WO1999063888A1 - Device for measurements of thermal perception in body cavities - Google Patents

Abstract

In a device for examining the ability of a human being to feel a change in temperature applied to tissue the device has means (1) supplying heat or cold of controlled temperature to said tissue. The means (1) are arranged in a casing (6) which is designed as a probe to be inserted into a body cavity of said human and controlled from the outside.

Description

DEVICE FOR MEASUREMENTS OF THERMAL PERCEPTION IN BODY CAVITIES

The invention concerns a device for examining the ability of a human being to feel a change in temperature applied to tissue. More specifically, the invention concerns the examination of the function of thin myelinated and unmyelinated nerve fibres by measuring the temperature sensibility. Thin myelinated and unmyelinated nerve fibres mainly control autonomous functions but some propagate impulses from cold receptors and heat receptors as well as heat induced pain. There are very few methods to examine the functions of these types of nerve fibres. Yet the unmyelinated nerve fibres comprise 50 % or more of the number of nerve fibres present in the human body.

The autonomic nervous system is mainly concerned with regulation of the internal functions of the body. For example, a number of pathological conditions exist where it is of interest to measure the sensitivity of the vagina not only in connection with incontinence but also with other disorders. Anal incontinence is also a relatively usual problem which receives increasing interest and for which few specific examination methods are available. There are also diagnostic problems in connection with other body cavities. For example, patients with sleep apnea may have a disturbed sensory function which can be diagnosed by the demonstration of an abnormal temperature perception. Many patients undergo treatments which change the function in a body cavity, i.e. after irradiation of cancer and after surgery. At such treatments it is important that those parts having normal functions are saved to the greatest possible extent. In order to diagnose rectal disorders of sensibility balloons have been used for determining the rectal sens- ibility of the increased pressure applied. In US 5 335 669 an inflatable balloon having a temperature sensor is shown, which is used for monitoring the rectal mucosal temperature of the patient during thermal treatment of the prostate. There are a number of systems for measuring cutaneous thresholds for warming and cooling. Probes of different sizes are available for measuring on the face where the inervation is dense or on the hands or the back where the inervation is more sparse. All these what is called thermodes have an rectangular shape and are intended to be placed on the surface of the skin. For example, US 5 191 896 shows an apparatus for measuring threshold sensitivity to a stimulus. The threshold sensitivities for warm sensation, cold sensation, hot pain and cold pain are computerized.

All earlier described devices for examining the ability of a human being to feel a change in temperature applied to the skin have a planar surface which is not consistent with the structures found in body cavities, which are curved. It is also difficult to manufacture a probe comprising such a device sufficiently small and to include biocompatible materials which are efficient.

The object of the invention is to bring about a device for examining the ability of a human being to feel a change in temperature applied to tissue in body cavities whereby the above mentioned drawbacks of the known techniques are avoided.

In order to achieve this purpose the device according to the invention has been given the characterizing features of claim 1.

In order to further explain the invention reference is given to the accompanying drawing in which

FIG 1 is an exploded view shows an assembly to be inserted in a casing designed as a probe according to the invention, and FIG 2 shows the assembled probe which is designed as a finger which can be used for investigating the sensibility in body cavities.

The assembly is according to the invention arranged in a casing which is designed as a probe. It is to be inserted into a body cavity of a human being and controlled from the outside. By introducing into a human body cavity and electronically controlling the temperature from the outside, a persons temperature sensibility can be measured and determined in si tu .

As shown in FIG 1 the assembly 1 comprises contact means 2, temperature changing means 3, and heat exchanging means 4. These three parts are assembled and then mounted in a recess 5 of an outer casing 6 which together with a handle 14 the wires 7, 8, 9, 10, 13 and the tubes 11, 12 constitute the probe, which is shown in FIG 2.

The contact means 2 has as shown in FIG 1 a contact surface facing the tissue of the body cavity to be examined. By applying a curved surface on the contact means 2 an adaptation to the geometry of the organs in the body is obtained.

In order to obtain an adequate stimulus of the tissue when the contact means is in contact with the tissue the thermally active area must give a stimulation which is sufficient to generate a true response. Thus, the contact surface can not have a too small area if a spatial integration of the stimulus is to be obtained, and a contact area of 30 x 15 mm has been found to be adequate. A smaller surface would result in a better resolution but not neces- sary a better response.

The contact means 2 is made of a material which both has suitable heat conduction and adequate heat capacity to serve as a dynamic thermal conductor. Preferably, pure silver is used which is a thoroughly documented material combining excellent thermal properties with excellent biocompatibility .

The contact means 2 contains at least one temperature sensor for measuring the temperature of the contact surface. Preferably, two sensors (not shown) are used whose wires 7 and 8, respectively, transmit signals which at a considerable distance away are compared with each other so that a temperature reading of high accuracy and safety is obtained. By continuously comparing the signals from two sensors a difference indicating a defect in the device will immediately be detected.

The sensor is preferably a thermocouple of a material which generates an electromotive force proportional to the temperature and which can be expressed as μV/°C. The temperature changing means 3 causes a thermal flux in one direction. This can be accomplished by means of an electrically driven Peltier element. The Peltier element - depending on the magnitude and on the direction of the drive current creates a thermal flux between its two plates. Thus, when current is supplied heat can be produced on one side of the temperature changing means 3 and cold on the other. When the polarity of the current is reversed the direction of heat transport is also reversed.

