AU740919B2 - Method and apparatus for testing the efficacy of patient support systems - Google Patents

Description

WO 98/30995 PCTUS970813 METHOD AND APPARATUS FOR TESTING THE EFFICACY OF PATIENT SUPPORT SYSTEMS 1 BACKGROUND OF THE INVENTION 2 3 A decubitus ulcer, or pressure ulcer as it is 4 more commonly known, is a localized wound of variable depth caused by prolonged pressure in a 6 patient allowed to lie too still in bed over an 7 extended period of time. Sustained compression of 8 the cutaneous and subcutaneous tissue between the 9 bony prominences of the patient's body and the support structure, e.g the mattress, has been cited 11 as a primary cause of pressure ulcer formation.

12 Thus, the sites most often affected in bed-ridden 13 patients include the sacrum, greater trochanter, 14 heel and scapula these are the sites which usually experience higher pressures or loads due to body 16 weight distribution.

17 18 From the treatment of patients in acute care 19 facilities to their care in the home setting, the incidence of pressure ulcer development, and the 21 degeneration of tissues associated with such ulcers, 22 once formed, present a significant health care 23 problem both in terms of the amount of financial 24 resources expended in treatment and, more WO 98/30995 PCT/US97/00813 1 importantly, in the morbidity and mortality 2 associated with the complications which often arise.

3 Depending on the severity of the pressure ulcer and 4 the medical condition of the patient, it has been estimated that the cost of treatment can be as high 6 as $40,000 (Brandeis et.al., JAMA 264:2905-2908 7 (1990)). In one study it was reported that the rate 8 of occurrence of bacteremia associated with pressure 9 ulcers was 3.5 events per 10,000 hospital discharges. The hospital mortality rate from this 11 complication alone was estimated to be 50% (Allman, 12 Decubitis 2:30-33 (1989)).

13 14 Although current understanding of pressure ulcer etiology is incomplete, it is known that the 16 development of such ulcers is the result of a myriad 17 of factors which often interact with one another in 18 a complex manner. It has been recognized that 19 purely conservative measures can be used to control one or more of these factors and that these measures 21 alone can result in the prevention of pressure ulcer 22 development and in more effective treatment of those 23 which have developed. One conservative measure 24 which has been identified to be of critical importance in this regard, is the choice of 26 effective support surfaces, such as wheelchair 27 cushions as well as other seating devices and, more 28 importantly, mattresses, which are utilized in the 29 day-to-day patient care. In the following WO 98/30995 PCT/US97/00813 1 discussion, the general term "support structure" 2 will encompass such varied products as beds, 3 mattresses, cushions, mattress overlays and covers, 4 and sheets, in addition to operating room tables and other types transitional structures i.e. all types 6 of products with which a patient might have contact.

7 All of the products mentioned above impinge 8 upon defined areas of a patient's body and so 9 present their own unique set of problems and concerns for healthcare workers and researchers in 11 the field of pressure ulcer prevention. For 12 example, the areas at risk of pressure ulcer 13 development as a result of inadequately designed 14 seating devices center primarily around the ischium but can involve the posterior regions of the knee 16 joints and lower thigh. More generalized areas are 17 at risk of pressure ulcer development however, when 18 the design of operating room tables and other 19 transitional structures is examined.

21 22 FACTORS TO BE CONSIDERED IN THE DESIGN OF A SUPPORT 23 STRUCTURE 24 There is no universal support surface which can be effectively used with every patient who might be 26 at risk of developing a pressure ulcer. Indeed, the 27 criteria for developing any type of support 28 structure transcend the purely practical constraints 29 of economy, durability and ease of use. The factors 3 WO 98/30995 PCT/US97/00813 1 which prevent the design of the universal support 2 structure are those associated with the individual 3 patient such as diagnosis; tissue history (previous 4 incidence of tissue breakdown, surgical repair or stress); and body build (percentage of body fat and 6 its distribution or localization). In the design of 7 any type of support structure for the prevention, or 8 treatment, of pressure ulcers, the interaction 9 between these and other patient-related variables together with the three mechanical forces of 11 pressure, shear and friction, all of which have been 12 implicated in the cause or exacerbation of pressure 13 ulcers, is of great importance. A review of the 14 three mechanical forces and their interaction with the support structure, as well as a discussion of 16 the means used to measure them, is informative at 17 this juncture.

18 19 Contact Pressure Contact pressure is that force exerted on the 21 cutaneous and subcutaneous tissues by the patient's 22 body weight and bony prominences on one side and the 23 support structure on the other. The incorporation 24 of material into a support structure which has the ability to reduce, redistribute or modify the 26 pressure forces generated by a patient's body weight 27 and bony prominences is of obvious importance in the 28 design of an effective support structure for the 29 prevention or treatment of pressure ulcers.

WO 98/30995 PCT/US97/00813 1 At present there are a number of devices which 2 are routinely utilized by designers of support 3 structures to measure the ability of their products 4 to reduce contact pressure. These devices range from simple pneumatic types to the more complex, 6 which utilize electro-pneumatic and electro- 7 resistive means. Such devices may employ algorithms 8 to sense pressure change. The pressure change, so 9 detected, is translated by the device and displayed in a standardized form. Some measuring devices use 11 fluids instead of air to sense changes in pressure.

