Publications by authors named "Maartje C F Geven"

3 Publications

  • Page 1 of 1

Thermal anemometric assessment of coronary flow reserve with a pressure-sensing guide wire: an in vitro evaluation.

Med Eng Phys 2011 Jul 2;33(6):684-91. Epub 2011 Feb 2.

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

Assessment of coronary flow reserve (CFR) with a commercially available pressure-sensor-tipped guide wire using the principle of thermal anemometry could provide major clinical benefits both in determining and in distinguishing between epicardial and microvascular coronary artery disease. In constant-temperature thermal anemometry, the electrical power required to maintain an element at a constant temperature is a measure for the local shear rate. Here, the feasibility of applying this thermoconvection method to a pressure-sensing guide wire is investigated using an in vitro model. A theoretical relation between electrical power and steady shear rate based on boundary layer theory was tested in an experimental set-up. In steady flow, a reproducible relation between electrical power and shear rate was obtained with an overheat temperature of 20K, which was in good agreement with theory. The relation between shear rate and flow, however, depends on geometry of the artery and position of the guide wire inside the vessel. Although this means that this thermoconvection method is less useful for absolute flow measurements, CFR could be assessed even for unsteady flow using the steady calibration curve with a mean relative difference of (3±5)% compared to CFR derived from the golden standard using an ultrasonic flow measurement device.
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http://dx.doi.org/10.1016/j.medengphy.2011.01.004DOI Listing
July 2011

Continuous infusion thermodilution for assessment of coronary flow: theoretical background and in vitro validation.

Med Eng Phys 2009 Jul 23;31(6):688-94. Epub 2009 Feb 23.

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

Direct volumetric assessment of coronary flow during cardiac catheterization has not been available so far. In the current study continuous infusion thermodilution, a method based on continuous infusion of saline into a selective coronary artery is evaluated. Theoretically, volumetric flow can be calculated from the known infusion rate (Q(i)), the temperatures of the blood (T(b)), the saline (T(i)), and the mixture downstream to the infusion site (T). We aimed to validate and optimize the measurement method in an in vitro model of the coronary circulation. Full mixing of infusate and blood was found to be the main prerequisite for accurate determination of the coronary flow. To achieve full mixing the influence of catheter design, infusion rate, and location of temperature measurement were assessed. We found that continuous infusion thermodilution slightly overestimated coronary flow determined by directly measured reference flow by 7+/-8%, over the entire physiological flow range of 50-250 ml/min. These results were found using a specially designed infusion catheter (infusion mainly through distally located sideholes), a high enough infusion rate (25 ml/min), and measurement of the mixing temperature between 5 and 8 cm distal from the tip of the infusion catheter. Absolute coronary flow rate can be measured reliably by the continuous infusion method when full mixing is present, under the conditions mentioned above.
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http://dx.doi.org/10.1016/j.medengphy.2009.01.006DOI Listing
July 2009

A physiologically representative in vitro model of the coronary circulation.

Physiol Meas 2004 Aug;25(4):891-904

Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.

With the development of clinical diagnostic techniques to investigate the coronary circulation in conscious humans, the in vitro validation of such newly developed techniques is of major importance. The aim of this study was to develop an in vitro model that is able to mimic the coronary circulation in such a way that coronary pressure and flow signals under baseline as well as hyperaemic conditions are approximated as realistically as possible and are in accordance with recently gained insights into such signals in conscious man. In the present in vitro model the heart, the systemic and coronary circulation are modelled on the basis of the elements of a lumped parameter mathematical model only consisting of elements that can be represented by segments in an experimental set-up. A collapsible tube, collapsed by the ventricular pressure, represents the variable resistance and volume behaviour of the endocardial part of the myocardium. The pressure and flow signals obtained are similar to physiological human coronary pressure and flow, both for baseline and hyperaemic conditions. The model allows for in vitro evaluation of clinical diagnostic techniques.
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http://dx.doi.org/10.1088/0967-3334/25/4/009DOI Listing
August 2004
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