exposures in chambers used for flight training. The purpose of this study was to determine the rate of adverse reactions in a chamber used exclusively for terrestrial altitude research studies. Methods: Data for incidence of ear block, sinus block, toothache, and other adverse reactions were analyzed using a master history file that contained information such as annual and total number of studies and human exposures, and onset and outcome of adverse reactions. Incidence for a given time period was calculated as (# of reactions × 100)/(# of exposures). Results: In 33 yr, there have been 23,656 human exposures and 296 adverse reactions. The overall incidence was 1.25 reactions per 100 exposures (0.72 for research volunteers and 0.53 for staff). The majority (75% of all reactions) were ear blocks (0.93 reactions per 100 exposures). Staff members were more likely than research volunteers to have more than one reaction. Discussion: The incidence of 1.25 reactions per 100 exposures for our chamber is considerably lower than that reported in the literature. This is due primarily to our use of lower altitudes and slower rates of ascent and descent compared with other facilities whose emphasis is on aircraft flight training.
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