12 13 Pneumatic and electro-pneumatic measuring 14 devices consist essentially of a pressure-reading instrument connected to a probe. The probe consists 16 of an inflatable bladder in the pneumatic devices 17 or, in the electro-pneumatic devices, an inflatable 18 bladder containing a wire grid on each of its two 19 opposing walls (electrical connection is broken when the grids are separated). The uninflated pneumatic- 21 type probes are placed beneath the body site to be 22 measured and air is supplied until, in the electro- 23 pneumatic devices, the two grids are separated or, 24 in the pneumatic devices, until internal pressure is equal to external loading pressure. The contact 26 pressure is calculated as that pressure which 27 corresponds to the pressure between the body site 28 and the underlying support structure as measured by 29 the attached pressure-reading instrument.

WO 98/30995 PCTUS97/00813 1 Electro-resistive devices for measuring contact 2 pressure consist of a probe containing sensors 3 composed of materials whose electrical resistance 4 properties vary with the pressure which is applied to their surface. Such electro-resistive devices 6 for measuring contact pressure can contain single-, 7 or multiple-sensor-probes. Strain gages or strain 8 gage assemblies are usually included as component 9 parts of such pressure measuring instruments. Just as in the pneumatic-type devices, the change in 11 resistance of the sensor(s) is measured by 12 appropriate instrumentation and, by virtue of 13 calibration methods, the contact pressure between 14 the body site and underlying support structure can be estimated from the change in resistance as 16 recorded on the attached instrumentation.

17 18 Shear 19 Shear is defined as a mechanical stress which is applied parallel to a plane of interest. Shear 21 is proportional to the pressure at any given site.

22 Like pressure, it exerts a degree of trauma on 23 cutaneous and subcutaneous tissues, thereby 24 compromising circulation and, as such, it is likely to be an important factor in so-called "pressure 26 ulcer" formation.

27 28 The majority of support structures are 29 contained in an external covering material to WO 98/30995 PCT/US97/00813 1 protect the interior from patient discharges. The 2 external covering material can produce shear stress 3 and one manifestation of such shear stress is the 4 so-called "hammock effect." The hammock effect occurs when the support structure external covering 6 material supports the bulk of the patient's body 7 weight in a manner which is independent of the 8 interior of the support structure. In this 9 situation, the external covering material has a tendency to cause relative movement of the cutaneous 11 and subcutaneous tissues along the sides of the 12 contact area between the external covering material 13 and the patient's body. Shear forces and stress are 14 also generated when the head region of a patient's hospital-type bed is raised relative to the lower 16 portions resulting in slippage of the patient's 17 lower body regions.

18 19 Although clinical literature discusses the significance of shear forces in the development and 21 progression of pressure ulcers in bed-ridden 22 patients, it does not define specific means for 23 measuring the shear forces which cause the observed 24 clinical effects. Indeed, to date, no procedures have been described which will accurately measure 26 the total shear forces experienced by various sites 27 on a patient's body. Nor are there any means 28 presently available which are capable of determining 29 how much of what is presently recorded as a WO 98/30995 PCT/US97/00813 1 "pressure" effect is, in actual fact, a shear 2 effect.

3 4 As stated previously, strain gages are often used as the primary means of detection in devices 6 which are used to measure different types of force.

7 The principle upon which the operation of the strain 8 gage is based is, in essence, a simple one: the load 9 placed on the gage or housing which contains the gage produces a force; the force causes the gage to 11 strain or stretch in response to its application; 12 the force alters the physical properties of the gage 13 such that there is a change in its electrical 14 properties such as resistance; this resistance change can be detected and converted into an 16 accurate measurement of force.

17 18 For the above reasons, strain gages are 19 particularly suited for use in instrumentation for the direct measurement of shear forces. The 21 tendency of tissue to deform due to shear can be 22 detected by the change in such properties as 23 electrical resistance in the attached gage. In this 24 regard, the Y series of encapsulated foil strain gages and G series of foil strain gage manufactured 26 by Omega Engineering, Inc. of Stamford, Connecticut; 27 and the semiconductor strain gages such as types C, 28 D, E, F, G, H, and L supplied by Kulite WO 98/30995 PCT/US97/00813 1 Semiconductor Products, Inc. of Leonia, New Jersey 2 are useful.

3 4 Friction Friction is defined as the force generated 6 between two surfaces as they move across one 7 another. As such, it is a factor which is 8 considered to be of some importance in not only the 9 formation of pressure ulcers, but also in the progressive deterioration of tissues which occurs as 11 a result of their development. When, for example, 12 the external covering of the support structure, 13 described earlier, moves relative to the skin of a 14 patient, frictional forces are generated. When such frictional forces are exerted on the patient's skin, 16 the skin is exposed to frictional drag which causes 17 abrasion of its outermost layers.

18 19 When examining the forces of friction, two factors must be considered the actual force with 21 which the patient's body is pushing against the 22 external covering material and the relative 23 smoothness, softness or lubricity of the external 24 covering material which contacts the skin.

