Effect of Hematocrit on the Washout of Xenon and Iodoantipyrine from Dog Myocardium

The rates of washout of m X e and I-iodoantipyrine from the myocardium into the coronary sinus blood were determined over a wide range of hematocrits after simultaneous injection of the isotopes into the left anterior descending coronary artery of dogs. The ratio of the monoexponential disappearance constants (kx/k,), which is a measure of the ratio of the dynamic blood-tissue partition coefficients (Xb,x/XbtI), increases linearly with hematocrit. This dynamic XbI ratio has almost the same relationship to hematocrit as the static Xbt ratio. By the use of appropriate hemotocrit-specific Xb, values, we found that simultaneous blood flows calculated from the two indicators with different disappearance constants showed excellent agreement. If this hematocrit-dependent alteration in indicator partitioning is neglected, blood flow measurements in the dog with Xe washout may introduce an error of approximately 1.15% per unit hematocrit deviation from the normal value (taken as 45%), whereas blood flow measurements with ' "I-iodoantipyrine washout had negligible errors.