Effect of hematocrit on the washout of xenon and iodantipyrine from dog myocardium.

The rates of washout of 133Xe and 131I-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/kI), which is a measure of the ratio of the dynamic blood-tissue partition coefficients (lambdabIX/lambdabtI), increases linearly with hematocrit. This dynamic lambdabt ratio has almost the same relationship to hematocrit as the static lambdabt ratio. By the use of appropriate hemotocrit-specific lambdabt 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 measurement in the dog with 133Xe 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 131I-iodanatipyrine washout had negligible errors.