Automation of a noninvasive cardiac output computation from respiratory gases and flow

We describe work completed and discuss future work on the automation of a real-time, non-invasive method for calculating Cardiac Output. This method [1] uses concentrations of oxygen and carbon dioxide in the inspiration and exhalation segments of a breath cycle, atmospheric pressure, and total respiratory degrees ow to estimate the relationship between partial pressure of alveolar CO2 and the instantaneous gas exchange ratio (R). Known physiological relationships between R and the partial pressures of CO2 on both the venous and arterial sides of the lung, in conjunction with the Indirect Fick Equation, allows us to determine a patient's breath-by-breath Cardiac Output. This method is now feasible in real-time with the development of a prototype non-invasive metabolic monitor that utilizes a micro- degrees uidic gas analyzerlable to simultaneously measure the constituent concentrations of three-gas mixtures in real-time at a fractional cost of other hardware and methods.