1. Doppler recordings were made from the brachial artery of healthy female subjects during a series of manoeuvres which altered the pressure—flow characteristics of the vessel.
2. Changes were induced in the peripheral circulation of the forearm by the application of heat or icepacks. A sphygmomanometer cuff was used to create graded occlusion of the vessel above and below the point of measurement. Recordings were also made whilst the subjects performed a standardized Valsalva manoeuvre.
3. The Doppler recordings were analysed both with the standard waveform indices (systolic/diastolic ratio, pulsatility index and resistance index) and by the method of Laplace transform analysis.
4. The waveform parameters obtained by Laplace transform analysis distinguished the different changes in flow conditions; they thus had direct physiological relevance, unlike the standard waveform indices.
