Use of a simulation model for estimating cardiac output from aortic pressure curves

A method for calculating cardiac output from aortic pressure curves is presented. The method is based on a simulation model of the human cardiovascular system. The aortic compliance is calculated from the pulse transmission time in the aorta. The method has been tested against standard cardiac output measurements in 61 instances in 39 persons. 40 measurements have been performed at rest, while 21 have been performed during various changes in the cardiovascular state. The mean difference between the pulse method and the standard cardiac output determination was found to be 9% with a standard error of the difference of 7%. The correlation coefficient was r=0·96. The largest differences were found in patients suffering from atrial fibrillation, where changes in pressure in the aorta made compliance estimates based on pulse transmission time difficult. Using a servosystem, the model is capable of following changes in the cardiovascular state within a few beats. This method should therefore be useful for calculating cardiac output in the intensive-care situation.