Method and apparatus for controlling the inner temperature of a patient

Abstract

The invention relates to a method and apparatus for controlling the inner temperature of a patient, comprising the steps of creating a fluid circuit that comprises a patient and a heat exchanger, the power supply thereto being controlled by a controller; subjecting at least a portion of the fluid in said circuit to the heat exchanger; directing the subjected fluid to and into the patient to control the temperature of the patient; estimating the organ temperature of the patient by a model that has been obtained on a mammal other than the patient; and controlling the power supply to the heat exchanger such that the estimated organ temperature does not exceed a threshold organ temperature, potentially taking into account estimated future organ temperatures. The invention further relates to a method and apparatus for controlling the inner temperature of a patient when subject to whole body hyperthermia, and to a method for obtaining the model.

Claims

1. A method for controlling the inner temperature of a patient, the method comprising the steps of: creating a fluid circuit that comprises the patient and a heat exchanger, a power supply thereto being controlled by a controller; subjecting at least a portion of a fluid in said fluid circuit to the heat exchanger; directing the subjected fluid to and into the patient to control the inner temperature of the patient; estimating a temperature of an organ of the patient at a time t by a model comprising a parametric correlation function of the temperature of the organ and a number of input parameters, wherein the parametric correlation function, including a calibration of the parameters of the correlation function, has been obtained on an animal other than the patient; and controlling the power supply to the heat exchanger such that the estimated organ temperature remains below an upper threshold organ temperature and/or above a lower threshold organ temperature, wherein the parametric correlation function for one temperature sensor i is given by one of the following:
T.sub.organ(t)=C.sub.i+f.sub.skin.Math.T.sub.skin+f.sub.i.Math.T.sup.i.sub.sensor+1/Mf.sub.j.Math.P(t.sub.j)(I) wherein T.sub.organ (t)=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); f.sub.skin=a parameter constant (); T.sub.skin=the measured skin temperature ( C.); f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); M=body mass of the animal (kg); f.sub.j.Math.P(t.sub.j)=a weighted sum of heat outputs of the heat exchanger in time intervals t.sub.j=t.sub.jt.sub.j-1 to prior to time t with f.sub.j=parameter constant for each j.sub.th time interval;
T.sub.organ(t)=C.sub.i+f.sub.i*T.sup.i.sub.sensor+1/Mf.sub.j.Math.Q(t).Math.(T.sub.finT.sub.fout)dt(II) wherein T.sub.organ(t)=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); M=body mass of the animal (kg); f.sub.j.Math.Q(t).Math.(T.sub.finT.sub.fout) dt=the integral from t.sub.j to t.sub.j-1 of the product of the fluid flow Q (in m.sup.3/sec) and the temperature difference between a measured temperature T.sub.fin of the fluid ( C.) when entering the body and a measured temperature T.sub.fout of the fluid ( C.) when exiting the body in time intervals t.sub.j=t.sub.jt.sub.j-1 to prior to time t with f.sub.j=parameter constant for each j.sub.th time interval; or
T.sub.organ(t)=C.sub.i+T.sub.estimate(0)+f.sub.i.Math.(T.sup.i.sub.sensorT.sup.i0.sub.sensor)+1/Mf.sub.j.Math.P(t.sub.j)(III) wherein T.sub.organ (t)=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); T.sub.estimate (0)=the estimated organ temperature at time 0; f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); T.sup.i0.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.) at time 0; M=body mass of the animal (kg); f.sub.j.Math.P(t.sub.j)=a weighted sum of heat outputs of the heat exchanger in time intervals t.sub.j=t.sub.jt.sub.j-1 to prior to time t with f.sub.j=parameter constant for each j.sub.th time interval.

2. The method according to claim 1, wherein the patient is subject to whole body hyperthermia.

3. The method according to claim 1, wherein the input parameters comprise a temperature of at least one body part of the patient other than the organ, and power supplied to the heat exchanger prior to time t, wherein the at least one body part comprises the bladder, the skin, left tympanic, right tympanic, anus, pulmonary arteries, femoral veins, and/or esophagus.

4. The method according to claim 1, wherein the input parameters comprise the temperature of at least five body parts of the patient other than a skin.

5. The method according to claim 1, wherein the input parameters comprise the body mass of the patient.

6. The method according to claim 1, wherein the power supply to the heat exchanger is discontinued at a time t and a future organ temperature after time t is estimated from the power supplied to the heat exchanger prior to time t.

