French researchers have discovered potential risk factors for severe high altitude illness (SHAI).
The researchers also found that taking acetazolamide (ACZ), a drug frequently prescribed to prevent altitude illness, can reduce some of the risk factors associated with SHAI.
The three exercise-related factors identified by the researchers include oxygen desaturation at exercise (Sae), hypoxic cardiac response at exercise (HCRe) and hypoxic ventilatory response at exercise (HVRe).
Sae measures the amount of oxygen that is in the blood during exercise; HCRe measures the heart's response to exercise in a hypoxic, or low oxygen, setting, and HVRe refers to respiratory changes (notably rapid breathing) that occur during exercise in a hypoxic setting.
The researchers measured these parameters in controlled, hypoxic conditions in a lab setting that mimicked high-altitude conditions.
"These results suggest that HCRe, HVRe and substantial decreases in Sae are independent risk factors of SHAI, and that decreases in Sae and HVRe can be used to accurately predict the risk of developing SHAI," said Jean-Paul Richalet, MD, PhD, a professor of physiology at Universit? Paris 13.
"To date, this is the largest epidemiological study of subjects exposed to high altitude-related illness, who were previously evaluated for their responses to hypoxia," he added.
The researchers collected data from 1,326 men and women who were seen prior to high-altitude excursions, which included at least 3 days above 4,000 meters with overnight sleeping above 3,500 meters.
Next, study participants went through a routine hypoxic exercise test, which consisted of four, four-minute phases: rest at normal oxygen levels; rest at hypoxic levels; exercise in hypoxia; and exercise in normal levels of oxygen. During the exercise test, the researchers measured heart rate, breathing and blood oxygen levels.
Following their excursions, study participants were asked to complete a questionnaire to determine if they had experienced any symptoms of high altitude illness.
Among the 1,326 questionnaire respondents, 318 reported that they had experienced a severe altitude illness during their high-altitude excursion, including 105 who used ACZ and 213 who did not.
Researchers also found that preventive use of ACZ resulted in a 44 percent reduction in the risk of developing SHAI.
The study has been published in the American Journal of Respiratory and Critical Care Medicine.