Student Research: Chiung-I Hwang

The End-Tidal Carbon Dioxide Concentrations in Adult Women
Faculty Advisor: 


Carbon dioxide in expired air has been proposed as a normalizing factor in breath analysis to adjust for the varibale effects of breathing pattern or mixed-expired gas concentrations of solvents. It is based on the assumption that carbon dioxide, as well as solvent vapors, will reach equilibrium in alveolar air and pulmonary blood, and the concentrations of carbon dioxide and solvent vapors are affected similarly by breathing patterns.

Most of the studies of carbon dioxde have been limited to male subjects. The reproductive endocrinology of women, and cyclic changes of pituitary and ovarian hormones suggest CO2 levels may be different from men. This experiment was designed to investigate the variance of end-tidal carbon dioxide in women and the possibility of menstrual cycle effects on endtidal carbon dioxide concentration. Twelve females volunteered to participate in the experiment. The experiment involved the measurement of end-tidal carbon dioxide concentration once a week for 5 o 11 weeks. The procedure included normal breathing, 15 seconds of breath holding, and 15 seconds of hyperventilation. Physical conditions, time in the menstrual cycle, and other varibales were recorded at each session.

Neither the menstrual cycles of subjects nor other variables were found to significantly correlate with end-tidal carbon dioxide lvels. The end-tidal carbon dioxide concentrations of 12 female subjects ranged from 4.38 to 5.37% with the group average of 4.86%. The result is close to the previous study with a mean oof 4.8% in male subjects. Coefficients of variation of each female subject ranged from 2.37 to 11.14%, which is larger than 2.00 to 9.32% in male subjects.

The within-subject variation was small. It suggests that individual subjects replicated end-tidal CO2 data well through a period of time. Therefore, the use of individual end-tidal CO2 values as a standardizing factor for breath sampling should be reliable.