Transient respiratory response to hypercapnia: Analysis via a cardiopulmonary simulation model

In recent years, our group has developed a comprehensive cardiopulmonary (CP) model that comprises the heart, systemic and pulmonary circulations, lung mechanics and gas exchange, tissue metabolism, and cardiovascular and respiratory control mechanisms. In this paper, we analyze the response of the model to hypercapnic conditions and hence focus on the chemoreflex control mechanism. Particularly, we have enhanced the peripheral chemoreceptor model in order to better reflect respiratory control physiology. Using the CO₂ fraction in the inspired air as input to the CP model, we were able to analyze the transient response of the system to CO₂ step input at different levels, in terms of alveolar gas partial pressures, tidal volume, minute ventilation and respiratory frequency. Model predictions were tested against experimental data from human subjects [1]. Results show good agreement for all the variables under study during the transient phases and low root mean square errors at steady state. This indicates the potential for the model to be used as a valid tool for clinical practice and medical research, providing a complementary way to experience-based clinical decisions.