How do changes in exhaled CO2 measure changes in cardiac output? A numerical analysis model

• Published in: Journal of clinical monitoring and computing 2010-12, Vol.24 (6), p.413-419
• Main Author: Breen, Peter H.
• Format: Article
• Language: English
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Anesthesiology; Animals; Biological and medical sciences; Blood Pressure - physiology; Carbon Dioxide - metabolism; Cardiac Output - physiology; Computer Simulation; Critical Care Medicine; Dogs; Emergency and intensive cardiocirculatory care. Cardiogenic shock. Coronary intensive care; Exhalation - physiology; Health Sciences; Intensive; Intensive care medicine; Medical sciences; Medicine; Medicine & Public Health; Models, Biological; Pulmonary Gas Exchange - physiology; Statistics for Life Sciences
• ISSN: 1387-1307; 1573-2614
• DOI: 10.1007/s10877-010-9263-z

Objective In a previous study in anesthetized animals, the slope of percent decreases in exhaled CO 2 versus percent decreases in cardiac output ( inflation of vena cava balloons) was 0.73. To examine the mechanisms underlying this exhaled CO 2 - relationship, an iterative numerical analysis computer model of non-steady state CO 2 kinetics was developed. Methods The model consisted of a large peripheral tissue compartment connected by venous return and to a small central pulmonary compartment. Equations were developed to describe the movement of CO 2 in this system. Decreases in were accompanied by experimentally measured increases in alveolar dead space fraction (V d alv /V t alv ), generated by decreased pulmonary vascular pressure during the decrease. Results When the model was perturbed by a 40% decrease in and an increase in V d alv /V t alv from 5 to 20.6%, average alveolar expired ( ) decreased from 37.5 to 29.4 mm Hg, similar to the animal experiments. Due to the high peripheral tissue compliance for CO 2 , the computer model demonstrated that, after a decrease in , at least 1 h was required for compartment CO 2 stores to approach a new equilibrium state. Conclusions The numerical analysis computer model helps to delineate the mechanisms underlying how decreased resulted in decreased exhaled CO 2 . The model permitted deconvolution of the effects of simultaneous variables and the interrogation of parameters that would be difficult to measure in actual experiments.