Abstract: Medical diagnostic apparatus suitable for screening use in the detection of deep veinous thrombosis in association with hip joint replacement comprises a thigh cuff (12) inflatable and deflatable to constrict and release venous blood flow in the relevant leg, a processor (10) operable automatically to control deflation of the cuff in a predetermined manner following inflation to inhibit venous flow, and a strain gauge (13) engageable around the leg below the cuff and operable to provide a signal representing venous flow caused by the controlled deflation. The deflation control is preferably effectively instantaneous by way of a solenoid valve (15) of appropriately high air flow capability.