THERAPEUTIC PRESSURE SYSTEM
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority from U.S. Provisional Application Serial No. 61/970,780, filed March 26, 2014.
FIELD OF THE INVENTION
This invention relates to the field of pressure relief systems to apply or relieve pressure and providing comfort to a patient. The invention has particular utility in connection with hospital bed pads or mattresses and will be described in connection with such utility, although other utilities including boots, socks or cuffs for preventing deep vein thrombosis (DVT s) to be worn by a patient during a surgery, after surgery, as well as sitting chair and wheelchair seat pads, and pressure wraps for the body or extremities arc contemplated.
BACKGROUND OF THE INVENTION
Pressure ulcers (also known as pressure sores, decubitus ulcers and bed sores) are areas of localised damage to the skin and underlying tissue, believed to be caused by pressure, shear or friction (Allman 1997). They usually occur over bony prominences such as the base of the spine, hips and heels. Pressure ulcers occur in both hospital and community settings, most often in the elderly and immobile (e.g. orthopaedic patients), those with severe acute illness (e.g. patients in intensive care units) and in people with neurological deficits (e.g. with spinal cord injuries). The development of pressure ulcers is relatively common. A review of epidemiological studies in the UK, Canada and the USA describes reported pressure ulcer prevalence in the UK of between 4.4% in a community unit up to 37% in palliative care
(Kaltenhalter 2001). hi the USA and Canada prevalence ranged from 4.7%) in hospital patients to 33% in spinal cord injured patients in the community. They represent a major burden of sickness and unmeasured effects on quality of life for patients and their careers, and are costly to health care systems. In the UK the cost of preventing and treating pressure ulcers in a 600-bedded large general hospital was estimated at between £600,000 and £3 million per year (Clark 1994). The total cost of pressure ulcers to the NHS has been estimated as £1.4-£2.1 billion annually with most of this cost being due to nurse time (Bennett 2004). The extent to which pressure ulcers are preventable is not clear.
Pressure relief for patients confined to beds for significant periods of time is a significant problem. Pressure sores, such as decubitus ulcers, potentially lead to infections and other conditions or complications. These can occur from prolonged pressure exposure, such as experienced by those confined to beds, whether in a hospital, nursing home, or private residence. Considerable efforts have been made to provide mattress systems or patient support surfaces which effectively redistribute and/or equalize pressure forces at the interactions between the patient and the support surface. Generally speaking, the more sophisticated systems for achieving such pressure reductions are expensive to manufacture and maintain. Today, several vendors manufacture support surfaces which include various elongated air tubes, cells or cylinders combined with foam pieces or perimeters which surround the air tubes. Examples of embodiments having multiple, elongated air tubes are set forth in U.S. Pat. Nos. 5,692,256; 5,412,821 , and 5,070,560. These air tubes or bladders are somewhat large and cannot change the pressure over small areas or locations of the patient's skin within an area where pressure is already applied. Another deficiency of prior art systems is that air or other gasses are highly compressible and thereby not able to apply an accurate amount of force to a specific location within an area in contact with the patient without changing or moving a large surface area in contact with the patient.
Consider, for example, the bed shown in U.S. Pat. No. 5,692,256 which is similar to one available commercially from Hill-Rom, and which requires a special stepped deck which includes an upper deck, and a lower deck coupled to the upper deck by a vertical deck side wall. Recently, the manufacturer has angled the side wall of its bed having stepped decks so that the space between the outermost air cell and the side wall is occupied with a resilient foam bolster. These bolsters, however, limit the amount of area occupied by the air cells.
Hospital beds such as above described are expensive to manufacture and maintain, and have a tendency, due to their design, to be hot, transferring heat to a patient's body, creating an uncomfortable condition for the patient. Also, since current pressure relief systems such as above described require specialized bed frames, they cannot be used with conventional hospital mattresses.
