Abstract
A simple algorithm for detecting and flagging the start of the systolic upstroke or 'pulse foot' of Doppler ultrasound waveforms is described. It operates in three stages. It first locates the true maximum of each waveform, it then works back to the point of maximum gradient on the upslope of the waveform, and finally works back to the maximum rate of change of gradient at the foot of the waveform. The algorithm has been used to process the Doppler signals from over 150000 individual cardiac cycles and has only been completely defeated by signals which, on review, have been considered too noisy for further analysis.