7. The method according to claim 1, wherein the organ temperature at a time t is estimated by deriving the organ temperature at time t for each input parameter, and taking an arithmetic mean of the derived organ temperatures for all input parameters to obtain the estimated organ temperature, wherein the arithmetic mean does not include the highest and the lowest value of the derived organ temperatures for each temperature measured.

8. The method according to claim 1, wherein the parametric correlation function for one temperature sensor i is given by:
T.sub.organ(t)=C.sub.i+f.sub.skin.Math.T.sub.skin+f.sub.i.Math.T.sup.i.sub.sensor+1/Mf.sub.j.Math.P(t.sub.j) wherein T.sub.organ=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); f.sub.skin=a parameter constant (); T.sub.skin=the measured skin temperature ( C.); f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); M=body mass of the animal (kg); f.sub.j.Math.P(t.sub.j)=a weighted sum of heat outputs of the heat exchanger in time intervals t.sub.j=t.sub.jt.sub.j-1 prior to time t with f.sub.j=parameter constant for each j.sub.th time interval.

9. The method according to claim 1, wherein the parametric correlation function for one temperature sensor i is given by:
T.sub.organ(t)=C.sub.i+f.sub.i*T.sup.i.sub.sensor+1/Mf.sub.j.Math.Q(t).Math.(T.sub.finT.sub.fout)dt wherein T.sub.organ=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); M=body mass of the animal (kg); f.sub.j.Math.Q(t).Math.(T.sub.finT.sub.fout)dt=the integral from t.sub.j to t.sub.j-1 of the product of the fluid flow Q (in m.sup.3/sec) and the temperature difference between a measured temperature T.sub.fin of the fluid ( C.) when entering the body and a measured temperature T.sub.fout of the fluid ( C.) when exiting the body in time intervals t.sub.j=t.sub.jt.sub.j-1 prior to time t with f.sub.j=parameter constant for each j.sub.th time interval.

10. The method according to claim 1, wherein the parametric correlation function for one temperature sensor i is given by:
T.sub.organ(t)=C.sub.i+T.sub.estimate(0)+f.sub.i.Math.(T.sup.i.sub.sensorT.sup.i0.sub.sensor)+1/Mf.sub.j.Math.P(t.sub.j) wherein T.sub.organ (t)=organ temperature at time t; C.sub.i=a parameter constant for sensor i ( C.); T.sub.estimate (0)=the estimated organ temperature at time 0; f.sub.i=a parameter constant () for the i.sub.th temperature sensor; T.sup.i.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.); T.sup.i0.sub.sensor=the measured temperature of the i.sub.th temperature sensor ( C.) at time 0; M=body mass of the animal (kg); f.sub.j.Math.P(t.sub.j)=a weighted sum of heat outputs of the heat exchanger in time intervals t.sub.j=t.sub.jt.sub.j-1 prior to time t with f.sub.j=parameter constant for each j.sub.th time interval.

11. A method according to claim 1, wherein the parametric correlation function, including a calibration of the parameters of the correlation function, has been obtained on an animal other than the patient by the following method steps comprising creating a fluid circuit that comprises the animal and a heat exchanger, a power supply thereto being controlled by a controller; controlling the heat exchanger to a set temperature profile; subjecting at least a portion of a fluid in said circuit to the heat exchanger; directing the subjected fluid to and into the animal to change the temperature of the animal; measuring corresponding input parameters comprising the temperature of at least one body part of the animal at a time t, and the power supplied to the heat exchanger prior to time t; measuring the temperature of an organ of the animal at the time t, wherein the organ corresponds to the patient organ for which the temperature is to be estimated; establishing a parametric correlation function between an estimated temperature of the organ of the animal and the input parameters measured on the animal; and determining the model parameters of the parametric correlation function such that the difference between the estimated brain temperature calculated with the correlation function and the measured temperature of the organ is minimized.

12. A method according to claim 1, wherein the organ of the patient comprises the brain.

Description

(1) The present invention is further elucidated on the basis of the non-limitative exemplary embodiment shown in the following FIGURES. Herein shows:

(2) FIG. 1 a schematic representation of an apparatus in accordance with the present invention

(3) FIG. 1 shows an apparatus (1) for controlling the temperature in a patient (2), comprising two catheters (3,4), one (3) for blood exiting the patient, and one (4) for returning the blood to the patient, for creating a fluid circuit (5) external to the patient; a pump (6) in association with said catheters, for pumping the fluid; a heat exchanger (7) through which said fluid circuit flows; and a controller (8), arranged to control the heater exchanger. In accordance with the invention, the controller controls the heat exchanger based on an estimated brain (9) temperature.

