GB2168488A

GB2168488A - A relaxometric sensor

Info

Publication number: GB2168488A
Application number: GB08530100A
Authority: GB
Inventors: Wolfgang Friesdorf
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-07
Filing date: 1985-12-06
Publication date: 1986-06-18
Also published as: GB2168488B; FR2574279A1; GB8530100D0; FR2574279B1; SE463127B; SE8505784L; DE3444628A1; DE3444628C2; SE8505784D0; JPS61141345A

Abstract

A relaxometric sensor for the detection of muscular contraction induced by electrical stimulation in the area of the hand using strain gauges as electrical transducers, is constructed in sandwich form from a resiliently deformable support element 1, a covering element 3 which is also resiliently deformable, and a resiliently deformable insert 2, positioned between the support element 1 and the covering element 3, which carries strain gauges 10, 11 on its upper and under sides, respectively. Depth of anaesthesia is measured by attaching the base 12 to the back of the hand and the tongue 13 to the thumb to detect the amount of thumb movement due to nerve stimulation. <IMAGE>

Description

SPECIFICATION A relaxometric sensor The invention relates to a relaxometric sensor for the detection of muscular contraction induced by electrical stimulation in the area of the hand using strain gauges as electrical transmitters.

In the monitoring of the effects of anaesthesia it is necessary in many cases to ascertain the degree of relaxation of the patient so that, for example, adequate subsidence of relaxation can be established, which is the precondition for extubation. In this connection it is suggested in a paper by W. Friesdorf, M.

Schultz and H.-H. Mehrkens entitled "Eine einfache Methode zur Bestimmung und Registrierung des Relaxierungsgades" (A simple method for determining and recording the degree of relaxation) (DE-Z Anästhesie, Intensivtherapie, Notfallmedizin (German journal of anaesthetics, intensive therapy and emergency medicine), 1984, pp 78-80) that a sensor should be placed on the back of the anaesthetised patient's hand and secured against movement to a finger or preferably the thumb. The sensor incorporates strain gauges which emit an electrical signal when the thumb moves, and this can be displayed or recorded. If a motor nerve is stimulated by electrical pulses, a contraction of the affected muscules is produced.

Conclusions can be drawn as to the degree of relaxation from the occurrence or the strength of the contraction. With complete relaxation no movement of the thumb occurs despite electrical stimulation of the nerves innervating the muscle movement.

Monitoring of relaxation is of great importance, particularly for the termination of anaesthesia, as relaxation must have subsided sufficiently prior to extubation in order to ensure adequate unaided breathing.

According to the present invention there is provided a relaxometric sensor for the detection of muscular contraction induced by electrical stimulation in the area of the hand using strain gauges as electrical transmitters, the sensor being constructed in sandwich form from a resiliently deformable support member, a covering member which is also resiliently deformable, and a resiliently deformable insert, positioned between the support member and the covering member, which carries the strain gauges on its upper and under sides.

A preferred embodiment of the invention provides a relaxometric sensor in which an adequate electrical signal is emitted from the strain gauges in proportion to the amount of movement to be expected. A preferred embodiment also provides an easily handled sensor unit which can satisfy aseptic requirements.

A sandwich construction can be provided in which the individual layers are permanently joined together with sealed edges and are cut to an identical shape. This provides a compact and sturdy sensor which can be easily attached with adhesive tape to the back of the hand. Depending on the desired range of applications (new-born babies, children, adults of various sizes), the relaxometric sensor is produced to the appropriate dimensions as required.

The insert may incorporate the strain gauges, connected up opposite each other to transmit the electrical signal, on a region connected to the moving thumb. The insert may usefully incorporate a cut-out section open on one side towards a cable inlet, using if appropriate a sleeve to prevent kinking.

The support member, insert and covering member each preferably consist of a substantially rectangular base portion and a tongue portion. They may be joined together as integral moulded plastics parts or parts cut to size. The preferred material for the plastics parts is rigid polyvinyl chloride with a thickness of 200 to 600 #m.

As a further development of the invention it may be useful if, in order to adjust the electrical signal values of the sensor, the thickness and elasticity of the individual components (support member, insert, and covering member) are selected in such a way that the strain gauges positioned on the upper and under sides of the insert are displaced from the neutral axis of the sensor according to a predetermined pattern. All three components may, if necessary, be made in laminate form from various materials, e.g. with a thin outer protective layer. In this connection, the support member and covering member can be identical in structure, so that the neutral axis of the sensor is located in the centre of the insert.

