Modeling cardio-respiratory system response to inhaled CO2 in patients with congestive heart failure

In this paper we examine a cardiovascular-respiratory model of mid-level complexity designed to predict the dynamics of end-tidal carbon dioxide (CO₂) and cerebral blood flow velocity in response to a CO₂ challenge. Respiratory problems often emerge as heart function diminishes in congestive heart failure patients. To assess system function, various tests can be performed including inhalation of a higher than normal CO₂ level. CO₂ is a key quantity firstly because any perturbation in system CO₂ quickly influences ventilation (oxygen perturbations need to be more severe). Secondly, the CO₂ response gain has been associated with respiratory system control instability. Thirdly, CO₂ in a short time impacts the degree of cerebral vascular constriction, allowing for the assessment of cerebral vasculature function. The presented model can be used to study key system characteristics including cerebral vessel CO₂ reactivity and ventilatory feedback factors influencing ventilatory stability in patients with congestive heart failure. Accurate modeling of the dynamics of system response to CO₂ challenge, in conjunction with robust parameter identification of key system parameters, can help in assessing patient system status.