In a case of RA the synovitis and the pannus can be examined using ultrasound. The activity of the condition registers as a halo around the flexor tendons of the fingers which sends off fewer echoes. Peripheral resistance (expressed in terms of Pourcelot's ratio) falls where clinical activity in the joints is higher. Correspondingly, values of Pourcelot's ratio are normal or higher than usual in the case of inactive joint processes. Diagnostic signs for PSS are very high values of Pourcelot's ratio and a closed "systolic window". After the hands have been warmed (for 5 min in a bath of water at 40 degrees C) the systolic window is "opened" in cases of a functional disruption in the blood supply, whereas in cases of advanced PSS the blood vessels are observed to be rigid with high peripheral resistance.