Research supports the connection between breathing manipulation and emotional states, yet there is no established standard of quantification. This preliminary study investigates the validity and efficacy of a simple, practical test of tolerance to endogenous carbon dioxide tolerance as an index of anxiety. A sample of 41 nonclinical participants (24 males, 17 females) performed three trials of a CO2 tolerance test (CO2 TT)— a maximal duration exhale from vital capacity—on two separate days.
The CO2 TT out-performed a breath-hold test as an index of state anxiety. The findings of this study suggest that CO2 tolerance (CO2 T), as measured by a maximal duration exhale from vital capacity, serves as an index for state, and to a lesser degree, trait anxiety. With additional future research, CO2 T could become an important and easily accessible tool in assessing levels of and changes in anxiety.