= Wilbert Aarnoudse
{c}
\b[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.<Direct volumetric blood flow measurement in coronary arteries by thermodilution by Wilbert Aarnoudse and others>[Abstract, Methods]{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,
$$
Q_b(T_b-T_m)=Q_i(T_m-T_i),\qquad
Q_b=Q_i\frac{T_m-T_i}{T_b-T_m}.
$$
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 $Q_{\rm thermo}=0.73Q+42$ mL/min with $R^2=0.72$.<Direct volumetric blood flow measurement in coronary arteries by thermodilution by Wilbert Aarnoudse and others>[Abstract, Results]{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.
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