thermostromuhr

noun

ther·​mo·​strom·​uhr ˌthər-mō-ˈstrō-ˌmu̇(ə)r 

: a stromuhr that measures the rate of blood flow in an intact blood vessel by determining the amount of heating of the blood as indicated by a sensitive galvanometer when a radio-frequency current is passed through the vessel between thermocouples so that the amount of heating is inversely proportional to the rate of flow