Estimation of Cardiac Output from the Rate of Change of Alveolar Carbon Dioxide Pressure during Rebreathing

Abstract
A new CO2-rebreathing method for estimating cardiac output is described, and compared with a method employing N2O performed at the same time. The subject inhales from a reservoir of 30% O2 in N2 and rebreathes into and out of an empty bag for 10 s. Oxygenated mixed venous CO2 pressure is then determined by rebreathing 7-15% CO2 in O2, the mixture being selected to obtain a plateau of CO2 concentration. The method can be employed for estimating pulmonary blood flow during physiological studies in subjects with normal lungs.