An IPC device (Vadoplex, OPED UK, UK) was fitted to each foot as per the manufacturer's instructions and activated for ten minutes prior to recording venous flow. The IPC provides a pump inflation pressure of 120mmHg, inflating once every 20 seconds. Each inflation was maintained for approximately 1 second, before deflation occurred. The maximum recording duration of the ultrasound scanner was 14 seconds. In order to capture 20 seconds of data, two contiguous measurements of 14 and 6 seconds were made. The machine records flow within the vessel. Since flow varies within the vessel, the machine is able to use a complex algorithm to sample velocities and flow over time and hence calculate the mean. In order to calculate mean velocity and volume flow over a complete 20 second cycle, we used the following equation: