A tourniquet for occluding blood flow to a limb is improved by the addition of proximal and distal strain gauges. The proximal strain gauge may be monitored under conditions of total blood flow occlusion for time-varying signals indicative of volumetric limb changes arising from the subject's blood flow in the proximal section of the limb. Upon a change in limb occlusion pressure, the signals from the proximal strain gauge can be observed to change also, and the working pressure in the tourniquet can be adjusted safely in response. Automated control systems may further use inputs from a distal strain gauge and/or from a sensor that detects induced pressure changes within the tourniquet to improve the control of the tourniquet working pressure during operation to avoid unwanted blood flow past the tourniquet.