 Wilbert Aarnoudse

Wilbert Aarnoudse is the named first author of a 2007 study validating direct volumetric blood flow measurement in coronary arteries by thermodilution. The method used continuous saline infusion, a 2.8-F infusion catheter and a 0.014-inch pressure/temperature-sensing guidewire. Validation included five dogs and 35 patients.^[ref]

The measurement uses a thermal tracer: a known inflow at a different temperature changes the downstream mixture temperature. An original two-stream model illustrates the principle. If blood and infused fluid have equal volumetric heat capacities, negligible heat exchange with the vessel and complete mixing,Here $Q_b,Q_i$ are volume flow rates, $T_b$ is baseline blood temperature, $T_i$ the infused-fluid temperature and $T_m$ the mixed temperature. This conservation calculation is not the clinical instrument's full calibration model.

For stipulated model inputs $Q_i=10$ mL/min, $T_b=37{}^{\circ }\mathrm{C}$, $T_i=25{}^{\circ }\mathrm{C}$ and $T_m=36.5{}^{\circ }\mathrm{C}$, the inferred blood flow is 230 mL/min. A small downstream temperature difference can therefore encode a larger flow, while also making the result sensitive to temperature offsets and incomplete mixing. Coronary thermodilution mixing assumptions matter independently of the precision of the temperature readout.

The primary study reports a canine comparison regression $Q_{\mathrm{thermo}}=0.73Q+42$ mL/min with $R^2=0.72$.^[ref] Association, calibration agreement and repeatability are different properties: a high association does not force slope one and intercept zero. The apparatus and validation comparisons make the credited work a measurement-method contribution, rather than a direct measurement of blood oxygen content or a general substitute for every coronary assessment.