Continuous Thermal Measurement of Cardiac Output

A thermal-dilution technique for the continuous measurement of cardiac output has been developed. It employs pulmonary-artery sensing of low-level periodic thermal signals generated in the right ventricle of the heart. A resistive element in a modified Swan Ganz®catheter is energized with a periodic...

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Bibliographic Details
Published in:IEEE transactions on biomedical engineering 1984-05, Vol.BME-31 (5), p.393-400
Main Authors: Philip, James H., Long, Michael C., Quinn, Michael D., Newbower, Ronald S.
Format: Article
Language:English
Subjects:
Arteries
Biological and medical sciences
Biomedical Engineering
Blood flow
Cardiac Output
Cardiovascular system
Frequency estimation
Heart
Humans
Instruments
Investigative techniques of hemodynamics
Investigative techniques, diagnostic techniques (general aspects)
Medical sciences
Signal generators
Signal processing
Signal to noise ratio
Thermistors
Thermodilution
Thermodynamics
Ventricular Function
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Summary:A thermal-dilution technique for the continuous measurement of cardiac output has been developed. It employs pulmonary-artery sensing of low-level periodic thermal signals generated in the right ventricle of the heart. A resistive element in a modified Swan Ganz®catheter is energized with a periodic electrical waveform. The resulting thermal signal is diluted by blood flow and attenuated by mixing within the heart. Sensed by a thermistor in the pulmonary artery, the thermal signal is processed by a microprocessor-based instrument using a suitable mathematical model. With multiple signal frequencies, separate estimates of the flow-dependent and mixing-dependent attenuation components become possible, allowing continuous monitoring of cardiac output. This technique works well in anesthetized, mechanically ventilated animals, even with average power levels as low as 4 W and corresponding temperature increases of a few hundredths of a degree centigrade. Based on measurements of pulmonary artery thermal noise spectra in humans, we infer that similar performance levels should be attainable with mechanically ventilated human subjects. However, noise spectra from spontaneously breathing critically ill patients suggest that signal-to-noise ratios would be less than satisfactory in that group unless increased signal power is allowed or improved algorithms are developed.
ISSN:0018-9294
1558-2531
DOI:10.1109/TBME.1984.325278