Interpretation of tracer washout curves from a population of muscle fibers.

Consideration is given to the role of a population of muscle fibers of distributed diameters in the observed washout of a tracer, with particular reference to radioisotopic K and muscle fibers. It is concluded that if washout of tracer from a single fiber is described as first order, then washout of tracer from a population of fibers is apt to appear as first order.