Effects of time-varying flow and volume on cardiac output estimation from isotope dilution and residue detection
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Measurements of cardiac output from indicator dilution are subject to error when tracer is sampled at a constant rate but flow varies periodically. Using a pulsatile compartmental representation of a segment of the central circulation, we have examined the effect of time-varying flow and volume on determinations of cardiac output from isotope dilution and region-of-interest residue detection. The effects of input function dispersion, amplitude of flow variation, relative duration of systole, and injection directly into and proximal to a region-of-interest were studied. In contrast to distal concentration sampling where errors for comparable injection and flow characteristics are minimal at cardiac frequencies, errors from residue detection procedures can be as high as 15 to 20%, and depend on the region-of-interest, injection timing, and system parameters. Errors decrease with peripheral injection, increased dispersion of the input function, increased fractional duration of systole, and reduced amplitude of flow variation. Specific procedures for minimizing errors due to time-varying flow are discussed.
KeywordsCardiac Output Input Function Injection Timing Isotope Dilution Flow Variation
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