HEAT-FLOW SENSOR

Abstract

The invention describes a passive heat-flow sensor (1) comprising a contact face (11) for placement on a subject (8) during a temperature monitoring procedure; and a plurality of combined thermistor arrangements, wherein a combined thermistor arrangement comprises an inner thermistor (S1) arranged at an inner face of the sensor (1); an upper thermistor (S2) arranged at the upper surface of the sensor (1) and arranged relative to the inner thermistor (S1) to measure a vertical heat flow outward from the subject (8); and a lateral thermistor (S3) arranged relative to the inner thermistor (S1) to measure a horizontal heat flow along the contact face (11). The invention further describes a method of measuring the temperature of a subject (8) using a heat-flow sensor (1); and a temperature sensing arrangement (10) for monitoring the temperature of a subject (8) using a heat-flow sensor (1).

Claims

1. A passive heat-flow sensor comprising a contact face for placement on a subject during a temperature monitoring procedure; and a plurality of combined thermistor arrangements, wherein a combined thermistor arrangement comprises: an inner thermistor arranged at an inner face of the sensor; an upper thermistor arranged at the upper surface of the sensor and arranged relative to the inner thermistor to measure a vertical heat flow outward from the subject; and a lateral thermistor arranged in line with the inner thermistor to measure a horizontal heat flow along the contact face.

2. A passive heat-flow sensor according to claim 1, comprising at least four combined thermistor arrangements.

3. A passive heat-flow sensor according to claim 1, comprising a plurality of vertical thermistor pairs, wherein a vertical thermistor pair comprises an inner thermistor and an upper thermistor.

4. A passive heat-flow sensor according to claim 1, wherein the outer surface of the sensor is exposed.

5. A passive heat-flow sensor according to claim 1, realized as a passive dual heat-flow sensor and comprising a vertical thermistor arrangement with a further inner thermistor and a further upper thermistor arranged relative to that inner thermistor to measure a further vertical heat flow outward from the subject.

6. A passive heat-flow sensor according to claim 5, wherein the vertical thermistor arrangement is positioned centrally in the heat-flow sensor.

7. A method of measuring the temperature of a subject using a passive heat-flow sensor according to claim 1, which method comprises the steps of: placing the contact face of the passive heat-flow sensor on the subject during a temperature monitoring procedure; receiving temperature measurement values collected by the thermistors of the passive heat-flow sensor; and calculating the temperature of the subject on the basis of the received temperature measurement values.

8. A method according to claim 7, comprising the steps of comparing temperature measurement values of the combined thermistor arrangements of the passive heat-flow sensor to identify thermistors associated with a maximum vertical heat flow; identifying the neighboring combined thermistors; and calculating the temperature of the subject on the basis of the temperature measurement values of those thermistors.

9. A method according to claim 7, comprising the step of averaging one or more temperature measurement values prior to calculating the temperature of the subject.

10. A method according to claim 7, comprising the steps of: comparing temperature measurement values of the combined thermistor arrangements of the passive heat-flow sensor; identifying a combined thermistor arrangement providing unreliable temperature measurement values; and discarding temperature measurement values collected by that combined thermistor arrangement.

11. A temperature sensing arrangement for monitoring the temperature of a subject, comprising: a passive heat-flow sensor according to claim 7; and an evaluation unit arranged to receive temperature measurement values from the thermistors of the passive heat-flow sensor and to calculate the temperature of the subject on the basis of the received temperature measurement values.

12. A temperature sensing arrangement according to claim 11, wherein the passive heat-flow sensor comprises a wireless interface for transmitting temperature measurement values to the evaluation unit.

13. A temperature sensing arrangement according to claim 11, wherein the passive heat-flow sensor is realized as a wearable device.

14. A temperature sensing arrangement according to claim 11, wherein the evaluation unit is realized as a portable device.

