GB2172111A

GB2172111A - Swelling monitoring device

Info

Publication number: GB2172111A
Application number: GB08506180A
Authority: GB
Inventors: Malcolm Stewart Binns
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-03-09
Filing date: 1985-03-09
Publication date: 1986-09-10
Also published as: GB8506180D0; GB2172111B

Abstract

A monitoring device for monitoring the swelling of a limb encased in plaster comprises an electrical capacitor in the form of a pair of electrode plates (1,2) spaced apart by a resilient foam (3), whereby when the monitoring device is placed beneath a plaster cast and on the encased limb, the pressure exerted on the device by swelling of the limb will cause variation of the spacing of the electrode plates (1,2) against the resilient bias of the foam (3), and hence variation of the capacitance. Therefore, by monitoring the capacitance, for example by connecting the device to a digital capacitor meter (7), the swelling of the limb as represented by the pressure exerted on the device can be monitored. <IMAGE>

Description

SPECIFICATION Swelling monitoring device This invention relates to monitoring devices for monitoring the swelling of a limb encased in plaster of Paris. At the present time such monitoring relies on clinical estimation.

The object of the present invention is to provide a monitoring device which can reliably provide an accurate measure of the swelling.

According to the invention a monitoring device comprises an electrical capacitor in the form of a pair of electrode plates spaced apart by a resilient means, whereby when the monitoring device is placed beneath a plaster cast and on the encased limb, the pressure exerted on the device by swelling of the limb will cause variation of the spacing of the electrode plates against the resilient bias, and hence variation of the capacitance. Therefore, by monitoring the capacitance, for example by connecting the device to a digital capacitor meter, the swelling of the limb as represented by the pressure exerted on the device can be monitored.

Preferably the electrode plates are of a foil material and the resilient means is a foamed plastics material, such as 4 mm. thick foam sheet.

Since the capacitance of the device is inversely proportional to the square of the spacing between the electrode plates a curve of capacitance C against spacing y of the electrode plates has the equation: C = 1 /y2 The foam material can then be chosen to have a characteristic curve for displacement against applied pressure, such that the device has a substantially linear characteristic for capacitance against pressure.

One monitoring device in accordance with the invention will now be described by way of example with reference to the accompanying schematic drawing.

The device comprises foil electrodes 1 and 2 spaced apart by a layer 3 of foam material.

The electrodes 1 and 2 are fixed to the opposite faces of the foam for example by adhesive. The foil is of the type used to make emergency thermal blankets and the electrodes 1 and 2 are rectangular in shape. The foam is of the closed cell type used commercially in the manufacture of buoyancy aids and is almost perfectly elastic. The foam and foil sandwich is encased in polythene sheet 4, so that its capacitance is not affected by body perspiration. Two wires 5 and 6 are glued by electrically conducting cement to the electrodes 1 and 2 and provide leads for connecting the device to a digital capacitor meter 7.

The device is laid between the patient's limb and the plaster during manipulation of the limb.

Claims

1. A monitoring device for monitoring the swelling of a limb encased in a plaster cast, comprising an electrical capacitor in the form of a pair of electrode plates spaced apart by a resilient means, whereby when the monitoring device is placed beneath a plaster cast and on the encased limb, the pressure exerted on the device by swelling of the limb will cause variation of the spacing of the electrode plates against the resilient bias, and hence variation in the capacitance of the capacitor.

2. A monitoring device according to claim 1, wherein the electrode plates are of a foil material and the resilient means is a foamed plastics material.

3. A monitoring device according to claim 1 or claim 2, wherein the resilient means has a characteristic curve for displacement against applied pressure such that the device has a substantially linear characteristic for capacitance against pressure.

4. A method of monitoring the swelling of a limb encased in a plaster cast, wherein a device according to any preceding claim is laid between the limb and the plaster cast.

5. A method according to claim 4, wherein the device is connected by leads to a digital capacitor meter.

6. A monitoring device substantially as hereinbefore described with reference to the accompanying drawing.