You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Outcome", "Participant", "Intervention"].

Please return the output as a JSON object of the format: {"Participant" : ["patients with COPD", ...], "Intervention" : ["Atenolol", ...], "Outcome" : ["blood pressure", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

High-pressure , rapid-inflation pneumatic compression improves venous hemodynamics in healthy volunteers and patients who are post-thrombotic . PURPOSE Deep vein thrombosis ( DVT ) is a preventable cause of morbidity and mortality in patients who are hospitalized . An important part of the mechanism of DVT prophylaxis with intermittent pneumatic compression ( IPC ) is reduced venous stasis with increased velocity of venous return . The conventional methods of IPC use low pressure and slow inflation of the air bladder on the leg to augment venous return . Recently , compression devices have been designed that produce high pressure and rapid inflation of air cuffs on the plantar plexus of the foot and the calf . The purpose of this study is to evaluate the venous velocity response to high-pressure , rapid-inflation compression devices versus standard , low-pressure , slow-inflation compression devices in healthy volunteers and patients with severe post-thrombotic venous disease . METHOD Twenty-two lower extremities from healthy volunteers and 11 lower extremities from patients with class 4 to class 6 post-thrombotic chronic venous insufficiency were studied . With duplex ultrasound scanning ( ATL-Ultramark 9 , Advanced Tech Laboratory , Bothell , Wash ) , acute DVT was excluded before subject evaluation . Venous velocities were monitored after the application of each of five IPC devices , with all the patients in the supine position . Three high-pressure , rapid-compression devices and two standard , low-pressure , slow-inflation compression devices were applied in a random sequence . Maximal venous velocities were obtained at the common femoral vein and the popliteal vein for all the devices and were recorded as the mean peak velocity of three compression cycles and compared with baseline velocities . RESULTS The baseline venous velocities were higher in the femoral veins than in the popliteal veins in both the volunteers and the post-thrombotic subjects . Standard and high-pressure , rapid-inflation compression significantly increased the popliteal and femoral vein velocities in healthy and post-thrombotic subjects . High-pressure , rapid-inflation compression produced significantly higher maximal venous velocities in the popliteal and femoral veins in both healthy volunteers and patients who were post-thrombotic as compared with standard compression . Compared with the healthy volunteers , the patients who were post-thrombotic had a significantly attenuated velocity response at both the popliteal and the femoral vein levels . CONCLUSION High-pressure , rapid-inflation pneumatic compression increases popliteal and femoral vein velocity as compared with standard , low-pressure , slow-inflation pneumatic compression . Patients with post-thrombotic venous disease have a compromised hemodynamic response to all IPC devices . However , an increased velocity response to the high-pressure , rapid-inflation compression device is preserved . High-pressure , rapid-inflation pneumatic compression may offer additional protection from thrombotic complications on the basis of an improved hemodynamic response , both in healthy volunteers and in patients who were post-thrombotic .
{"Intervention": ["duplex ultrasound scanning", "Three high-pressure , rapid-compression devices and two standard , low-pressure", "High-pressure , rapid-inflation pneumatic compression", "slow-inflation compression devices"], "Outcome": ["rapid-inflation compression", "hemodynamic response", "popliteal and femoral vein velocities", "Standard and high-pressure", "maximal venous velocities", "velocity response", "popliteal and femoral vein velocity", "popliteal and femoral veins"], "Participant": ["healthy volunteers and patients who are post-thrombotic ."]}