Continuous thermodilution cardiac output measurement in sheep.

A technique has been developed to continuously measure cardiac output by means of the principles of thermodilution. Pulmonary artery catheters were modified by placing a 10 cm filament near the usual injectate port. Small amounts of heat were infused according to a randomly repeating binary on-off sequence. The distal blood temperature was recorded and cross-correlated with the heat waveform to produce a dilution curve and calculate cardiac output. The technique was compared with bolus thermodilution in seven sheep. Cardiac output ranged from 1.5 to 13.2 L/min, and heart rate varied from 59 to 180 beats/min. The linear regression between the data obtained by the two methods is represented by the equation y = 1.00x + 0.13; the correlation coefficient, R, is 0.97, and the p value is less than 0.0001.