26 The coefficient of friction is the product of 27 such support structure properties as external 28 covering material smoothness, softness and lubricity 29 and the clinical characteristics of the opposing WO 98/30995 PCT/US97/00813 1 external skin. Current methods for measuring 2 friction usually involve dragging a weighted sled, 3 with the material of interest on its contact side, 4 across the surface of the skin.

6 Frictional drag produces a strain on tissue and 7 so an alternative means of measuring its magnitude 8 would be by the use of localized force indicators 9 such as strain gages.

11 CONCLUSION 12 From the foregoing discussion of the importance 13 of contact pressure, shear and friction in "pressure 14 ulcer" development and progression, as well as that regarding the methods available for their 16 measurement, it is apparent that, at the present 17 time, a support structure's ability to reduce the 18 incidence and severity of pressure ulcers cannot be 19 accurately determined prior to it being marketed.

The current pre-marketing test procedures used to 21 determine contact pressure, shear and friction are 22 inadequate or nonexistent there are no universally 23 accepted means of, or procedures for, measuring 24 contact pressure in this context. Reproducibility of results from both within and between testing 26 centers is impractical; the various pressure 27 measuring devices, discussed earlier, produce 28 different readings under the same test conditions.

29 Likewise, the determination of frictional drag, WO 98/30995 PCT/US97/00813 1 mentioned above, is not universally applicable. In 2 addition, there are no methods currently available 3 to measure shear in this context.

4 As a result of the current inadequacies in pre- 6 market testing, patients are exposed to an unknown 7 risk of developing "pressure" ulcers while being 8 treated in healthcare facilities and precious 9 healthcare resources are being potentially wasted on equipment with no measure of efficacy in the area of 11 pressure ulcer prevention or amelioration.

12 13 TOWARDS A UNIVERSAL TESTING SCHEME 14 As discussed previously, the choice of a suitable support structure for the patient at risk 16 of developing so-called "pressure ulcers" is vital 17 in the prevention of this serious and potentially 18 life-threatening condition. As an initial 19 preventative measure, it not only is the most effective means of controlling the problem, but also 21 the most economical. Unfortunately, there are no 22 universally accepted means currently available to 23 test the various types of commercially available 24 support structures before they are introduced into hospitals and other healthcare institutions.

26 Moreover, the majority of testing procedures which 27 are presently utilized, only take into account the 28 contribution of contact pressure in the development WO 98/30995 PCT/US97/00813 1 of pressure ulcers and so, in light of the foregoing 2 discussion, are deficient.

3 4 Most initial evaluations of support structures are performed using individual volunteer subjects of 6 varying physical characteristics of weight, height, 7 anatomical frame, gender and age. The results of 8 such evaluations cannot be duplicated or 9 extrapolated to different physiognomies.

Furthermore, such evaluations are performed merely 11 to provide the documentation required to introduce 12 the support structures into the healthcare facility.

13 14 In reality, at the present time, the true efficacy parameters of the product can only be 16 determined from its actual performance once in-use 17 in the facility. Not only are such means of 18 assessing efficacy undesirable, exposing, as they 19 do, patients to an unknown risk of developing pressure ulcers, but they also provide a potentially 21 meaningless assessment. Even in well-designed, 22 randomized clinical trials, great care must be 23 exercised to ensure strict adherance to the study 24 protocol. Such studies are usually conducted over extended periods of months or even years and involve 26 a large expenditure of financial resources. Failure 27 to comply with the study protocol can result in 28 invalidation of the results and so negate the value WO 98/30995 PCT/US97/00813 1 of the study for use in justifying clinical 2 outcomes.

3 4 Pressure sore development, as discussed previously, occurs as a result of the interaction of 6 a variety of factors. The presence of these various 7 factors, or their interaction, cannot be assessed in 8 the scientifically uncontrolled environment of the 9 healthcare facility.

11 As a result of the inability of current 12 methodologies and procedures to accurately assess 13 the efficacy of support structures used in the 14 prevention and treatment of pressure ulcers, valuable healthcare resources are being drained from 16 an already overburdened system. Resources are being 17 wasted not only in the purchase of products whose 18 efficacy is largely unknown, but also in the 19 treatment of pressure ulcers which develop as a result of exposing patients to products which are 21 not efficacious.

22 23 A preferred methodology for testing support 24 structures to determine their ability to prevent pressure ulcer formation would be one which is both 26 uncomplicated in its utilization and universal in 27 nature one which would give reproducible 28 results no matter where in the world testing was 29 conducted. In addition, given the earlier WO 98/30995 PCTUS97/00813 1 discussion of the present inability to accurately 2 measure the three mechanical forces which have been 3 cited as being of importance in pressure ulcer 4 formation, such testing methodology would also include, at a minimum, some means of accurately 6 measuring contact pressure, shear and friction.

7 8 The present invention contemplates provision of 9 a standardized testing system and method for evaluation of the efficacy of support structure 11 products in the prevention and treatment of pressure 12 ulcers. The manner in which this has been achieved 13 is by the incorporation of sensors of contact 14 pressure, shear and friction into the design of an anthropomorphic model which is representative of the 16 human body in respect to such features as anatomical 17 contours; height, weight and weight distribution; 18 and compliance, flexibility and tissue thickness.

