Noninvasive measurement of cardiac output during exercise - physiologic model, simulation and clinical implementation

The acetylene-helium rebreathing technique (ART) is a noninvasive method for estimating cardiac output (Q). This method is used clinically to assess hemodynamic responses to exercise. The standard ART requires deep, fast breathing and emptying of the rebreathing bag on each breath to assure good gas mixing and appropriate data for analysis. Although a nonforced breathing pattern is preferrable for children, it requires a more sophisticated method of analysis. For this purpose the authors used a mathematical model to describe the concentration dynamics of the tracer gases over successive breaths. Cardiac output is a parameter of the model which can be estimated from the data by a nonlinear least-squares method. A feasibility study of this approach is presented.