Periodic microflow pattern measured with a new microflow probe within the rat kidney cortex

With a newly developed microflow probe of high spatial resolution periodic changes of flow occurring within a tissue sphere of a radius of less than or equal to 50 micrometer have been observed. The frequency distribution of the periodic changes of flow was similar to the frequencies observed earlier with different techniques in the same preparation and in other organs (Basar and Weiss, 1970; Weiss and Thiemann, 1973). Preferred frequencies were: 0.02 Hz, 0.06 Hz and 0.1 Hz. Manufacture, calibration, the complete setup, and the estimation of the power of spatial resolution of the microflow probe are described. Periodic heating of the flow-sensing thermocouple at the tip of the probe (luminal diameter less than or equal to 10 micrometer) obviates the use of a reference thermocouple, renders the system (relatively) insensitive against uncontrolled changes of ambient temperature, and thus allows measurements with a very high sensitivity.