The aim of pressure ulcer prevention strategics is to reduce the magnitude and/or duration of pressure between a patient and their support surface (the "interface pressure"). This may be achieved by regular manual repositioning (e.g. "two hourly turning"), or by using pressure-relieving support surfaces such as cushions, mattress overlays, replacement mattresses or whole bed replacements. The cost of these interventions varies widely; from over £30,000 for some bed replacements to less than £100 for some foam overlays. Pressure-relieving cushions, beds and mattresses either mould around the shape of the patient to distribute the patient's weight over a larger area (constant low pressure devices) (CLP), or mechanically vary the pressure beneath the patient, so reducing the duration of the applied pressure (alternating pressure devices) (AP) (Bliss 1993). CLP devices (either overlays, mattresses or replacement beds) can be grouped according to their construction (foam, foam and air, foam and gel, profiled foam, hammocks, air suspension, water suspension and air- particulatc suspension/ air-fluidised). These devices fit or mould around the body so that the pressure is dispersed over a large area. Alternating pressure devices generate alternating high and low interface pressures between body and support, usually by alternate inflation and deflation of air filled cells. Such devices are available as cushions, mattress overlays, and single-or multi-layer mattress replacements. Turning beds, such as turning frames, net beds, and turning/tilting beds move those patients, either manually or automatically, who are unable to turn themselves. Pressure ulcer prevention is often not the reason for using turning and tilting beds; they may be used in Intensive and Critical Care Units for other reasons, e.g. to promote chest drainage. Why it is important to do this review Health care professionals attempt to reduce the incidence of severe pressure ulcers by the identification of people at high risk and the use of prevention strategies, such as pressure-relieving equipment1.
There are numerous pressure support mattresses intended to prevent the development of bed sores. Examples of these devices are as follows:
1. "Support surfaces for pressure ulcer prevention (Review)" Mcinnes E, Cullum
NA, Bell-Syer SEM, Dumville JC, Jammali-Blasi A, The Cochrane
Collaboration and published in The Cochrane Library 2008, Issue 4 2. BodiTrak Smart Bed by Vista Medical
3. "A Smart Bed Platform for Monitoring & Ulcer Prevention" 201 1 4th
International Conference on Biomedical Engineering and Informatics (BMEI), R. Yousefi. S. Ostadabbas, M. Faezipour, M. Nourani, V. Ngl , L. Tamil, A, Bowling, D. Behan and M. Pompeo
4. Med-Aire 8" Alternating Pressure Mattress Replacement System With Low Air Loss, Drive Medical Device & Manufacturing
5. US005685036A, ALTERNATING PRESSURE MATTRESS SYSTEM AND METHOD
6. US 8,196,239 B2, CLINICAL SUPPORT PAD
7. US 2004/0226102 A 1 , ALTER ATING PRESSURE CUSHION
8. US 2013/0255699 Al , PATIENT- OR TENTING ALTERNATING
PRESSURE DECUBITUS PREVENTION SUPPORT APPARATUS
9. US 2007/0025575 Al , SYSTEM AND METHOD FOR INTEGRATING
TRANSDUCERS INTO BODY SUPPORT STRUCTURES
10. US 8,606,344 B2, INTEGRATED PATIENT BED SYSTEM
1 1. US 2008/0060138 Al, PATIENT SUPPORT SURFACE WITH
PHYSIOLOGICAL SENSORS
12. US 2009/0163819 Al, BODY MONITORING DEVICE, BODY DATA
ACQUIRING METHOD AND METHOD OF DETERMINING THE PRESENCE, LOCATION AND/OR STAGE OF A WOUND
13. PCT/US2009/034557, THERAPEUTIC PRESSURE SYSTEM
The foregoing discussion of the prior art derives, in part, from
PCT/US2009/034557 in which there is disclosed a therapeutic pressure system, comprising: an array of individually addressable electroactive polymer actuators, each actuator comprising a scaled actuator housing containing an electrolyte, one or more polymer actuators that actuate via movement of electrolyte components into, out of, around or within the polymer matrix of the polymer actuators, an actuator support structure for the polymer actuators, working anode and cathode electrodes in working contact with the actuators, circuitry for connecting the electrodes to a power source, and a controller between the power source and the electrodes to control the electrical current to the electrodes.
SUMMARY OF THE INVENTION
The present invention provides an improved therapeutic pressures system comprising an array of individually addressable electroactive polymer actuators, including pressure sensors and feedback controls.
More particular, the present invention provides a therapeutic pressure system comprising a plurality of field individually addressable electroactive polymer actuators formed integrally with or as an overlay to a surface, an array of pressure sensors placed at the surface, and a control for applying a differential voltage between an anode and a cathode of a selected actuator to control a pressure in the actuator.
In one aspect of the invention, the surface comprises an operating room surgical table.
In another aspect of the invention, the surface comprises an operating room table arm rest.
In yet another aspect of the invention, the surface comprises an operating room table leg support.
In still yet another aspect of the invention the surface comprises a bed or mattress or mattress topper.
In a further aspect of the invention, the surface comprises a gurney, or a wheel chair seat or pad.