15. A temperature sensing arrangement according to claim 1, incorporated in a patient support device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a schematic representation of a first embodiment of the inventive temperature sensing arrangement;

[0035] FIG. 2 shows a plan view of the heat-flow sensor of FIG. 1 from below;

[0036] FIG. 3 shows a plan view of the heat-flow sensor of FIG. 1 from above;

[0037] FIG. 4 shows temperature curves relating to the heat-flow sensor of FIG. 1;

[0038] FIG. 5 is a schematic representation of a second embodiment of the inventive temperature sensing arrangement;

[0039] FIG. 6 shows a plan view of the heat-flow sensor of FIG. 5 from below;

[0040] FIG. 7 shows a plan view of the heat-flow sensor of FIG. 5 from above, showing a middle level;

[0041] FIG. 8 shows a plan view of the heat-flow sensor of FIG. 5 from above, showing a top level;

[0042] FIG. 9 shows temperature regions relating to the sensor of FIG. 5;

[0043] FIG. 10 shows temperature development of enhanced thermistor configurations in an inventive sensor of the dual heat-flow type;

[0044] FIG. 11 is a schematic representation of a third embodiment of the inventive temperature sensing arrangement;

[0045] FIG. 12 shows a plan view of the heat-flow sensor of FIG. 11 from below.

[0046] In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] FIG. 1 shows a schematic cross-section through the inventive heat-flow sensor 1, realized in this exemplary embodiment as an enhanced single heat-flow sensor 1 of a temperature monitoring arrangement 10. This can be securely attached to the subject 8, for example to the skin of a patient 8. The outer surface 12 of the sensor is exposed to the surroundings and is not covered by any insulating material. A first thermistor S1 is arranged at an inner face of the sensor 1, and will lie in close contact to the patient's skin. A second thermistor S2 is arranged at the upper surface of the sensor 1. The thermal resistivity RV of the sensor 1 in the vertical direction, and the thermal resistivity RH of the sensor 1 in the horizontal direction are indicated by resistor symbols. A further resistor symbol indicates the thermal resistivity R.sub.B of the body 8 to which the sensor 1 is attached.

[0048] Obtaining a temperature measurement at any one point in time using the sensor 1 involves collecting the temperature measurement values T1, T2, T3 from the thermistors S1, S2, S3 respectively (i.e. thermistor S1 delivers temperature measurement value T1, thermistor S2 delivers temperature measurement value T2 etc.) and calculating a sensed temperature using knowledge of the heat flux through the sensor 1. To compute the sensed temperature using the enhanced single heat-flow sensor 1, it is also necessary to determine or estimate the thermal resistivity R.sub.B of the skin, which may vary from patient to patient. The sensed body temperature T.sub.db may be calculated using equation (1) as already described above. To this end, the measurement values collected by the thermistors S1, S2, S3 are sent to an evaluation unit 2 of the temperature monitoring arrangement 10, for example over a cable connection or wirelessly. A microprocessor 3 of the evaluation unit 2 performs the necessary computations to arrive at the body temperature. A display 4 can show core body temperature development as time progresses. While the diagram only indicates one lateral thermistor for the sake of simplicity, any number of lateral thermistors S3 and vertical thermistor pairs S1, S2 can be implemented by such an enhanced single heat-flow sensor.

[0049] FIG. 2 shows a plan view of such a sensor from below, showing the positions of an inner thermistor S1 and lateral thermistors S3 on the contact face 11 of the sensor 1. In this exemplary embodiment, the sensor 1 comprises a centrally positioned inner thermistor S1, and four equidistantly arranged lateral thermistors S3. FIG. 3 shows a plan view of the sensor 1 from above, indicating the position of the upper thermistor S2 of the enhanced thermistor configuration. The shape of the sensor does not have to be circular with a flat contact surface, as shown in the exemplary embodiments, but can be chosen to best fit the region on the body where the sensor is to be used.

[0050] FIG. 4 shows temperature curves obtained in a basic test setup, using a hotplate with a set point at 37 C., and a skin-like material with a thermal conductivity of 0.30 W/mK. A first curve 40 shows the temperature of the body measured using the inventive enhanced single heat-flow sensor, with a single enhanced thermistor arrangement. A second curve 41 shows the temperature measured using a conventional single heat-flow sensor (without any lateral compensation). The advantage of using the lateral thermistor can clearly be seen, since the temperature estimated using values provided by the enhanced thermistor arrangement reaches equilibrium faster, and is a closer match to the reference temperature.