More specifically, the contact means 2 has a thermally active area which is driven by the Peltier element. The Peltier element in turn receives current drive through the two wires 9 and 10. In order to for example heat the thermally active area, the positive current is lead through the wire 9 and the negative current through the wire 10. In order to cool the thermally active area of the contact means the current through the wires 9 and 10 is reversed. In this way the active area of the contact means 2 can obtain a thermal range of +10 to +48 °C, which normally is electronically limited to a more narrow thermal range . The heat exchanger 4 supplies to the temperature changing means 3 energy as heat to be absorbed by the tissue or transports away energy during cold stimulation. A pump (not shown) pumps a fluid via tubes 11 and 12 through the heat exchanger. The heat exchanger is preferably made of aluminium.

In the heat exchanger 4 a third sensor is arranged (not shown) which transmit signals via a wire 13. This sensor is preferably also a thermocouple. As the thermally active area of the contact means is heated or cooled by means of the temperature changing means there is a heat flux through the same. This heat flux results in an accumulation of heat in or removal of heat from the thermal mass of the heat exchanger 4. This is detected by the third temperature sensor which via the wire 13 transmits a signal to pump fluid through the tubes 11 and 12, respectively, in order to restore the initial temperature. If there is an insufficient capacity of thermal transfer and/or a too high thermal load this will be detected as an abnormal temperature, and the whole system will be stopped.

The three parts, i.e. the contact means 2, the temperature changing means 3 , and the heat exchanging means 4 are assembled with a thermally conductive glue, for example an epoxy glue containing silver grains, and then mounted in the recess 5 of the outer casing 6, which constitutes the probe.

The outer casing is designed to have thermally neutral properties. Polyoxymethylene is preferred for the casing since this plastic material withstands normal hospital cleaning procedures, has low thermal conductivity and good biocompatibility.

The outer casing, and thus the probe itself, is also designed to have suitable dimensions for the body cavity to be tested. The probe is suitable for, but not limited to investigation of thermal perceptions in the rectum and vagina .

When the probe is used for rectal measurements the outer casing 6 has a diameter of about 22 mm and is about 195 mm long. The probe has a rounded tip of about 15 mm that ends at the recess 5 which is now occupied by the thermally active area of the contact means 2, which has the same curvature as the outer casing 6.

The probe can of course have other dimensions in de- pendence of the body cavity to be examined. Thus, smaller probes according to the principle of the invention can be constructed for measuring in the mouth and other similar cavities .

When using the probe it is smeared with a gel which can be the same as those used in connection with ECG and ultrasonic measurements . The probe is inserted in the body cavity to which it is adapted.

At a certain moment the temperature of the probe, i.e. the temperature changing means, is allowed to rise. When the patient registrates this heat the temperature of contact means 2 is registered by means of the wires 7 and 8.

Then the temperature is allowed to drop back to the base value which is about 35 °C in rectum. The measurement is then repeated several times with randomized intervals between the application of heat and with constant velocity of application, i.e. the rise in temperature per unit of time is constant, usually 1 °C per second.

The same investigation is then performed in the same way with the application of cold instead of heat, the temperature changing means 3 now serving as a cooler by the current of the wires 9 and 10 being reversed.

Then the probe is turned 90° and the procedures are repeated. In this way the cavity can be investigated all around in segments of 90°. The described method of use, when the temperature is increased or decreased until a test subject detects a temperature change is in the literature defined as the method of limits. Both this method as well as other protocols may be employed when using the invention.

Claims

1. A device for examining the ability of a human being to feel a change in temperature applied to tissue, said device having means (1) supplying heat or cold of controlled temperature to said tissue, c h a r a c t e r i z e d in that said means (1) are arranged in a casing (6) which is designed as a probe to be inserted into a body cavity of said human and controlled from the outside.

2. A device as claimed in claim 1, c h a r a c t e r i z e d in that said means (1) comprise contact means (2), temperature changing means (3), and heat exchanging means (4) .

3. A device as claimed in claim 2, c h a r a c t e r i z e d in that said contact means (2) comprises at least one sensor for measuring the temperature of said device.

4. A device as claimed in claim 3, c h a r a c t e r i z e d in that a first and a second sensor is arranged in said contact means (2), the signals of which are all the time compared.

5. A device as claimed in any of claims 2-4, c h a r a c t e r i z e d in that said contact means (2) has a curved surface which is adapted to the geometry of said body cavity and coincides with the surface of said casing (6) .

6. A device as claimed in any of claims 2-5, c h a r a c t e r i z e d in that said contact means (2) is heat conductive, has heat capacity and is made of a biocom- patible material.

7. A device as claimed in claim 6, c h a r a c t e r i z e d in that said contact means (2) is made of silver.

8. A device as claimed in claim 2, c h a r a c t e r - i z e d in that said temperature changing means (3) comprises a Peltier element.

9. A device as claimed in claim 2 and 3, c h a r a c t e r i z e d in that a third sensor is arranged in said heat exchanging means (3) .

10. A device as claimed in claim 1, c h a r a c t e r i z e d in that said casing (6) is made of polyoxymethylene .