Continuous measurement of flow rate and volume in the nanoliter range

A simple transducer which is based on changes of electrical capacity with volume is described. The system accomodates fluid volumes of several microliters and the resolution is below one nanoliter. The response time of the transducer is about 10 ms. The system is applicable for continuous recording of flow rates in renal collecting tubules. Pulsatile flow in the duct of Bellini is demonstrated.