Blood warming apparatus

Fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature as it flows through a disposable flow system including a warming bag at flow rates variable over a substantial predetermined range, said apparatus comprising, in combination:

• housing means defining a heating chamber within the apparatus for receiving the warming bag;
• at least one electric heater element operable from an applied electric current for heating the fluid as it passes through the warming bag;
• control circuit means responsive to the input and output temperature of the fluid in the warming bag for generating a heater control signal providing an on-off duty cycle dependent on both the output temperature of the fluid and the differential between the input and output temperatures of the fluid;
• 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 elements and a source of electrical current and responsive to said heater control signal for controlling the application of current to the heating element in accordance with said control signal to maintain the output temperature of the fluid substantially constant at said predetermined nominal temperature notwithstanding variations in the flow rate thereof.

Fluid warming apparatus for heating a refrigerated fluid such as blood to a predetermined nominal temperature as it flows through a disposable flow system including a warming bag at flow rates variable over a substantial predetermined range, said apparatus comprising in combination:

• housing means defining a heating chamber within the apparatus for receiving the blood warming bag;
• at least one electrical heating element operable from an applied electrical current and disposed in thermal communication with the warming bag when the bag is seated within said heating chamber for heating the fluid as it passes through the warming bag;
• first temperature sensing means for sensing the input temperature of the fluid in said warming bag and developing a first output signal indicative thereof;
• second temperature sensing means for sensing the output temperature of the fluid within said bag and developing a second output signal indicative thereof;
• differential amplifier means for developing from said first and second output signals a differential signal indicative of the difference between said input and output temperatures;
• a ramp generator for generating a voltage ramp function having a slope which varies inversely with said differential signal;
• voltage comparison means for comparing said voltage ramp function with said second temperature-indicative output signal to generate a heater control signal providing a duty cycle which varies as a function of both the output temperature of the fluid and the differential between the input and output temperature of the fluid;
• and
• switch circuit means electrically connected between said heating element and a source of current and responsive to said heater control signal for controlling the application of current to said heating element in accordance with said control signal to maintain the output temperature of the fluid substantially constant at the predetermined nominal temperature notwithstanding variations in the flow rate thereof.