Continuous cardiac output by thermodilution.
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Biomedical subjects
Publications and source records attributed to M Yelderman.
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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.
The limitations of developing a technique to measure cardiac output continuously are given. Logical explanations are provided for the economic, technical, and physiologic benefits of a stochastic system identification technique for measuring cardiac output. Heat is supplied by a catheter-mounted filament driven according to a pseudorandom binary sequence. Volumetric fluid flow is derived by a cross-correlation algorithm written in the C language. In vitro validation is performed with water in a flow bench. The computed flow (y) compared with the in-line-measured flow (x) yields the linear regression y = 1.024x - 0.157 (r = 0.99). The average coefficient of variation is less than 2% over a volumetric fluid flow range of 2 to 10 L/min.
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