19 As a result of the flexible and adaptable 21 nature of its design, the present invention can also 22 be adapted to include an assessment of other factors 23 which might be considered important in the 24 development of pressure ulcers. The effect of these factors on pressure ulcer development can be 26 assessed alone or in conjunction with other 27 variables such as those of contact pressure, shear 28 and friction already mentioned. Examples of such 29 other factors are temperature and moisture WO 98/30995 PCT/US97/00813 1 accumulation within the skin due to sweating, normal 2 moisture loss from the body and moisture 3 accumulation due to uncontrolled factors such as 4 incontinence. In this regard, the physical properties of the material or materials used to 6 simulate human skin and subcutaneous tissues in the 7 anthropomorphic model combined with the ability to 8 incorporate means of simulating normal moisture loss 9 and sweating within the model e.g fluid reservoirs and heating filaments, would enable clinical 11 investigators or researchers to examine and monitor 12 the role of these factors in the formation and 13 progression of pressure ulcers.

14 In the past, anthropomorphic devices have found 16 extensive use in studies of various aspects of motor 17 vehicle safety and, in a related context, as parts 18 of model systems designed to assess the effects of 19 motor vehicle accidents on the vehicle occupants.

As such, the idea of placing sensors of various 21 types on the surface of, and within, the 22 anthropomorphic device, is not of itself new.

23 However, one novel aspect of the present invention, 24 and one which distinguishes it from the anthropomorphic systems proposed to date, is its 26 placement of particular sensing means at various 27 experimentally-predetermined positions of 28 physiological importance to the development and 29 clinical progression of pressure ulcers. The WO 98/30995 PCT/US97/00813 1 placement of the sensing means is of such sensitive 2 nature that their output as regards contact 3 pressure, shear and friction can be correlated to 4 the actual forces acting on the cutaneous and subcutaneous tissues in vivo. In this way, the 6 anthropomorphic model of the present invention can 7 be used to accurately assess, in a standardized 8 manner, the external factors which will predispose 9 an individual to pressure ulcer formation and their pathological progression.

11 12 This ability to accurately assess the role of 13 external factors in pressure ulcer development and 14 pathological progression imparted by the anthropomorphic model of the present invention is 16 especially valuable when it is remembered that many 17 pressure ulcers are initiated beneath the surface of 18 the skin, usually in the deeper tissue regions. By 19 the time these pressure ulcers are visible on the surface of the skin, they have usually already 21 severely undermined large areas of tissue between 22 the bone and skin surface, often forming channels, 23 sinus tracts and large areas of dead or missing 24 tissue. An understanding of the way in which external factors translate into internal forces 26 beneath the surface of the skin is critical to not 27 only the assessment of the efficacy of new support 28 structures, but also to an understanding of the pathology of pressure ulcer development and progression.

In addition, the positioning of the various sensors within the anthropomorphic model combined with the ability to manufacture the model to a variety of specifications which are representative of the varied forms of the human body allows the contribution of the various forces to be accurately assessed for an infinite variety of body types. The system is thus capable of separating the various forces in a manner which has not been possible up until the present time. Such an ability is an invaluable component of not only a testing system, but also any system designed to investigate the individual and combined effect of such variables as contact pressure, shear, friction, moisture accumulation and temperature in pressure ulcer S 10 development and progression.

The design of the anthropomorphic model system also lends itself to testing and study S programs involving actual human tissue. Sections of human or animal tissue may be introduced into the compartmentalised structure of the anthropomorphic model and tissue viability assessed over time relative to the application of various support structures. The 15 viability of the sections of human tissue will be proportional to the forces acting upon them S and so WO 98/30995 PCT/US97/00813 1 indicative of the efficacy of the support structure 2 being tested.

3 4 SUMMARY OF THE INVENTION The present invention achieves its objectives 6 in a simple, straightforward yet elegant manner.

7 The anthropomorphic model is of stable construction 8 and composed of durable materials so that it will 9 retain over an extended period of time, its characteristics of human-like_ contour; weight and 11 weight distribution; tissue compliance, flexibility 12 and thickness. Its specifications can be so rigidly 13 delineated that it is capable of being manufactured 14 in a reproducible manner in different shapes, sizes and weights which are representative of various 16 classes of male and female body types.

17 18 The sensor means capable of measuring contact 19 pressure and shear are placed at discrete, predetermined locations on the surface of the 21 anthropomorphic model and at experimentally 22 predetermined depths of physiological importance 23 within the portions of the model which correspond to 24 the inner tissues. Sensor means capable of measuring friction are also located on or near the 26 surface of the model at experimentally predetermined 27 positions of physiological importance. Although, 28 the location of the sensor means correspond to those 29 areas of a patient's body where pressure ulcers are WO 98/30995 PCT/US97/00813 1 known to develop, the flexibility of the testing 2 system is such that sensor means may also be easily 3 located at positions which normally experience lower 4 loadings. This permits the actual measurement of forces at an almost infinite variety of sites both 6 before and after the anthropomorphic model has been 7 placed on a support structure. Placement of sensor 8 means at discrete positions on the surface of the 9 anthropomorphic model as well as at predetermined positions of clinical. importance within the model 11 enable the three forces of contact pressure, shear 12 and friction to be measured in as close to the real 13 life situation as is possible.

