Body temperature measurement devices, methods, and systems
A core temperature measurement may be made by varying the heat transfer dynamics of a blood circuit and fitting parameters of a blood circuit heat transfer configuration to measurements under the varied conditions. Then the input temperature of the patient core can be extracted from the model and a current temperature measurement remote from the patient core and optionally other measurements such as blood flow rate.
1. A method of calculating a blood return temperature, comprising:
pumping blood from a patient using an extracorporeal blood processing machine, the pumping including pumping blood at multiple flow rates;
measuring blood temperatures in a blood circuit at a temperature sensor located remote from a patient access, connected by an arterial portion of the patient access, for each of said multiple flow rates, and recording the measured blood temperature;
calculating a heat transfer characteristic of the blood circuit from the patient access to the temperature sensor based on the multiple flow rates and the recorded measured blood temperatures;
using the heat transfer characteristic, regulating a return temperature at a patient access end of a venous portion of said blood circuit that returns blood to said patient.
2. The method of claim 1 , wherein the regulating is effective to maintain a body temperature of a patient in a predefined range.
3. The method of claim 1 , wherein the regulating includes compensating for heat transfer in said venous portion between blood carried thereby and an ambient environment within which the venous portion is located.
4. The method of claim 1 , further comprising:
detecting a condition indicating that said heat transfer characteristic has changed and, responsively thereto, repeating said pumping blood at multiple flow rates and calculating a heat transfer characteristic responsively to a result of the detecting.
5. The method of claim 4 , wherein the detecting a condition includes a predefined change in a temperature indicated by the temperature sensor.
6. The method of claim 4 , wherein the detecting includes detecting a mechanical movement of the blood circuit.
7. The method of claim 1 , further comprising:
detecting a steady state of said heat transfer characteristic, wherein the recording is responsive to said detecting a steady state.
8. A system for performing a blood treatment, comprising:
a blood treatment machine adapted to receive a blood circuit and for pumping blood from a patient;
a controller connected to the blood treatment machine, the controller being programmed to pump blood at multiple flow rates during a predetermined operating mode;
during the predetermined operating mode, the controller measuring blood temperatures, and recording them, wherein the blood temperatures are measured in the blood circuit at a temperature sensor located remote from a patient access of said blood circuit, the patient access being connected by an arterial portion thereof to said temperature sensor, said blood temperatures being measured and recorded for each of said multiple flow rates;
the controller calculating a heat transfer characteristic of the blood circuit from the patient access to the temperature sensor responsively to the multiple flow rates and the blood temperatures, respectively;
the controller, responsively to the heat transfer characteristic, regulating a return temperature at a patient access end of a venous portion of said blood circuit that returns blood to said patient.
9. The system of claim 8 , wherein the regulating is effective to maintain a body temperature of a patient in a predefined range.
10. The system of claim 8 , wherein the regulating includes compensating for heat transfer in said venous portion between blood carried thereby and an ambient environment within which the venous portion is located.
11. The system of claim 8 , wherein the controller is further programmed for detecting a condition indicating that said heat transfer characteristic has changed and, responsively thereto, repeating said pumping blood at multiple flow rates and calculating a heat transfer characteristic responsively to a result of the detecting.
12. The system of claim 11 , wherein the detecting a condition includes a predefined change in a temperature indicated by said temperature sensor.
13. The system of claim 11 , wherein the detecting includes detecting a mechanical movement of the blood circuit.
14. The system of claim 8 , wherein the controller is further programmed for detecting a steady state of said heat transfer characteristic, wherein the recording is responsive to said detecting a stead state.