cryogen is reutilized and extends the operation time even longer in another embodiment the medical device 30 may provide a system which is controlled through a series of computer controlled valves including any heaters sensors motors or gauges the sensors control and monitor pressure temperature and fluid level in the dewar and can measure any metric as may be desired in one aspect the sensors monitor pressure levels within defined safety ranges in another aspect the sensors may control the pressurization of one or more components internal to the dewar any of the valves 2 7 8 9 27 or 32 including exit portal valve 14 may be automated to enable a controlled and consistent operation of the cryogenic system e g computer controlled operation through the electronically controlled valves an embodiment of a system 50 is shown in fig4 as illustrated in a top view of the system 50 a series of six pulsatile pressurization chambers 40 are sealed chambers cylinders 40 within dewar 6 of the closed system 50 from the pump liquid cryogen in pumped to the pulsatile pressurization chambers 40 which then delivers liquid cryogen in a continuous series of bursts to the heat exchanger 4 the baffled linear heat exchanger 4 provides an enhanced subcooling of the pressurized liquid cryogen while also incorporating an integral subcooling unit 3 the chambers 40 each comprising an individual immersion heater 44 can then.