Beeinflussung des Strömungswiderstands der Atemwege durch CO2-Inhalation

Based on previous studies, a change in the parameters of the arterial vascular system (resistance, compliance) due to transcutaneously incorporated carbon dioxide could be determined. In order to assess a possible change in the parameters of the histologically similar airway system by inhalation of CO2-air mixture, 18 test persons were examined. In addition to the parameters of the capnogram (slope of the rising, plateau, falling phase and end-expiratory CO2 concentration) and the forced flow-volume curve (1-second capacity, maximum expiratory flow, forced vital capacity and maximal expiratory flow at 25% / 50% / 75% of the forced vital capacity), as well as the arterial CO2 partial pressure were recorded invasively. Under the influence of the CO2-air mixture inhalation, the slope increased in the rising phase, while those in the plateau and falling phases of the capnogram decreased. In the case of the parameters of the forced flow-volume curve, a significant increase could be registered only with the maximum expiratory flow at 75% of the forced vital capacity. A mathematical model of the bronchial tree was developed in parallel to the experimental investigation for the purpose of assigning changes due to CO2-air mixture inhalation to physiological parameters of the airway system (airway cross-section, resistance). By solving the inverse problem by fitting the flow-volume curve of the model to the real flow-volume curve, the airway resistances of the generations 0 to 23 could be determined. It has been shown that the airway resistance of generations 8 to 15 (zone 2) decreases as a result of the CO2-air mixture inhalation. The model oriented approach has proved to be favorable for the evaluation of CO2-air mixture inhalation, although an extension of the model approach by improvements in the calculation of the retraction pressure as well as the consideration of the asymmetry of the bronchial tree appears necessary. With such an extended model, a more precise identification strategy for quantifying effects of the CO2-air mixture inhalation is conceivable.