Measurement of Muscle Blood Flow in the Human Forearm with Radioactive Krypton and Xenon.

IN 1949 Kety proposed that if the rate of removal from the site of injection of an intramuscularly injected radioactive isotope was limited principally by flow, then the clearance of the tracer from the injection site could be used to measure local blood flow.' In the past, sodium-24 or iodine-131 has been used for this purpose, but with considerable variability in the results obtained in serial studies of the same persons.2 The chemically inert gases krypton-85 and xenon-133 have certain advantages over Na24 and I 131. They are chemically and physiologically inert; they are not normally present in the body; and they are rapidly excreted from the body via the lungs.3 The long physical half-life of Kr 85 ( 10.3 years) and the half-life of Xe'33 (5.27 days) make the use of these nuclides more convenient than Na 24 (15 hours). Finally, the lower gamma ray energies of Kr85 (0.513 mev) and Xe'33 (0.081 mev) are more suitable for external radiation detection than the high energy of Na24 (1.368 mev), which is difficult to localize accurately in the body. Accordingly, blood flow to forearm muscle was estimated by external monitoring of the rate of disappearance of radioactivity following intramuscular injection of an aqueous solution of Kr85 or Xe 33