A continuous cardiac output computer based on thermodilution principles.

A totally self-contained instrument for the measurement of cardiac output is described. The microcomputer controlled instrument is based upon the principles of thermodilution and is capable of making cardiac output determinations on a minute by minute basis. A bolus of heat is delivered to the blood via a resistive heating element wound on the surface of a conventional thermodilution catheter, and the resulting transient pulmonary artery blood temperature increases is monitored with the thermistor located near the tip of the catheter. The performance of the instrument was tested in a mock circulatory loop and in dogs for periods of up to 13 hours. The accuracy and reproducibility of flow determinations made with the system compare favorably with those made with a conventional cardiac output monitor. This study demonstrates the feasibility of a stand-alone cardiac output computer that can provide virtually continuous measurements of blood flow without the intervention of a technician.