Optimising the Windkessel Model for Cardiac Output Monitoring During Changes in Vascular Tone

Peter Charlton, John Smith, Luigi Camporota, Richard Beale, Jordi Alastruey

Research output: Chapter in Book/Report/Conference proceedingPoster abstract

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INTRODUCTION. Algorithms for estimating cardiac output (CO) from the arterial blood pressure wave have been observed to be inaccurate during changes in vascular tone. Many such algorithms are based on the Windkessel model of the circulation. We investigated the optimal analytical approaches and assumptions to apply this model for CO estimation during changes in vascular tone.

METHODS. Equations relating CO to the measured arterial blood pressure were derived by applying conservation of mass and Pouiseille’s law to the Windkessel model. Analytical approaches and assumptions used in the literature were applied to these equations to construct CO algorithms. We evaluated these algorithms on data collected from 15 critically ill patients. The algorithms were calibrated with reference transpulmonary thermodilution CO measurements at baseline, and their accuracy was determined by comparison with reference measurements during a pharmacologically controlled change in vascular tone.

RESULTS. We found that the most accurate algorithms: (i) maintained the compliance and outflow terms in the Windkessel model; and (ii) re-calculated compliance on a beat-by-beat basis. They produced a percentage error of ±31%. In addition, algorithms had higher accuracy when the end of systole was identified using the zero crossing of the second derivative of pressure, and when the outflow pressure was assumed to be zero. The choice of methods for estimating compliance and the systemic time constant had little effect on accuracy.

CONCLUSION. We found large differences in the accuracy of CO algorithms based on the Windkessel model of the circulation during changes in vascular tone. Optimal analytical approaches and assumptions were identified from those tested. However, none of the tested algorithms was within the clinically acceptable accuracy of ±30%.

Original languageEnglish
Title of host publicationMEC Annual Meeting and Bioengineering14 Programme and Abstracts
Place of PublicationLondon
PublisherMECbioeng14, Imperial College London
Number of pages1
ISBN (Print)9780993039003
Publication statusPublished - 2014


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