In another aspect of the invention, the surface comprises an emergency room table.
hi still yet another aspect of the invention, the surface comprises an operating room ramp and head rest.
hi yet another aspect of the invention, the actuators are expandable in a range of +/- 0.25" to +/-0.5" (+/- 0.635 cm to +/- 1.27 cm).
In a further aspect of the invention, the actuators are arranged in a matrix 0.5" to 5.0" (1.2 cm to 12.7 cm) apart.
hi yet another aspect of the invention, the actuators are uniformly spaced along an x and y axis. In still another aspect of the invention, the control system includes a closed- loop control pressure sensor for each actuator in the array.
In still another aspect of the invention there is provided a therapeutic pressure system comprising a body wrap having a plurality of individually addressable electroactive polymer actuators formed integrally with or as an overlay to a surface, an array of pressure sensors placed at the surface, and a control for applying a differential voltage between an anode and a cathode of a selected actuator to control a pressure in the actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will be seen from the following detailed description, taken in conjunction with the accompanying drawings, wherein:
FIG. 1 diagrammatically illustrates a therapeutic pressure system in accordance with the present invention;
FIG. 2 is a schematic diagram of a pressure control system in accordance with the present invention; and
FIG. 3 diagrammatically illustrates compression of a patient's epidermis.
DETAILED DESCRIPTION OF THE INVENTION
A therapeutic pressure system in accordance with the present invention comprises a planar pressure array 10, preferably comprises m by n individually addressable Electroactive Polymer Actuators (EPA) 12 distributed along the X and Y axis, that displace perpendicular to the X - Y plane by an amount ΔΖ(η>ηΐ), as shown in Fig. 1 . Each actuator 12 comprises a polymer core with a cathode 14 at one surface of a containment shell 16 and an anode 18 on the other surface of the containment shell 16. When a differential voltage is applied, the thi ckness of the actuator 12 can be controlled along the Z direction. A pressure sensor 20 is also placed at one surface of the containment shell 16, and is used to control the pressure in the Z direction by varying Z, based on the applied voltage between the anode and cathode.
Electroactive Polymer Activators are known in the art. See, for example,
1. "Behavior in electric fields of smart hydrogels with potential application as bio-inspired actuators" Seon Jeong Kim. Han II Kim, Sang Jun Park 1 . In Young Kim, Sang Hoon Lee, Tae Soo Lee and Sun I Kim, INSTITUTE OF PHYSICS PUBLISHING SMART MATERIALS AND STRUCTURESSmart Mater. Struct. 14 (2005) 51 1-514
2. "Freeform Fabrication of Electroactivc Polymer Actuators and
Electromechanical Devices" Evan Malone, Hod Lipson, Mechanical and
Aerospace Engineering, Cornell University eva .malon.e@.corne:ll.edu.
3. US 2007/0190150 Al, POLYMER ACTUATOR
4. US 2009/0317442 Al, SUPER ELASTIC EPOXY HYDROGEL
5. US 2010/0266896 Al , COMPOSITE MATERIALS INCLUDING AN
INTRINSICALLY CONDUCTING POLYMER, AND METHODS AND
DEVICES
6. US 2012/0029430 Al, HIGH SURFACE AREA POLYMER ACTUATOR WITH GAS MITIGATING COMPONENTS
7. US 2004/0226102 A 1 , ALTERNATING PRESSURE CUSHION
8. US 2013/0255699 Al , PATIENT-ORIENTING ALTERNATING PRESSURE DECUBITUS PREVENTION SUPPORT APPARATUS
9. US 2007/0025575 Al , SYSTEM AND METHOD FOR INTEGRATING TRANSDUCERS INTO BODY SUPPORT STRUCTURES
10. US 8,606,344 B2, INTEGRATED PATIENT BED SYSTEM
11. US 2008/00601 38 Al , PATIENT SUPPORT SURFACE WITH
PHYSIOLOGICAL SENSORS
12. US 2009/0163819 Al , BODY MONITORING DEVICE, BODY DATA ACQUIRING METHOD AND METHOD OF DETERMINING THE PRESENCE, LOCATION AND/OR STAGE OF A WOUND
13. "Behavior in electric fields of smart hydrogels with potential application as bio-inspired actuators" Seon Jeong Kim, Han II Kim, Sang Jun Parkl , In Young
Kim, Sang I loon Lee, Tae Soo Lee and Sun I Kim, INSTITUTE OF PHYSICS PUBLISHING SMART MATERIALS AND STRUCTURESSmart Mater. Struct. 14 (2005) 51 1 -514
14. "Freeform Fabrication of Electroactive Polymer Actuators and
Electromechanical Devices" Evan Malone, Hod Lipson, Mechanical and
Aerospace Engineering, Cornell University cvan. mal one@cornell . edu
15. US 2007/0190150 Al , POLYMER ACTUATOR 16. US 2009/0317442 Al , SUPER ELASTIC EPOXY HYDROGEL
17. US 2010/0266896 Al , COMPOSITE MATERIALS INCLUDING AN INTRINSICALLY CONDUCTING POLYMER, AND METHODS AND
DEVICES
18. US 2012/0029430 Al , HIGH SURFACE AREA POLYMER ACTUATOR
WITH GAS MITIGATING COMPONENTS
19. PCT/US2009/034557, Therapeutic Pressure System
The EPA is housed in an air / fluid impervious flexible and expandable containment shell 16. Changes in Z may be, for example +/- 0.25" to +/- 0.5" (+/- 0.635 cm to +/- 1.27 cm) from their nominal position. Actuator spacing along the X and Y axis may be, for example, 0.5" to 5.0" (1.2 cm to 12.7 cm), uniformly spaced.