(4) The temperature of the brain is estimated based on temperature measurements on multiple locations on the patient, comprising, in this example, four temperature sensors (10, 11, 12, 13) located at the left tympanic (10), right tympanic (11), the bladder (12) and the skin (13). The temperature sensors can feed the measured temperatures to the controller to obtain the estimated brain temperature.

(5) Calibration Method

(6) The following method according to the invention was performed wherein the heat exchanger was a heater, and the organ was the brain. A pig was subjected to a method in which a fluid circuit was created comprising the pig and a heater, the power supply thereto being controlled by a controller, by using the apparatus of FIG. 1. The heater was controlled to a set temperature profile, and the fluid in the circuit heated by the heater. The heated fluid was then directed to and into the pig to change the temperature of the pig. Input parameters comprising the skin temperature of the pig at a time t, the temperature of selected body parts of the pig other than the skin temperature, and the power supplied to the heater prior to time t were measured at discrete intervals. A temperature sensor was applied to the pig's brain to measure the brain temperature continuously at different times t.

(7) The following parametric correlation function between an estimated brain temperature of the animal and the input parameters measured on the animal was established:
T.sub.brain(t)=C.sub.i+f.sub.skin*T.sub.skin+f.sub.i*T.sup.i.sub.sensor+1/Mf.sub.j*P(t.sub.j)

(8) The parameters of the parametric correlation function were calculated such that the difference between the estimated brain temperature calculated with the correlation function and the measured brain temperature is minimized.

(9) The following parameter values were obtained:

(10) C.sub.i=9.6362 ( C.);

(11) f.sub.skin=0.03 ();

(12) f.sub.i=0.7296 ( C.);

EXAMPLE 1

(13) The obtained parameters were used in the above mentioned function and applied to a situation wherein a patient was subjected to the same method as the pig, except for the placement of the sensor inside the brain. The temperature of the patient was measured on the skin and one other location.

(14) The following values are measured by sensors during whole body hyperthermia of the patient:

(15) T.sub.skin=40.2305 ( C.);

(16) T.sup.i.sub.sensor=42.9612 ( C.);

(17) The mass of the patient was 65.0 kg.

(18) 4 prior heat outputs were considered in the weighted sum of the parametric function, wherein the time intervals of 60 seconds were used:

(19) f.sub.1=0.0192 with a P(0-60) of 3.2756 kJ

(20) f.sub.2=0.0072 with a P(60-120) of 1.133 kJ

(21) f.sub.3=0.0111 with a P(120-180) of 94.400 kJ

(22) f.sub.4=0.0240 with a P(180-240) of 157.1333 kJ

(23) When all these values are entered in the function, the estimated brain temperature based on one sensor besides the skin temperature sensor is 42.26 C. The controller may, based on this value and given that this value is below the threshold value of 43 C., determine if more power should be supplied to the heater to increase the body temperature of the patient.

EXAMPLE 2

(24) In this example the organ was again the brain, and the heat exchanger was set up to be a heater. An estimation of the future brain temperature will be described. The future brain temperature can be a measure to estimate if threshold values are exceeded if power supply to the heater is discontinued for a certain amount of time. Because it takes a certain amount of time before the heat supplied by the heater affects the brain temperature, the expected future brain temperature depends on the added heat before that time.

(25) If from time t no more heat is supplied to the heater, the same function as derived in the calibration method can be used to determine the expected brain temperature in the future, with a small alteration in the weighted sum of heat outputs (1/Mf.sub.j*P(t.sub.3)).

(26) The 4 prior heat outputs of Example 1 will shift one position, since the future brain temperature is estimated.

(27) In the weighted sum the time intervals then become the following:

(28) f.sub.1=0.000 with a P(0-60) of 0 (heater was switched off, weighing factor is irrelevant now, anything multiplied with zero becomes zero)

(29) f.sub.2=0.0072 with a P(0-60) of 3.2756 kJ (f.sub.1 of example 1)

(30) f.sub.3=0.0111 with a P(60-120) of 1.133 kJ (f.sub.2 of example 1)

(31) f.sub.4=0.0240 with a P(120-180) of 94.400 kJ (f.sub.3 of example 1)

(32) The other values remain the same, yielding an estimated future brain temperature of 42.22 C., based on previous added heat and when heating is switched off for one period of time.