An ultrasound control unit (10) is for coupling with an ultrasound transducer unit (12). The control unit is adapted to control a drive configuration or setting of the transducers of the transducer unit, each drive setting having a known power consumption level associated with it. The control unit includes a control module (20) adapted to adjust the drive setting from a first setting to a second setting, the second having a lower associated power consumption that the first. The second setting is tested by an analysis module (16), the analysis module adapted to determine a measure of reliability of ultrasound data acquired by the transducer unit, for the purpose of deriving at least one physiological parameter, when configured in the second setting. The second setting is only used if its determined reliability passes a pre-defined reliability condition.