microplethysmography

The technique of measuring minute changes in the volume of a part as a result of blood flow into or out of it.

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mi·cro·pleth·ys·mog·ra·phy (mi″kro-pleth″is-mogґrə-fe) [micro- + plethysmography] the recording of minute changes in the size of a part as produced by the circulation of blood in it.