An additional improvement may, if apporopriate, be achieved by providing a securing member on the tongue portion for connecting it firmly to the thumb, and a securing member for fixing the base portion to the back of the hand. These securing members can be formed in various ways, but preferably as an adhesive fastening (e.g. tape). In addition, to make it easier to fit, the sensor can be given a curved shape by appropriate bonding of the parts, compression moulding or similar methods.

As a further refinement of the invention, the sensor can be provided with a receiver cell for pulse oximetry. This is a measurement cell comprising two light-emitting electrodes (LEDs) and a photo-detector. The pulse wave and the oxygen saturation of the haemoglobin can be determined non-invasively from the nature and extent of the light absorption.

A preferred embodiment of the invention is shown schematically, by way of example only, in the accompanying drawings in which: Figure 1 is an exploded view of the components of a sensor according to the invention; Figure 2 is a sectional view of the sensor of Fig. 1 when assembled; Figure 3 is a side view of the sensor with securing elements; and Figure 4 shows the application of the relaxometric sensor to the back of a patient's hand.

As can be seen in Figs. 1 and 2, a relaxometric sensor is made up of three components combined in sandwich form, namely a support member 1 next to the skin, an insert 2 and a covering member 3. These components form identically-shaped parts cut to shape and bonded together, and are made from plastics sheet of appropriate rigidity. In the insert 2, a cut-out 4 open on one side towards a cable inlet 5 is provided with a sleeve 6 to prevent kinking. Three connecting wires 7, 8 and 9 which emerge from the cable inlet 5 are joined to terminals of strain gauges 10 and 11 which are located on the upper and under sides of the insert 2.

The support member 1, the covering element 3 and insert 2 each comprise a base portion 12 and a tongue portion 13 attached to it. Fig. 3 illustrates the attachment of a securing member 14 which goes round the thumb, and a securing member 15 with which the sensor can be fixed in the area of the back of the hand. The securing member 14 and the securing member 15 take the form of adhesive-type fastenings, such as shown for example in Fig. 3.

It must be pointed out in connection with the illustrations in Figs. 1 and 2 that the dimensions have been chosen merely to make the basic principle clear. In practice, the substantially rectangular base portion with its rounded corners is about 6 cm long and 5 cm wide. The length of the tongue portion 13 joined to it is about 8 cm for adults.

In Fig. 2 the thickness of the support member 1, the insert 2 and the covering member 3 is shown considerably enlarged; in practice the thickness of the cut pieces of sheeting is only about 500 #m.

Claims

1. A relaxometric sensor for the detection of muscular contraction induced by electrical stimulation in the area of the hand using strain gauges as electrical transmitters, the sensor being constructed in sandwich form from a resiliently deformable support member, a covering member which is also resiliently deformable, and a resiliently deformable insert, positioned between the support member and the covering member, which carries the strain gauges on its upper and under sides.

2. A sensor in accordance with claim 1, wherein the support member, the insert and the covering member are components which have been cut to size and permanently joined together.

3. A sensor in accordance with claim 1 or 2, wherein the insert incorporates a cut-portion open on one side towards a cable inlet.

4. A sensor in accordance with any preceding claim wherein the support memer, the insert and the covering member are formed as a single unit, with a substantially rectangular base portion and also a tongue portion.

5. A sensor in accordance with any preceding claim, wherein in order to adjust the electrical signal values of the sensor, the thickness and elasticity of the support member, the insert, and the covering member are selected in such a way that the strain gauges on the upper and under sides of the insert will be displaced from the neutral axis of the sensor.

6. A sensor in accordance with claim 4, or claim 5 when appended to claim 4, wherein a first securing member is located on the tongue portion and a second securing member is located on the base portion.

7. A sensor in accordance with claim 6, wherein said securing members are adhesive elements.

8. A sensor in accordance with any preceding claim, wherein the sensor is given a curved shape to allow it to fit the back of the hand.

9. A sensor in accordance with any preceding claim, wherein a receiver cell is provided on the sensor for pulse oximetry.

10. A sensor in accordance with any preceding claim, wherein the support member, the insert and the covering member are formed from plastics.

11. A relaxometric sensor substantially as hereinbefore described with reference to Figs.

1 to 4 of the accompanying drawings.