14 The sensor means are placed sQ that they are 16 easily accessible and so can be removed to check 17 accuracy or replaced when no longer functional by 18 relatively unskilled individuals. The output of 19 each sensor is measured, processed and recorded by suitable instrumentation equipped with programs to 21 collate the data in a form that can be easily 22 interpreted. If desirable, the means for 23 transmitting the data obtained from the sensing 24 means can be located entirely within the model, thereby obviating the need for the attachment of any 26 external means for signal transduction.

27 28 It is therefore an object of the present 29 invention to provide an anthropomorphic model which WO 98/30995 PCT/US97/00813 1 embodies a standardized testing system which 2 produces quantifiable measurements of contact 3 pressure, shear and friction for the evaluation of 4 the efficacy of support structures designed to prevent pressure ulcers or reduce the trauma 6 associated with existing pressure ulcers, so that 7 manufacturers and healthcare facilities alike can 8 determine the efficacy of support structures in a 9 reproducible manner for all types of patient.

11 It is a further object of this invention to 12 provide an anthropomorphic model which will enable 13 clinical investigators and researchers to delineate 14 the role of, and assess the efficacy of support structures in decreasing the effect of other factors 16 e.g. temperature and moisture accumulation, which 17 have been implicated in pressure ulcer development 18 and progression.

19 It is a further object of this invention to 21 provide an anthropomorphic model which simulates the 22 various forms of the human body in such a manner 23 that quantitative measurements of contact pressure, 24 shear and friction can be obtained at predetermined positions corresponding to areas of the human body 26 at risk of pressure ulcer development in order to 27 facilitate research into the relationship of these 28 three mechanical forces to the development of 29 pressure ulcers.

WO 98/30995 PCT/US97/00813 1 If is another object of the present invention 2 to provide an anthropomorphic model from which 3 quantifiable measurements of contact pressure, shear 4 and friction can be obtained under conditions which mimic those which would be experienced by a 6 hospitalized patient such that various clinical 7 parameters of importance to the choice and useful 8 life of support structures can be measured in the 9 controlled environment of the laboratory.

11 BRIEF DESCRIPTION OF THE DRAWINGS 12 FIG. 1 is a front elevational view of the 13 anthropomorphic model of this invention.

14 FIG. 2 is a side elevational view of a typical 16 joint in the limbs.

17 18 FIG. 3 is a side elevational view of the 19 anthropomorphic model of Fig. i.

21 FIG. 4 is an expanded schematic model of the 22 placement of sensors for detecting contact pressure, 23 shear and friction forces in the human skin and 24 subcutaneous layers simulating material.

26 FIG. 5(a) is a schematic representation of an 27 arrangement of sensors for detecting contact 28 pressure, shear and friction forces; the data 29 receiving module, composed of signal processing WO 98/30995 PCT/US97/00813 1 circuits and a signal transmitting terminus 2 assembly; data storage and retrieval\modules; and 3 computer processing assembly.

4 FIG. 5(b) is a schematic representation of one 6 embodiment of 7 the signal detection, transmitting and processing 8 pathway depicted in Fig. 5(a) within a limb of the 9 anthropomorphic model.

11 Fig. 5(c) is a schematic representation of an 12 alternative embodiment of the signal detection, 13 transmitting and processing pathway depicted in Fig.

14 5(a) within a limb of the anthropomorphic model. In this embodiment, the data receiving module is 16 attached by signal transmitting wires to the data 17 storage and retrieval module which is located at a 18 position outside the anthropomorphic model.

19 DESCRIPTION OF THE PREFERRED EMBODIMENT 21 A preferred embodiment of the invention 22 incorporates a number of features. The specific 23 form of those features presented in the preferred 24 embodiment of the invention is in accordance with its use as a model system for testing various 26 support structures for their ability to prevent the 27 formation of pressure ulcers. This application has 28 been selected because of its importance. In other WO 98/30995 PCT/US97/00813 1 applications, other specific forms may be 2 preferable.

3 4 Reference will now be made to the drawings, whereby like parts are designated by like numerals.

6 The anthropomorphic model 10 includes head means 11, 7 neck means 12, and body means 13 which includes 8 chest/rib defining means 14. Limb means 15 include 9 a pair of arms 16, 17, a pair of legs 18, 19, and a pair of hands 20, 21. Joint means 22 provide low 11 friction or frictionless articulated connections at 12 a neck joint 23, shoulder joints 24, elbow joints 13 25, wrist joints 26, hip joints 27, knee joints 28, 14 and ankle joints 29. Incorporation of the joint means 22 into the design and structure of the 16 anthropomorphic model 10 enables the anthropomorphic 17 model 10 to be manipulated into a variety of 18 positions which have a direct relationship to the 19 human form and to changes in loading which result from changes in relative positions of various body 21 parts. The anthropomorphic model 10 can be 22 manufactured in a variety of size and weight classes 23 so that representatives of each class of human body 24 size and shape can be made available for testing.

A given model 10 may also be provided with means 26 (not shown), internal to the model, for attaching 27 discrete concentrated weights, for example in the 28 vicinity of the shoulder blades, buttocks, hips, heels, etc. to simulate various weight classes using single models.

