Vascular disease is the cause of much morbidity and mortality and may cause poor local tissue oxygenation. Poor local tissue oxygenation may be due to local peripheral or more central vascular occlusion/narrowing of vessel lumen.

It is therefore a first object of the present invention to provide an arrangement for assessing levels of peripheral tissue oxygenation to assist health workers in assessing levels of disease/pathology in a patient, so as to allow them to determine the most appropriate method of treating that patient.

Presently, in Europe alone, approximately one hundred thousand lower limb amputations are performed every year.

To restore the mobility of a lower limb amputee, it has long been known to replace the missing part of a limb with a prosthesis, having a socket shaped to receive a residual limb portion, the residual limb portion typically being cushioned within the socket by an elastomeric sleeve.

However, a number of studies have shown that a poorly fitting prosthesis can cause discomfort to its wearer and, in extreme cases, irreparable tissue damage, as a result of under- or over-pressurisation of a surface portion of a residual limb.

It is therefore a second object of the present invention to provide an arrangement by which the limitations of existing prosthetic devices may be overcome.

A variety of devices are known for intermittently compressing a body part, for example to prevent deep-vein thrombosis (DVT), and it is a third object of the present invention to provide a means for improving the efficacy of such devices.

A variety of reconfigurable articles of furniture and variable pressure cushions and mattresses are also known, for

varying the pressure applied to different parts of a body supported thereon, and it is a fourth object of the present invention to provide a means for improving the efficacy of such devices.

According to a first aspect of the present invention, there is provided an analytical apparatus comprising a plurality of pulse-oximetry sensors arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of a body part and electronic means for monitoring the output of said sensors.

The apparatus may thus be used to detect localised abnormalities in peripheral blood oxygenation levels, indicative of existing tissue damage or the potential therefor.

For example, the apparatus could be used to monitor blood oxygenation around varicose ulcers, around healing wounds, either during or after vascular or amputation surgery, or around the sites of existing or potential pressure sores.

The apparatus could also be used for investigating vascular disease, e. g claudication, best level of amputation, response to surgery. In the assessment of claudication, the apparatus could be used to monitor and record changes in levels of tissue oxygenation after exercise or resulting from a change in ambient conditions, e. g. a drop in temperature.

Furthermore, the apparatus could be used to indicate the need to move a patient to prevent or limit the formation of pressure sores, for example by alerting health workers after a pre-determined level of tissue anoxia has been exceeded over a pre-determined period of time.

Preferably the electronic monitoring means comprise means for processing the measured signals and preferably for displaying the processed signals.

Said processing means may comprise respective processors'for processing the signals measured by each of said pulse-oximetry sensors or a single processor for processing each of the measured signals in turn.

Preferably each of the plurality of pulse-oximetry sensors comprises a reflectance or a transmission mode sensor.

The sensors may be arranged in a sheath, strip, pad or mat, which may be either rigid or flexible, for applying to or wrapping around a body part and may be incorporated into a material such as adhesive strapping, cotton fabric, a hydrogel or silicone.

Preferably each sensor comprises a respective light emitter and receiver.

Alternatively the sensors may be provided by each of a plurality of light receivers arranged to receive signals from a single light emitter or by a single light receiver arranged to receive signals from each of a plurality of light emitters.

Where the apparatus comprises a plurality of light emitters, the emitters may be arranged to emit light at different respective frequencies and/or may be operated in sequence to reduce optical cross talk, the sequence of operation of the emitters being either random or pre-defined.

Additionally or alternatively, where the apparatus comprises a plurality of light receivers, the receivers may be arranged to receive light at different respective frequencies.

Preferably the apparatus comprises a telemetric apparatus, arranged for sensor outputs to be monitored remotely of the sensor array, by the transmission of the sensor outputs to a remote site, either continuously or periodically, via a telecommunications link.

Preferably, a further respective sensor is provided, adjacent each of said pulse-oximetry sensors, for detecting the presence of an adjacent body part. For example, the further sensor may comprise a photo-electric sensor arranged to detect light falling thereon at frequencies other than those used by its respective pulse-oximetry sensor, or a pressure sensor.

In a first preferred embodiment, the sensors are incorporated into the residual-limb-receiving socket of a prosthetic device, most preferably into a cushioning liner of

the socket, e. g. a silicone or hydrogel liner, which liner preferably comprises an elastomeric sleeve or sock for fitting over the residual limb.

