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Blood warming apparatus

  • US 4,167,663 A
  • Filed: 01/24/1977
  • Issued: 09/11/1979
  • Est. Priority Date: 01/24/1977
  • Status: Expired due to Term
First Claim
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1. Fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature prior to infusion at flow rates variable over a substantially predetermined range, said apparatus comprising, in combination:

  • housing means defining a heating chamber for the fluid within the apparatus, the fluid having an input temperature and an output temperature within said chamber;

    at least one electric heater element operable from an applied electric current in thermal communication with the fluid in said heating chamber for heating the fluid as it passes through the apparatus;

    control circuit means responsive to said input and output temperatures of the fluid for generating a heater control signal dependent on both said output temperature and flow rate of the fluid;

    said control circuit means including first temperature sensing means for sensing the input temperature of the fluid and developing a first output signal indicative thereof, second temperature sensing means for sensing the output temperature of the fluid and developing a second output signal indicative thereof, a differential amplifier for developing from said first and second output signals a differential signal indicative of the differential between said input and output temperatures;

    said heater control signal being variable as a function of both said output temperature of the fluid and said differential signal; and

    switch circuit means electrically connected between said heating element and a source of electrical current, and responsive to said heater control signal for controlling the application of current to said heating element, for maintaining the fluid at the predetermined nominal temperature notwithstanding variations in the flow rate thereof.

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