Changes in the carbon dioxide expirogram in response to ozone exposure

The objectives of this study were to quantify pulmonary responses to ozone (O3) exposure by parameters computed from the carbon dioxide expirogram and to compare these responses to decrements in forced expired spirometry. Anatomical dead space (VD) was determined from the pure dead space and transition regions of the expirogram. Four alternative parameters were computed from the alveolar plateau: slope (S), normalized slope (NS), peripheral cross-sectional area (AP) and well-mixed peripheral volume (VMP). Forty-seven healthy nonsmokers (25 men and 22 women) participated in two research sessions in which they exercised on a cycle ergometer for 1 h while orally inhaling either room air at a minute ventilation of 30.6 ± 3.6 L or room air mixed with 0.252 ± 0.029 ppm O3 at a minute ventilation of 29.9 ± 3.7 L. Carbon dioxide expirograms were measured before exposure, 10 min after exposure and 70 min after exposure. Percent changes (mean ± SD) in expirogram parameters were significant (P ≤ 0.002) at both 10 and 70 min after O3 exposure: VD(−4.2 ± 5.1, −3.3 ± 6.9), S(16.4 ± 17.9, +15.1 ± 20.2), NS(17.5 ± 15.4, +15.9 ± 19.2), AP(−8.1 ± 7.6, −7.7 ± 9.8) and VMP(−15.4 ± 13.0, −13.0 ± 15.2). Percent decrements of forced expired volume in one second (FEV1) were also significant at both 10 min (−13.3 ± 13.4) and 70 min (−11.1 ± 9.2) following O3 exposure. Changes in the expirogram as well as decrements in FEV1 were not significant at either time point after air exposure. Thus, the CO2 expirogram is useful for characterizing the effect of O3 exposure on gas transport, and for supplementing forced expired spirometry that is frequently used to quantify lung mechanics.