In a second preferred embodiment, the measured pulsatile signals are used to provide feedback for controlling the operation of a device arranged to intermittently compress a body part, for example to prevent deep-vein thrombosis (DVT).

In a third preferred embodiment, the measured pulsatile signals are used to provide feedback for controlling the operation of a reconfigurable article of furniture, such as a chair or bed, or of a variable pressure cushion or mattress.

According to a second aspect of the present invention, there is provided a prosthetic device having a socket for receiving a residual limb, the socket having a liner for cushioning the residual limb and incorporating a plurality of pulse-oximetry sensors arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of the residual limb.

According to a third aspect of the present invention, there is provided a liner for the socket of a prosthetic device and incorporating a plurality of pulse-oximetry sensors arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of a residual limb to which the prosthetic device may be fitted.

According to a fourth aspect of the present invention, there is provided a device for intermittently compressing a body part and comprising electronic control means responsive to feedback signals provided by a plurality of pulse-oximetry sensors arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of the body part.

According to a fifth aspect of the present invention, there is provided a reconfigurable article of furniture comprising electronic control means responsive to feedback signals provided by a plurality of pulse-oximetry sensors

arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of a body supported by the article of furniture.

According to a sixth aspect of the present invention, there is provided a variable-pressure cushion or mattress comprising electronic control means responsive to feedback signals provided by a plurality of pulse-oximetry sensors arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of a body supported by the cushion or mattress.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, of which: Figure 1 is a schematic view of a first embodiment of apparatus in accordance with the present invention; and Figure 2 is a schematic view of a second embodiment of apparatus in accordance with the present invention.

Referring to Figure 1 of the drawings, a first embodiment of analytical apparatus is shown comprising a prosthetic device comprising a rigid shell 2 for receiving a residual limb and a substantially transparent, elastomeric liner 4 for cushioning the residual limb within the shell 2, the liner incorporating a plurality of pulse-oximetry sensors 6,8, 10 arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of the residual limb.

The sensors 6,8, 10 are arranged to communicate, via a shared ribbon-cable 12, with electronic control means 14 arranged to process and relay output signals from each of the sensors to remote means 16 for further processing, displaying and/or storing the output signals.

Each sensor 6,8, 10 comprises a respective light emitter, e. g. 18, for emitting light at a plurality of frequencies and an associated light receiver, e. g. 20, for measuring the amount of light reflected by the peripheral

tissue underlying the sensor, at each of said frequencies, the electronic control means 14 being arranged to derive, from the ratio of the amounts of light reflected at each of said frequencies, a measure of the level of localised blood oxygenation.

To avoid optical cross-talk, which might otherwise occur between the sensors 6,8, 10 due to their close proximity to one another, the electronic control means 16 are arranged to synchronise the reading of output signals from the light receivers, e. g. 20, of each of the sensors 6,8, 10, with the sequential illumination of their associated light emitters, e. g. 18.

Thus the apparatus allows a health worker to remotely monitor the condition of a residual limb, to identify any abnormalities in the level of peripheral blood oxygenation at various locations within the socket of a prosthetic device, which may be indicative of an over-or under-pressurisation of the surface of the limb at those locations or to more centralised vascular problems.

It will be appreciated that whilst an apparatus has been described for identifying abnormalities in the level of peripheral blood oxygenation at various locations within the socket of a poorly fitted prosthetic device, the present invention also extends to apparatus, for example in the form of strips, pads or sheaths, for applying to or wrapping around body parts to assist health workers in assessing levels of disease/pathology in a patient, so as to allow them to determine the most appropriate method of treating that patient.

Referring to Figure 2, a second embodiment of apparatus is shown, comprising a variable pressure mattress 22 supported by a reconfigurable support-frame 24 and electronic control means 26 arranged to vary the configuration of support-frame 24 and/or the degree of support provided'by the mattress 22 at different locations across its surface, in accordance with output signals provided by a plurality of pulse-oximetry

sensors 28 arranged to measure pulsatile signals at separate respective locations within the peripheral tissue of a body supported by the mattress 22, to achieve desired levels of peripheral tissue oxygenation at each of said locations.

A further respective sensor 30, e. g. a photoelectric or pressure sensor, associated with each pulse-oximetry sensor 28, provides a means for determining whether a body part overlies the pulse-oximetry sensor 28, and thus whether the output of the pulse-oximetry sensor 28 provides any valid physiological information.

The apparatus thus described provide effective means for detecting localised abnormalities in peripheral blood oxygenation levels, indicative of existing tissue damage or the potential therefor.