Bone blood flow measured with microspheres: the problem of non-entrapment.

Radioactive microspheres were injected into the tibial nutrient arteries of dogs. The validity of their use to measure bone blood flow was tested by examining their concentration in femoral venous blood. Non-entrapment in the tibia was considerable in two animals following rather prolonged alternate periods of perfusion and ischaemia. When such treatment was minimised, non-entrapment was small, showing that in this respect microspheres provide a valid means of measuring bone blood flow.