Detachable portions 30 of the anthropomorphic model 10 of this embodiment are composed of layers 100, 200, 300 of a flexible material 31 simulating human skin and subcutaneous tissue. The flexible material 31 simulating human skin and subcutaneous tissue may be uni- or multi-layer depending upon the precise application and testing procedure employed, the flexible material 31 including human skin and subcutaneous tissue may also be blocks of live tissue of human or animal origin.

The layers of flexible skin and subcutaneous tissue simulating material 31 which l- make up the detachable portions 30 of the anthropomorphic model 10 are especially adapted to support or contain various types of sensing means 32, 33, 34. Mounted on the outer S" surface 100 of the skin and subcutaneous tissue simulating material 31 are contact pressure sensing means 32, shear force sensing means 33 and friction sensing means 34. The middle layer 200 of skin and subcutaneous tissue simulating material 31 contains contact pressure I sensing means 32 and shear force sensing means 33. The innermost layer 300 of skin and 15 subcutaneous tissue simulating material 31 contains contact pressure sensingmeans 32 and shear force sensing means 33.

shear force sensing means 33.

WO 98/30995 PCT/US97/00813 1 Sensing means 32, 33, 34 are incorporated into 2 the anthropomorphic model 10 in such a way as to 3 facilitate ease of detachment and replacement even 4 by those unskilled in the art.

6 Each sensing means 32, 33, 34 is of modular 7 design and construction and is coupled to or is 8 integral with a data receiving module 35 composed of 9 a signal processing circuit 36 and a signal transmitting terminus assembly 37, the latter being 11 connected by a plurality of leads 38 or a data bus 12 to data storage and retrieval modules 39 located in 13 predetermined parts of the anthropomorphic model 14 which do not interfere with the ability of the system to take the necessary measurements. The data 16 storage and retrieval modules 39 are each enclosed 17 in a cushioned and rugged protective housing 18 The data storage modules 39 receive and store the 19 output signals from the various sensors and transmit them to a computer terminal 41. The computer 41 is 21 programmed to read the data supplied by each sensing 22 means 32, 33, 34, in a conventional manner.

23 Appropriate algorithms for performing mathematical 24 summing, averaging, statistical analysis or other operations on the data generated by the various 26 sensors to be collated and displayed may be 27 conducted in a manner known to one of ordinary skill 28 in the art.

In an alternative embodiment of the invention, each sensing means 32, 33, 34 is of modular design and construction and consists of a data receiving module 35 composed of a variety of signal processing circuits 36 and a signal transmitting terminus assembly 37 which is connected by a plurality of leads 38 to data storage and retrieval modules 39 located at a position external to the anthropomorphic model As shown in Figure 1, the anthropomorphic model can include an inner support structure, or internal framework, of a similar form to a human skeleton. Ribs 14 of the chest are shown in Figure 1, however, other parts of the human "inner support structure" and even the entire skeletal framework may be incorporated. It is preferred that the anthropomorphic 10 model includes such an internal framework, where the internal framework has prominences at positions corresponding to at least one of: occiput; scapula; sacrum; trochanter; heel; ankle; knee; and ischium. The internal framework of the anthropomorphic model may be composed of simulated bones having a soft core encased in fibreglass reinforced plastic material.

15 The anthropomorphic model may include compartments at positions corresponding to at least one of the heel, ankle, knee, trochanter, sacrufi, scapula, ischium or cranium, where the compartments have the ability to hold blocks of live tissue of human or animal origin.

Commonly available "off-the-shelf' items can be used to sense and record contact pressure, shear and friction. For example, suitable devices for sensing shear forces are the RY21, RY61 and Y series of strain gages manufactured by Omega Engineering, Inc. of Stamford, Connecticut;- suitable devices for measuring contact pressure are those in the 170 series manufactured by Omega Engineering, Inc.; and suitable devices for measuring 26 friction are also strain gages manufactured by Omega Engineering, Inc.

In addition, commonly available components can be utilised to measure other variables, quantification of which might be considered desirable. For example, temperature measuring instruments such as thermistors and thermocouples of suitable dimensions for placement within the anthropomorphic model are available from Cole-Parmer of Niles, Illinois. Also, devices for measuring skin moisture such as the Dermal Phase Meter are manufactured by Nova Technology Corporation of Gloucester, Massachusetts.

Claims (21)

1. An anthropomorphic model system including: an anthropomorphic model simulating the major dynamic characteristics of a human, said anthropomorphic model being adaptably representative of specific classes of human.body form as regards body build and including flexible human skin and subcutaneous tissue simulating 1 0 materials comprising a cutaneous region and a subcutaneous region covering at least parts of the model; sensing means located at predetermined positions on, and in the vicinity of, the surface 15 of the skin defining the cutaneous region and within the subcutaneous region, within the interior of said anthropomorphic model, said sensing means i for measuring physical parameters acting on said anthropomorphic model when arranged in life-like 20 positions resting on a support structure, such physical parameters including pressure, shear and friction forces; and means for detecting and displaying signals from said sensing means whereby decreased or 25 increased signals from said sensing means are indicative of the forces existing at and within the cutaneous and subcutaneous regions.

