A Comparison of Cardiac Outputs,Determined by Direct Fick and Pressure Pulse Methods

A method of determining cardiac output that is more rapid than the standard procedures, and with less dependence on skilled technical help has long been needed. With the publication by Hamilton and Remington 1 of a method for determining stroke volume from a pressure pulse this need has been met if their results are reproducible by others. In addition, their method has the added advantage, for the pharmacologist, of being able to follow the actions of a drug on the output from stroke to stroke.

Using the dye method as their basis of comparison, they found a correlation of r = +0.994 with an average variation between the two measurements of ±8.2% with a range of +35 to −13%. While the dye method has been shown to give compara-able to the Fick method 2 within ± 10%, it seemed essential that a comparison be made between the Fick and the pressure pulse method not only to compare the accuracy of the pressure pulse method but to check our own calculations of cardiac output by that method.

Methods. A total of 8 dogs were used and 15 outputs were determined under a variety of conditions. The dogs were anesthetized with sodium barbital 300 mg/kg administered orally or intraperitoneally. Pressure pulses were obtained by means of a Hamilton manometer 3 of adequate frequency. A No. 9 ureteral catheter was passed down the right jugular to the right ventricle and the position verified by fluoroscopy. A slow, heparinized saline drip was maintained through the catheter. Oxygen consumption was measured by connecting the dog to a McKesson Recording Metabolor, with a tracheal cannula. Blood samples were taken under oil simultaneously from the right ventricle and a femoral artery and promptly iced.