[0051] FIG. 5 shows a schematic cross-section through a second embodiment of the inventive heat-flow sensor 1. Here, the sensor 1 comprises a lower layer and an upper layer, to achieve two different values of thermal resistivity RV, RV1 in the vertical or outward direction. The diagram shows an enhanced thermistor configuration with thermistors S1, S2, S3 as described in FIG. 1 above, and also an additional vertical thermistor configuration comprising a further inner thermistor SV1 and a further outer thermistor SV2. Here, thermistor SV1 delivers temperature measurement value TV1, and thermistor SV2 delivers temperature measurement value TV2. In this embodiment, the temperature measurement values T1, T2, T3 from the enhanced thermistor configuration and the temperature measurement values TV1, TV2 from the additional vertical thermistor configuration are sent to an evaluation unit 2, which can be realized in a hand-held device such as a smartphone or tablet computer with a display 4. A microprocessor 3 of the hand-held device can compute the body temperature T.sub.db using equations (2)-(5) as described above. In this exemplary embodiment, the sensor 1 comprises a wireless interface 5 for wireless transmission of the temperature measurement values T1, T2, T3, TV1, TV2 to the evaluation unit 2.

[0052] FIG. 6 shows a plan view from below of an enhanced dual-flow sensor 1 with four enhanced thermistor configurations about a central vertical thermistor configuration, indicating the position of the inner thermistor SV1 of the centrally positioned vertical thermistor configuration, the positions of the inner thermistors S1 and the lateral thermistors S3 of the four enhanced thermistor configurations. FIG. 7 shows a plan view from above the middle layer of the enhanced dual-flow sensor 1, indicating the positions of the upper thermistors S2 of the enhanced thermistor configurations. FIG. 8 shows a plan view from above the top layer of the enhanced dual-flow sensor 1, indicating the position of the upper thermistor SV2 of the centrally positioned vertical thermistor configuration. Temperature measurement values provided by the four enhanced thermistor configurations can be averaged to improve the accuracy of the sensed body temperature.

[0053] FIG. 9 shows a schematic representation of the temperatures corresponding to the thermistor arrangements of the enhanced dual-flow sensor of FIGS. 6-8. Here, the relative temperatures of the various thermistor arrangements are indicated as shaded regions 90, 91, 92 of a matrix. The intensity of the shading is interpreted relative to the remaining neutral regions of the matrix. The temperature measured by the vertical thermistor arrangement is indicated by the central shaded region 90. Temperatures measured using data provided by the inner and upper thermistors of the enhanced thermistor arrangements are indicated by the shaded regions 92, while the temperatures measured using data provided by the inner and lateral thermistors of the enhanced thermistor arrangements are indicated by the shaded regions 91. The darker color of the shaded region at the upper right in the diagram indicates that this thermistor is in poor contact with the patient's skin. The evaluation unit can identify such a discrepancy in the temperature measurement values, and can choose to ignore temperature measurement values from a thermistor configuration that appears to be delivering erroneous or unreliable data.

[0054] FIG. 10 shows an exemplary temperature development plot of the enhanced thermistor arrangements described in FIG. 9 above. Curve 10A is exemplary of a temperature calculated on the basis of temperature measurement values from three enhanced thermistor arrangements of which the inner thermistors are in good contact with the patient's skin. Curve 10B is exemplary of a temperature calculated on the basis of temperature measurement values from a fourth enhanced thermistor arrangement of which the inner thermistors are in poor contact with the patient's skin. Owing to the persistent significant difference in the values, the evaluation unit would disregard the values provided by the fourth enhanced thermistor arrangement from the temperature calculation algorithm.

[0055] The final estimated core body temperature depends to a large extent on the geometry and thermal conductivity of the sensor. Experimental results have shown that even during sub-optimal conditions, the enhanced sensor performs very well. When applied to a reference body that is gradually heated, the temperature sensed using data provided by an inventive enhanced single heat-flow sensor is a much closer match than the temperature sensed using data provided by the conventional single heat-flow sensor. Similarly, the temperature sensed by an enhanced dual heat-flow sensor according to the invention has been observed to be more precise than a comparable conventional dual sensor, which although considered to be quite accurate can report sensed temperatures that are off by about 0.4 C. This is considered to be a significant discrepancy regarding core body temperature, particularly when it is necessary to identify a tendency towards hypothermia or hyperthermia so that preventive measures can be taken to avoid a critical situation.