2. The anthropomorphic model system of Claim 1 wherein said anthropomorphic model includes at least one of: head means; WO 98/30995 PCTUS97/00813 neck means; body means which include chest and rib defining means; limb means which include arm, leg and hand means; a plurality of joint means providing articulated connection means at least at one of neck, shoulder, elbow, wrist, hip, knee and ankle means; detachable- means composed of said flexible human skin simulating materials, said flexible human skin and subcutaneous tissue simulating materials being layered, said detachable means containing force sensing means situated on the 15 surface of said human skin and'subcutaneous tissue simulating materials and at varying depths within; said sensing nmeanH'further including data rece- iinag means and signal transmitting reans; and data storage and retrieval means. o 20 3. The anthropomorphic model of Claim 1 wherein said sensing means includes a strain gage.

4. The anthropomorphic model of Claim 1 S" wherein said flexible human skin simulating materials simulate human skin and subcutaneous tissues as to at least one of the properties of: compliance, elasticity; porosity; surface friction; and thickness. The anthropomorphic model of Claim 2 wherein said flexible human skin simulating materials simulate the human skin and subcutaneous WO 98/30995 PCT/US97/00813 tissues as to at least one of the properties of: compliance, elasticity; porosity; surface friction; and thickness; said .human skin and subcutaneous tissue simulating materials being disposed at least on areas of said anthropomorphic model which correspond to said detachable means containing said sensing means.

6. The anthropomorphic model system of.Claim 2 wherein said detachable means including said *10 sensing means are removable and said sensing means S. are replaceable.

7. The anthropomorphic model system of Claim 2 wherein said detachable means are interchangeable between different types of anthropomorphic models which are representative of different forms of human .bdy.

8. The anthropomorphic model system of Claim 2 wherein said detachable means are specific to anthropomorphic models which are representative of

20. a specific form of human body. 9. The anthropomorphic model system of Claim 1 wherein said sensing means includes a plurality of sensors which are incorporated within at least one of: the outer surface of said huma skin and subcutaneous tissue simulating material, said sensing means capable of measuring at least. one of temperature, moisture accumulation, pressure .shear or friction; WO 98/30995 PCT/US97/00813 the middle layer of said human skin and subcutaneous tissue simulating material, said sensing means capable of measuring at least one of temperature, moisture accumulation, pressure and shear; and .the innermost layer of said human skin and .subcutaneous tissue simulating material, said sensing means capable of measuring at least one of temperature, moisture accumulation, pressure or shear. 10. The anthropomorphic model system of Claim 1 wherein said anthropomorphic model.includes: sensing means capable of signal transduction in response to activation of said sensing means by 15 the generation of force or other physical phenomena; data transmitting means for transmitting said signal to data receiving and storage means, said ransmitting means being contained entirely within .said anthropomorphic model and free of any external transmitting means physically attached thereto except said anthropomorphic model; and data receiving and storage means within Ssaid anthropomorphic model for receiving said signal from said sensing means and storing said signal within memory means. 11. The anthropomorphic model system of Claim 1 wherein said anthropomorphic model includes sensing means for signal transduction in response to activation of said sensing means by the generation of physical parameters including force; WO 98/30995 PCT/US97/00813 data transmitting means for transmitting said signal to data receiving and storage means, said transmitting means being located at a point external to said anthropomorphic model and connected by signal transmitting means to said anthropomorphic model; and data receiving storage means outside said anthropomorphic model for receiving said signal from said sensing means and storing said signal within memory means. 12. The anthropomorphic model system of Claim 1 wherein said anthropomorphic model includes internal means for simulating moisture losses to atmosphere which are normal for a variety of 15 physiological states corresponding to different size and weight classes of the human body. 13. The anthropomorphic model of Claim 1 wherein said model includes an internal framework means, such internal framework means having 20 prominences at positions corresponding to at least one of: occiput; scapula; sacrum; trochanter; o heel; ankle; knee; and ischium. 14. The anthropomorphic model of Claim 1 wherein said anthropomorphic model includes,: an internal framework composed of simulated bones having a soft core encased in fiberglass reinforced plastic material. The anthropomorphic model of Claim 1 wherein said anthropomorphic model includes WO 98/30995 PCT/US97/00813 compartments at positions corresponding to at least one of: heel, ankle, knee, trochanter, sacrum, scapulai ischium or cranium; -said compartments having the ability to hold blocks of live tissue of human or animal origin. 16. The anthropomorphic model system of Claim 1, wherein said sensing means includes a plurality of sensors. 17. The anthropomorphic model system of Claim 10 1, wherein said system is designed for testing the efficacy of a support structure in the prevention S. and treatment of decubitus or pressure ulcers and related conditions; said system including the placement of said anthropomorphic model on a support structure to be tested and wherein the signals from said sensors are indicative of the efficacy or lack thereof of said support structure. 9 *9* 18. The anthropomorphic model as claimed in Claim 1, wherein said flexible human skin and 20 subcutaneous tissue simulating materials include a single layer. 9 19. The anthropomorphic model as claimed in Claim 1, wherein said flexible human skin and subcutaneous tissue simulating materials include at least two layers. A method for measuring the efficacy parameters of support structures to be used in the prevention and treatment of decubitus or pressure ulcer formation including: resting, on a support structure, an anthropomorphic model simulating the major dynamic characteristics of a human and having flexible human skin and subcutaneous tissue simulating materials including a cutaneous region and a subcutaneous region and a subcutaneous region; placing sensing means at specific locations on and within said cutaneous and subcutaneous regions of said model resting on said support structure to be tested for S: efficacy, said sensing means capable of measuring physical parameters including at. least one o* 0 of temperature, moisture accumulation, pressure, shear and friction; and 10 means for collecting and interpreting data obtained from said sensing means to 000000 determine loading at sensing locations to thereby determine likelihood of injury to a human resting on such support structure.

