An Assessment of a N2O Rebreathing Method for the Estimation of Cardiac Output During Severe Exercise

Cardiac output was measured as pulmonary blood flow by a non-invasive N2O rebreathing technique during exercise at submaximal and maximal work levels in three subjects. The standard deviation of repeated measurements over a period of 6-20 weeks was ±1·51 min −1 at all levels of work and in all subjects. This level of variability is comparable to that found in using the dye dilution and direct (O2) Fick methods in individual subjects during a more limited time span, and suggests that the method can be used effectively in non-steady state and maximal conditions of dynamic exercise.