Abstract
Measurement of cardiac output is often investigated using a technique based on hot‐film anemometry. Here, we discuss a modification to hot‐film anemometry, which involves a cylindrical heating element mounted flush on the surface of a typical Swan‐Ganz catheter. In contrast to traditional thermodilution, the method discussed here has the potential to allow continuous monitoring of cardiac output.This paper demonstrates that there is a simple approximate relationship between the power input to the device to maintain a temperature of one degree above blood heat and cardiac output. Since, the heat transfer and the fluid flow decouple, a numerical model of the heat transfer of a cylindrical catheter (with heating element) sitting concentrically within a rigid cylindrical artery is developed. Numerical results were obtained for a wide selection of flow profiles, including experimental data. The results indicate that the cardiac output/power input relationship is extremely robust with respect to flow profile and system parameter variation.
Highlights
Cardiac output (CO), is the volume of blood passing through the heart in a given time
We have shown that the results obtained using pulsatile models of heat transfer in our simple cylindrical annular model differ from those using equivalent steady models
Using a flat velocity profile, the discrepancy between the steady and the pulsatile models was found to increase with increasing CO whereas this was not observed with the mixed profile whose unsteady part is a peaked profile
Summary
Cardiac output (CO), is the volume of blood passing through the heart in a given time. The CO should be around 4 or 5 l min but can drop to as low as 2 in critical situations It is an important diagnostic factor [1,2] during high risk surgery, transplantation, where it is used in conjunction with blood pressure to assess the performance of the heart. It is used post-operatively in intensive care. Clinicians have used thermodilution to measure CO [1] This involves inserting a catheter into the subclavian or jugular vein at the neck and feeding it through until it reaches the right atrium. The Stewart – Hamilton equations were originally used to predict CO from dye indicator methods [3] but suffer from many assumptions [4]
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