21. The method of Claim 20 wherein said anthropomorphic model component is contacted with said support structure component such that signals are generated bysaid s e S 15 plurality of sensing means located within said anthropomorphic model and said signals are Lo 0 0 collected and interpreted as indicative of the efficacy, or lack thereof, of said support structure.

22. The method of Claim 20 wherein said anthropomorphic model component is interchangeable such that all classes of human size and weight forms, as represented by said anthropomorphic models of differing specifications, can be included WO 98/30995 PCT/US97/00813 in the test procedure.

23. The method of Claim 20 wherein said testing system is standardized by the manufacture of said anthropomorphic models representative of all human size and weight classes, said anthropomorphic models capable of being reproducibly manufactured to predetermined, uniform specifications.

24. The method of Claim 20 wherein said 10 anthropomorphic model contains blocks of live tissue of human or animal origin at various o positions corresponding to at least one of the positions identified at. risk for the development of pressure or decubitus ulcer formation.

25. The method of Claim 20 wherein said anthropomorphic model contains blocks of live tissue is contacted with said support structure and assessment of the viability of said block of live 00"0: tissue is indicative of the efficacy, or. lack 20 thereof, of said support structure.

26. The method of Claim 20 wherein said testing system is used to obtain quantitative measurements of physical parameters, including but not limited to, at least one of temperature, moisture accumulation,, contact pressure, shear and/or friction in research procedures aimed at studying the etiology of, or methods for treatment and/or prevention of decubitus or pressure ulcer formation. WO 98/30995 PCT/US97/00813

27. An anthropomorphic model simulating the major dynamic characteristics- of a human, said anthropomorphic model being adaptably representative of specific classes of human body form as regards body build and including flexible human skin simulating materials. including a cutaneous region and a subcutaneous region covering at least parts of the model;' sensing means lbcated' within the flexible 10 human skin simulating materials of said anthropomorphic model for measuring physical parameters such as pressure, shear and friction forces acting on'said anthropomorphic model; and means for detecting signals from said sensing 15 means for ascertaining at least one of the pressure, shear and friction forces existing within the flexible skin simulating materials.

28. An anthropomorphic model as claimed in claim 27, wherein the sensing means located within 20 the flexible human skin simulating materials is located within the subcutaneous region and wherein said means for detecting signals determine the pressure, shear and friction forces existing within the subcutaneous region.

29. An anthropomorphic model as claimed in claim 27, wherein said sensing means includes sensors located at a number of predetermined positions on, and in the vicinity of, the surface of the flexible human skin and within the subcutaneous region located within the interior of said anthropomorphic model; said sensors for 36 WO 98/30995 PCTIUS97/00813 sensing at least one' of the pressure, shear and friction forces existing at the surface of the skin and within the subcutaneous tissue.. An anthropomorphic model as claimed in Claim 29, wherein said sensors are disposed on, and within the subcutaneous tissue of the model for measuring pressure, shear and friction forces acting on said anthropomorphic model when arranged in life-like positions resting on a support 10 structure; and wherein said means for detecting signals from said sensing means are indicative of the efficacy, or lack thereof, of said support structure.

31. The anthropomorphic model as claimed in Claim 29, wherein said means for detecting signals also includes means for displaying the signals. e

32. The anthropomorphic model as claimed in Claim 31, wherein said sensing means for measuring pressure includes means for measuring contact 9 920pressure between the surface of the skin and any 20 underlying support structure and internal pressure within the flexible human skin simulating materials.

33. The anthropomorphic model as claimed in Claim 27, wherein said cutaneous and subcutaneous regions of said flexible human skin simulating materials comprise a single layer.

34. The anthropomorphic model as claimed in WO 98/30995 PCT/US97/00813 Claim 27, wherein said cutaneous and subcutaneous regions of said flexible" human skin simulating materials comprise at least two layers. A method for measuring the external and internal pressures and forces sensed by parts of an anthropomorphic model simulating the major dynamic characteristics of a human, said anthropomorphic model including flexible human skin simulating materials with a cutaneous region and a subcutaneous region includig: placing sensing means at specific locations on, and within, said flexible human skin of said model; said sensing means capable of measuring physical parameters comprising at least one of temperature, moisture accumulation, pressure, shear and friction; resting said anthropomorphic model on a support structure;.and sensing and interpreting data obtained from said sensing means to determine at least one of temperature, moisture accumulation, pressure, shear and friction at a sensing location on, and within, said flexible human skin. S*

36. A method as claimed in claim 35 wherein the placing of sensing means at specific locations includes the placing of a sensing means within the subcutaneous region of said flexible human skin for sensing at least one of temperature, moisture accumulation, pressure, shear and friction present within the subcutaneous region. 38