[Expiratory capnography in asthma. Perspectives in the use and monitoring in children].

The shape of the capnogram, which is related to uneven ventilation, is modified in obstructive diseases and especially during crisis of asthma. The most significant change is a rise in the slope of the "alveolar plateau". In this study, we measured the end-tidal slope (ETS) of the capnogram, calculated on 0.36 s before the end of expiration, and we compared this indice to usual spirometric measurements (FEV 1) in 21 control subjects and in 24 asthmatic subjects. The mean ETS in control subject was 0.08 +/- 0.06%/s, it was 0.3 +/- 0.23% in asthmatic subjects (p < 0.001). In the latter, we found a very significant correlation between ETS and FEV 1 (r = 0.83, p < 0.001). Thirteen asthmatic subjects were tested for a second time, immediately after inhalation of a beta 2-mimetic drug. They exhibit a very strong correlation between the rise of FEV 1 and the loss of ETS (r = 0.96, p < 0.001). These results show that the analysis of the capnogram's shape is a quantitative method for evaluating the severity of the bronchospasm. This ability, added to specific advantages (non-invasiveness, effort-independence) opens new fields of application to capnography: measurement of the bronchospasm in children, computerized monitoring of asthma.