A simple analogue computer for cardiac output determination by thermodilution.

Abstract

A cardiac output (CO) computer with digital presentation of calculated CO values has been constructed. The computer system and calibration technique is described. The computer utilizes the thermodilution principle and a dual-thermistor technique, which allows direct recording of the temperature difference between the injected cold saline bolus and the blood as well as the temperature variations in the pulmonary artery caused by the dilution of the injected saline bolus. Due to the insignificant recirculation phenomenon, the total area of the pulmonary artery blood temperature dilution curve is used in the Stewart-Hamilton formula, allowing an easy integration technique. A memory block in the computer certifies that the baseline of the dilution area is representative. An electrical 'acceptance window' is used for the decision whether a dilution curve is acceptable or not. The instrument has been applied in a clinical material. The CO calculated by the computer has the same validity as that of the dye dilution method and a reproducibility in the same range as other methods for CO estimations. Errors in the management of the computer are discussed.