[0056] The improvement in accuracy of the inventive enhanced heat-flow sensor is because it considers lateral heat flow also, and is therefore significantly less sensitive to variations in ambient temperature. The improvement in accuracy has been observed for a reference body with a constant temperature at 37.5 C. and a variation in the ambient or outside temperature from 0 C. to 30 C. The body temperature as measured by the inventive enhanced heat-flow sensor remains essentially constant for all values of ambient temperature, whereas a comparable conventional heat-flow sensor exhibits relatively poor performance particularly at the lower temperatures, The enhanced heat-flow sensor according to the invention performs significantly better than its conventional counterpart which does not.

[0057] FIG. 11 shows a further embodiment of the inventive passive heat-flow sensor, realized as a single heat-flow sensor and comprising vertical thermistor pairs S1, S2, giving a configuration of enhanced thermistor arrangements, each comprising a vertical thermistor pair S1, S2 and a lateral thermistor corresponding to the lower thermistor S1 of a neighboring vertical thermistor pair. To determine the core body temperature, the temperature measurement values of the thermistors S1, S2 are examined to identify the pair V.sub.max with the maximum vertical heat flow. Of this vertical thermistor pair V.sub.max, the inner thermistor S1 and outer thermistor S2 will supply the values for T1 and T2 of equation (2) above. A value of T3 can be determined by obtaining the mean temperature of a neighboring vertical pair, for example the vertical pair V.sub.left on the left of the maximum vertical flux pair V.sub.max or the vertical pair V.sub.right on the right, etc. by adding the temperature measurement values of the thermistors S1, S2 and halving the result. The most likely result can be chosen as the value for T3 in equation (2) above.

[0058] FIG. 12 shows a plan view of the single heat-flow sensor of FIG. 11, showing its contact face 11. The positions of the inner thermistors S1 are shown. The location of the thermistor pair V.sub.max with the maximum vertical heat flow is indicated by the dotted line encircling the corresponding inner thermistor. The diagram shows that this thermistor pair V.sub.max has four possible neighbors (two such pairs V.sub.left, V.sub.right were described in FIG. 11), any of which can be used to determine a value of T3 as described above. The advantage of being able to choose between multiple neighboring thermistors is that any erroneous temperature measurement values (arising from sub-optimal contact to the patient's skin, for example) can be identified and disregarded, as explained in FIG. 9 above.

[0059] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. For example, any suitable sensor shape may be used. Equally, different numbers of vertical and lateral thermistors can be incorporated in various embodiments of the inventive enhanced heat-flow sensor. As described above, calculation of core temperature can be performed on the sensor or can be performed remotely. Results can be displayed locally (on a screen) or remotely on a smart watch, mobile phone or the display of any other suitable device. Furthermore, the principle of the invention can be used in an active sensor realization, for example by controlling a heating element to bring the sensor to a zero heat-flux state.

[0060] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a module does not preclude the use of more than one unit or module.

REFERENCE SIGNS

[0061] 1 heat-flow sensor [0062] 2 evaluation unit [0063] 3 microprocessor [0064] 4 display [0065] 5 wireless interface [0066] 8 subject [0067] 10 temperature sensing arrangement [0068] 11 sensor contact face [0069] 12 sensor outer surface [0070] 10A, 10B temperature curve [0071] 40, 41 temperature curve [0072] 90, 91, 92 matrix field [0073] 110, 111 temperature curve [0074] 120, 121 temperature curve [0075] 130, 131, 132 temperature curve [0076] 140, 141 temperature curve [0077] R.sub.B body resistivity [0078] RV, RV1, RH thermal resistivity [0079] S1, SV1 inner thermistor [0080] S2, SV2 upper thermistor [0081] S3 lateral thermistor [0082] T.sub.db core body temperature [0083] T1, T2, T3 temperature measurement value [0084] TV1, TV2 temperature measurement value [0085] V.sub.max thermistor pair [0086] V.sub.left, V.sub.right thermistor pair