Because of anecdotal reports of CO2-related symptoms onboard the International Space Station (ISS), the relationship between CO2 and in-flight headaches was analyzed.
Headache reports and CO2 measurements were obtained, and arithmetic means and single-point maxima were determined for 24-hour and 7-day periods. Multiple imputation addressed missing data, and logistic regression modeled the relationship between CO2, headache probability, and covariates.
CO2 level, age at launch, time in-flight, and data source were significantly associated with headache. For each 1-mm Hg increase in CO2, the odds of a crew member reporting a headache doubled. To keep the risk of headache below 1%, average 7-day CO2 would need to be maintained below 2.5 mm Hg (current ISS range: 1 to 9 mm Hg).
Although headache incidence was not high, results suggest an increased susceptibility to physiological effects of CO2 in-flight.
From the NASA Johnson Space Center (Dr Law, Ms Van Baalen, Dr Meyers, and Dr Alexander), Wyle Science, Technology and Engineering (Drs Foy and Wear), and MEI Technologies (Mrs Mason and Ms Mendez), Houston, Tex.
Address correspondence to: Jennifer Law, MD, MPH, 2101 NASA Parkway, Mail Code SD2, Houston, TX 77058 (firstname.lastname@example.org).
The authors declare no conflicts of interest.