Referring also to FIGs. 2 and 3, the therapeutic pressure system of the present invention may be used as a mattress or pad, or pressure wrap, including a ramp and headrest positioning device such as the AirSPACE™ ramp and positioning device available from RMD, Revolutionary Medical Devices, of Tucson, AZ, or an operating table arm or leg support device, an operating or emergency room table, a hospital bed, a gurney, a bed or mattress or other patient rest platform, or a pressure wrap, collectively 24. The actuators 12 in the pressure control array 10 can be driven in an open or closed-loop fashion by a controller 24 such as the Sensor Interface,
Recording, Control and Communications System (SIRCCS). A preferred closed loop EPA control consists of a negative feedback controller as illustrated in Figure 2, where a pressure command is generated and the associated thickness of the actuator is changed resulting in an associated change in ΔΖ. Each actuator 12 is driven to a desired pressure, potentially varying as a function of time.
Referring, in particular to Fig. 3, the epidermis 30 acts nominally as a linear spring where the compression, thus the corresponding pressure seen at the epidural surface 32, is proportional to the transmitted force. A force balance example is shown in Fig. 3, where the weight of the patient, W, is supported by three actuators 12 in a linear array 10. Assuming the interface area between each actuator and the patient's epidermis are equal, one approach is to equalize the pressure seen at any location by making the resulting force transmitted by each interface point equal, hi this case the EPA length, ΔΖ (1 ,n), would be adjusted until the pressure measured, thus the force applied by each actuator, Fi, F2 and F3 would equal W/3 as determined by the commanded pressure, Pzcommand(l,n). Naturally, the corresponding "spring" length in the epidermis would also adjust based on the reaction force. It may also be desirable to have the pressure, thus the resulting force, applied by each actuator alternate, or vary sinusoidal as a function of time. This would be accomplished by varying the actuator length, ΔΖ, in order to massage the cpidcmiis, promoting blood flow.
The present invention has several significant advantages over the prior art. These include:
1. The ability to monitor pressure at each actuator 12 location along the Z axis;
2. The ability to control the applied pressure along the Z axis through closed loop feed-back from a sensor 20 feeding a negative feedback signal to a controller 12 and , driving the actuator 12 length to result in a corresponding desired pressure level;
3. The ability to very actuator length and corresponding pressure along the Z axis in open loop control, without closed loop feedback;
4. The ability to vary the commanded pressure at any point within the array as a function of time;
5. The ability to optimize pressure in terms of minimizing the probability a patient will develop bed sores;
6. The ability to record pressure levels for future reference;
7. The ability to transmit pressure levels, and actuator commands to a central data repository;
8. More Compact- conventional pneumatic and mechanical actuators require significantly more depth, 4" to 10" (10.16 cm to 25.4 cm) versus 0.5" to I" (1.27 cm to 2.54 cm) in accordance with the present invention;
9. Higher actuator density- conventional mechanical and pneumatic systems have 4" to 8" (10.16 cm to 20.32 cm) spacing' s versus spacing' s as low as 1 " (2.54 cm) in accordance with the present invention;
10. Higher bandwidth- conventional mechanical and pneumatic systems have bandwidths that are « 0.1 Hz vs 1 Hz in accordance with the present invention; Higher Reliability- conventional systems have moving parts; an EPA-based active pressure monitor and control array in accordance with the present invention has no moving parts; and
Quiet- pneumatics have motor noise for the pump, and mechanical devices have actuator drive noise, while an EPA-based active pressure monitor and control array in accordance with the present invention is silent.